Molecular Architects, Atomic Blueprints and Medical Progress

The Gibbs Award dinner, June 1946

[An exploration of Linus Pauling’s popular rhetoric on the potential for science following World War II. This is part 2 of 5.]

Modern structural chemistry.” [Acceptance speech for the Willard Gibbs Medal, awarded June 14, 1946 by the Chicago Section of the American Chemical Society] Chemical and Engineering News, July 1946.

In 1946, Linus Pauling was awarded the prestigious Willard Gibbs Medal by the Chicago section of the American Chemical Society for his work in structural chemistry. In thinking about his acceptance speech, Pauling ultimately chose to frame it as an overview of the history of modern structural chemistry.

Pauling began his talk with Lucretius who, in the first century BCE, began thinking about the properties of matter. Lucretius hypothesized that honey was made up of “smooth, round molecules which roll easily over the tongue, whereas wormwood and biting centaury consist of molecules which are hooked and sharp.” From there, Pauling rolled through the work of more contemporary greats including Lomonosov’s explanations of the properties of molecules in solid, liquid, and gaseous states; Dalton’s work on the weight relations of chemical reactions; and Avogadro and Cannizarro’s breakthroughs on chemical bonds.

Next up in the whirlwind tour were Frankland, Couper, and Kekulé’s theory of valence; Kekulé’s subsequent writings on the structure of the benzene molecule; and van’t Hoff and le Bel’s explanation of the right and left-handedness of substances. Rounding out the history lesson were Werner’s work on the spatial arrangement of chemical bonds, and Lewis’ identification of the chemical bond as a pair of electrons shared between two atoms. One outcome of all of these advancements was that the discipline of structural chemistry had moved firmly in the direction of the quantitative as opposed to the qualitative judgments that had permeated Lucretius’ analyses of taste and mouth-feel.

Pauling then noted that some of the most exciting and important developments in the history of modern structural chemistry had occurred during his lifetime. It was, for example, only during the early years of his career that methods for accurately measuring interatomic distances had been developed. Subsequent breakthroughs in methodology had included molecular spectroscopy, x-ray and electron diffraction, and applied quantum mechanics, among others techniques. More recently, new knowledge had been produced about moments of inertia, oscillational frequencies, the elucidation of molecular structures for specific substances including sex hormones and vitamin D, and the discovery of the β-lactam configuration of penicillin. In surveying this work, Pauling was particularly quick to praise the usefulness of x-ray diffraction as a powerful tool.

As he looked ahead, Pauling expressed a belief that the most promising application of modern structural chemistry would be its ability to explain the physiological activity of chemical substances. Previous research in this area had produced few results of importance, but Pauling felt sure that the structures of numerous molecules would soon be elucidated, thus laying the groundwork for new insights into physiological activity and, eventually, medical research on diseases like cancer and cardiovascular illness.  

Molecular Architecture and Medical Progress.” Radio talk broadcast on the New York Philharmonic-Symphony Radio Program and sponsored by the U. S. Rubber Company, October 13, 1946.

The ideas expressed by Pauling in Chicago were taken up again in this radio broadcast, which Pauling used to further explore the relationship between molecular structure and physiological activity. In attempting to make this relationship more understandable to his lay audience, he opened with the example of Penicillin G, a molecule commonly recognized as a powerful antibiotic.

Despite penicillin’s widespread application in medical contexts and its acknowledged significance to human life since its discovery in 1928, the molecule’s physiology, at the time of Pauling’s radio talk, was not well-understood. This circumstance was likewise true of other molecules that had become household names, including DDT, morphine, ether, and adrenaline. While scientists understood their uses and functions, the chemical activity that generates and determines those functions remained out of grasp.

Pauling believed that these connections, and the answers that they might provide, lay in what he called “their molecular architecture.” More specifically, were scientists able to determine the structures of specific molecules, they might then turn their attentions to the structures of the biochemical forms with which the molecule interacts. In the case of the household names molecules – penicillin, morphine and the like – these forms might include enzymes, nerve fibers, and tissues with which the molecules interact to produce a desired effect, such as killing bacteria or numbing pain.

Interatomic distance is one important aspect of molecular structure that Pauling took pains to emphasize to his audience. In order to convey a sense of the scale at which atomic distances are measured, Pauling created a hypothetical world where perspective was shifted in the direction of the commonplace. He began by stating that a single Angstrom – the unit used to measure interatomic distances – is equal to 1/254,000,000th of an inch. In other words, when magnified by a factor of 254 million, one scaled-up Angstrom unit would be equivalent to one inch.

With proportions thus shifted, the average human being in Pauling’s hypothetical world would be about 250,000 miles tall, and a wineglass would be as big as the Earth. Importantly, were this gargantuan wineglass full of liquid chloroform, each individual chloroform molecule would be a mere seven inches across. A molecule of chloroform is made up of one carbon atom, three chlorine atoms, and one hydrogen atom, and on this scale, the carbon atom would be the size of a walnut, each chlorine atom the size of a small orange, and the distance between the walnut and each orange would be 1.76 inches. Scaled back down to its actual size (that is, a wineglass-sized wineglass), that distance would be 1.76 Angstrom units.

Pauling’s point in developing this hypothetical was that, in part because they are both small and complicated, the structures of organic compounds were poorly understood. “This then is the great problem of modern chemistry,” Pauling suggested, “the determination of the molecular architecture of the proteins and other complex constituents of the living organism.”

Indeed, Pauling believed that progress in medicine was particularly dependent upon an improved understanding of molecular structure and physiology. By extension, he saw the future role of the “medical research man” as being equivalent to a “molecular architect.” Armed with an understanding of the molecular structures underlying physiological reactions, this new style of architect would have the ability to create “atomic blueprints” for pharmacological compounds designed specifically to treat particular illnesses.

A Post-War Vision for Science

Linus Pauling, 1946

[Ed Note: Today and in the four posts that will follow, we will be examining a series of popular articles and lectures that Linus Pauling delivered from 1946-1951 that outline his vision for what science might become in world no longer dominated by war.]


Linus Pauling believed that the enormous scientific innovation characterizing World War II had resulted in a landscape where science was more relevant than ever to people’s daily lives. As such, in his post-war (defined here as 1946-1951) popular lectures and articles, he tended to focus on spaces where science intersected with everyday life, be it in medical research, education, or even popular culture.

Pauling’s vision for the future of science was optimistic and premised on the notion that the scientific community would build upon its war-time achievements and thrive in an environment defined by free exchange and ample resources no longer constrained by military imperatives. Major themes that he turned to during this period included the need for the creation of a National Science Foundation and subsequent provisions for large-scale funding of scientific research; the intersection of structural chemistry with biological and biomedical chemistry; and the imperative that scientific research and education be made accessible to the general public.

Pauling also frequently made mention of promising developments in medicine. Citing current breakthroughs in structural chemistry, Pauling predicted a ten to twenty year period of rapid advancement in medical research that would contribute to a sophisticated molecular understanding of disease and facilitate the synthesis of chemotherapeutic compounds tailored to specific illnesses. In pushing forward these ideas, Pauling once again emphasized his concern for the health and well-being of society, and his fundamental belief in the value of improving one’s understanding of the world around them.

Molecular architecture and biological reactions,” Chemical and Engineering News, May 1946

In this 1946 critique, Pauling made the argument that contemporary research on the nature of physiological reactions was falling short of the mark because of a lack of understanding about molecular structure, and a lack of emphasis on the connection between structure and function.

According to Pauling, prior research on physiological reactions had attacked the problem from the wrong direction by surveying the chemical reactivity of molecules. (e.g., the tendency of molecules to break their chemical bonds, the strength of bonds between atoms, and the formation of new chemical bonds.) Pauling instead put forth a different approach that would focus on the size and shape of molecules, and the nature of the interactions between molecules as opposed to within them.

Bolstered by this alternative framing, Pauling believed that researchers would soon arrive upon major new advancements, and that vexing questions would begin to be answered. “The next twenty years,” he predicted, “will be as great years [sic] for biology and medicine as the past twenty have been for physics and chemistry.” At the time that Pauling wrote this, scientists had developed only a rudimentary concept of the structure of proteins, a research topic of keen importance to his own lab. But Pauling believed that without a strong basis in molecular structure, it would be near impossible to gain a complete understanding of protein structures, to say nothing of the physiological processes to which they are fundamental.

Pauling next provided a brief summary of the progress that had been made over the previous forty years on structural questions across the sciences, citing the development of the electron microscope as being particularly crucial.

There was still work to be done though. For Pauling, the molecular world was a “dimensional forest,” and he believed that a particular ecosystem between 10 and 100 Å (or 10-7 and 10-6 cm) was home to tantalizing clues about the nature of growth processes, duplication mechanisms for genes and viruses, and enzyme activity. But the technology of the day had not yet caught up; no method had been developed that could enable scientists to view that unknowable part of the “forest.” As Pauling explained, the era’s electron microscopes could get close, and other instruments could go even smaller, but no tool was quite sophisticated enough to illuminate processes and substances within that size range.

To make this specific issue more comprehensible for a non-scientific audience, Pauling likened the situation to that of a scientist in space, attempting to study the Earth from thousands of miles away. With microscopes, diffraction units, and other scientific technology also appropriately scaled up, such a scientist might be able to “…distinguish Central Park, the rivers, and such aggregates of sky scrapers as Rockefeller Center…,” but would not be able to discern individual skyscrapers.

From there, using chemical methods, they would be able to identify “substances” moving across the surface of the Earth that they could not necessarily see, such as cars, buses, and ships. With an electron microscope, they could uncover information about the size and shape of objects to within ten feet, and through x-ray and electron diffraction, they would be able to study in detail the structure of objects smaller than one foot in diameter. But there was no tool that could handle objects in between these sizes, so the scientist’s understanding of life on Earth would necessarily be tempered by their lack of ability to see anything within that range of focus. Scaled back down to the molecular level, this was the situation in which structural biologists found themselves in 1946.

In order to overcome these difficulties, Pauling advocated for a greater allocation of resources to advance work in structural biology. He also argued that knowing the shapes and sizes of molecules would shed light on their physiological activities, as more and more evidence was suggesting that physical properties – as opposed to chemical properties – determined a great many molecular activities. (This was clearly the case with enzymes: catalysis reactions, it had been shown, only occurred in instances where two pieces of a molecule fit together like pieces of a puzzle.)

With the war now over, buoyed by ample funding, and following his suggestions on the most fruitful lines of inquiry, it was Pauling’s belief that the sky was the limit. “[P]recise information will rapidly accrue,” he suggested, “including ultimately detailed structures of fibrous proteins, respiratory pigments, antibodies, enzymes, reticular proteins of protoplasm, and others.”

The Soviet Resonance Controversy: Outside Views

[Part 7 of 7]

Even though the resonance controversy was largely one contested between Soviet scientists and Linus Pauling, many outside members of the scientific public, as well as the media, weighed in on the dispute. By and large, the reaction was quite supportive of Pauling, with most commentators coming to his defense.

One scientist who definitely fit this bill was George W. Wheland, a colleague of Pauling’s who worked with him to develop resonance theory. In a letter to the editor of Chemical and Engineering News dated August 4, 1952, Wheland denounced the Soviet attack on resonance as being driven by a “patriotic, political, and ideological invective, which from the Western viewpoint, has no scientific content.”

Moyer Hunsberger, a chemist from the University of Chicago and Fordham University, felt similarly, and in 1952 he delivered a series of lectures meant to thwart “the Russian chauvinistic ideological approach” to scientific inquiry. In them, Hunsberger labeled the Soviet position and its steadfast support of A.M. Butlerov an “extremely obvious exaggeration of [his] contributions to organic chemistry.” Likewise, “the intensity and crudeness” of the Soviet condemnation of Pauling’s ideas “appear[ed] to be without parallel in the annals of chemistry.”

Other scientists added their voices in concert. Notably, Harvard University president James Bryant Conant argued that,

If the Russians continue to attempt to force science to follow along a path determined by politics, Russia is sure to grow weaker. If Russians are not allowed to use the resonance theory or are deprived of scientific freedom in any other direction, Russian science will fall behind western science and Russian technology will suffer. I think that Syrkin and Diatkina and other Russian chemists who have been criticized for using the theory are among the most able in Russia today. Their book, The Chemical Bond and the Structure of Molecules is an excellent work. It is based almost entirely on resonance theory – and I think there is no substitution for that.

But scientists weren’t the only ones who came to Pauling’s defense. Many media outlets also published articles about the controversy and, as with the academics, they were strongly in support of Pauling and his resonance theory.

Perhaps the first mention of the controversy in the stateside media appeared in a July 15, 1951 New York Times article titled, “Soviets Dispute a Chemical Theory.” In the article, the author impugns the Soviets for not acknowledging the centrality of resonance theory and even asserts that the Soviet atomic bomb projects were necessarily informed by the work. As such, it was clearly hypocritical for the theory to be described as “bourgeois mysticism” when it had been so important to advancing goals fundamental to the national interest.

Shortly thereafter, on September 1, 1951, the California Institute of Technology News Bureau released a bulletin about the controversy that sought to summarize the Soviet attack and defend the importance of Pauling’s ideas. “The theory is now an accepted part of chemistry,” the News Bureau wrote, “at least in the Western world. It is taught in general and organic chemistry textbooks and has contributed to the simplification of the science.”

These early analyses in hand, other newspapers began to report on the controversy, with some even drawing comparisons between the Soviets’ stance and actions taken by the U.S. government a year prior. In particular, a Seattle Times piece from September 2, 1951 compared the resonance controversy to accusations made by the House Un-American Activities Commission a year earlier, wherein Pauling was branded a communist. By recognizing and naming the similarities between the two controversies, the author of the Seattle Times piece put forth both an exoneration of Pauling’s political activities in the U.S. as well as the perception of his science in the USSR.

That same day, the Washington Star published its own article containing a very similar sentiment, and the steady flow of support continued from there. As the year moved forward, the Los Angeles Times, Newsweek, Time, and the Pasadena Independent were among those publishing popular articles that upheld resonance theory and denounced the Soviet position.

In 1952, the New York Times published a second article investigating the topic. The piece sought to explain resonance theory in basic terms that “every schoolboy” could understand while also responding to lingering objections from Soviet scientists.

According to the article, scientists in the U.S.S.R. had recently reaffirmed their denouncement of resonance theory, calling its ideas “mere illusions, senseless structures.” These critics continued that

Pauling and his like are said to cherish perverted concepts which are typical examples of bourgeois thinking. The man to follow is A.M. Butlerov, who has a more materialistic concept of chemical structures.

This established, the Times article then put forth a clarification. “It may be that resonance structures are illusory,” the author wrote, but “That is not the point. A theory is not a statement of absolute truth. It is an invention, a tool. […] So far, the theory of resonance explains what cannot be explained by older theories of valence.” The piece concludes of resonance theory, “Benighted Western chemists will continue to apply it.”

But not all outside observers were entirely behind Pauling, and one figure in particular deserves mention. In 1977, two years after his passing, a biographical memoir was written of Robert Robinson, the former president of the British Royal Society. In this piece, it was revealed that Robinson did not at all agree with Pauling’s ideas on resonance.

Robinson and Pauling had known one another for over two decades and were clearly friends. When Robinson received the Nobel Prize in chemistry in 1947, Pauling wrote to convey his “heartiest congratulation,” and at nearly the same time Robinson helped Pauling to secure his Eastman fellowship at Oxford University. When Robinson’s wife died in 1954, Pauling reached out to express his “deep affection.” Some years later, Robinson’s daughter gave Pauling a portrait of her father from 1955, which Pauling later put on his desk as a reminder of the times they had shared together “sitting on stools at the little eating house after the Royal Society Meeting” and their “boat trip down the St. John’s River.”

But despite this close personal connection, Robinson differed on the issue of resonance theory. In the biographical memoir, Robinson was quoted as having referred to Pauling’s resonance work as “very misleading” and an “unfortunate contribution” to science. Pauling was upset by this revelation, so much so that he wrote a response in which he argued that Robinson’s beliefs were “based entirely on misunderstanding or incompleteness of knowledge of the nature and early history of the theory of resonance.”

The late Robinson’s critique stood as an outlier though and, upon final reflection, it appeared that Pauling’s experience with the Soviets did not leave a lasting mark. In a Royal Society paper about resonance theory that he wrote in 1977, Pauling addressed the controversy just once, and in it he did not even specifically mention the Soviets. Rather, Pauling’s text indicated that resonance theory had been “rather strongly attacked…because of the failure of critics to understand it.” And with that, he seems to have summarized his feelings about the Soviet resonance controversy in as succinct a manner as possible.

The Soviet Resonance Controversy: Dying Embers

“Glory and Pride of Russian Science,” Pravda, November 22, 1961. Note Pauling’s annotation at far right.

[Part 6 of 7]

After the death of Joseph Stalin in 1953, scientists in the Soviet Union began to decrease the intensity of their attacks on Linus Pauling and his theory of resonance. This process played out for at least another ten years, during which time the combatants’ points of emphasis gradually shifted.

Instead of arguing against the theory because it opposed Soviet ideology, Pauling’s critics now focused on his failure to acknowledge the work of Russian scientists whom they argued were influential to his breakthrough. This difference marked a monumental deviation from the scientists’ earlier platform for opposition. Before, the Soviets put forth a blanket rejection of resonance as an idea, and thus abandoned its use in developing their scientific work. However, post-Stalin, the Soviets tacitly began to recognize the utility of resonance while still arguing for credit that they felt was owed to luminaries of their past.

Pauling also began to soften his rhetoric in defending his theory, perhaps in part because of the complex nature of his relationship with the Soviet Union. The years of the resonance controversy coincided with stateside accusations that Pauling was a communist and a Soviet sympathizer. During this period, Pauling had also been very public in urging the Soviets to slow down the pace of their atomic weapons development and testing. In the midst of these heady issues, the battle to defend resonance was perhaps just not quite so pressing, and it was in this context that the final phase of the resonance theory controversy took place.

Notes used by Pauling in his 1961 Moscow lecture.

The last chapter of the dispute began when Pauling gave a speech on resonance in Moscow, a talk that would have been unimaginable during Stalin’s lifetime. Delivered on December 3, 1961, Pauling made his remarks to the chemistry division of the Soviet Academy of Sciences.

At his hosts’ urging, Pauling began by praising a Russian chemist, Mikhail Vasilyevich Lomonosov (1711-1765), for first theorizing that the properties of chemicals are a result of “their structure as aggregates of atoms.” Pauling’s offering of acclaim was not without calculation however, in that he also argued that that Lomonsov was a free thinker, and that he had used his “imaginative effort” and “high originality” to develop his ideas.

Perhaps most importantly, Pauling stressed that Lomonosov’s ideas were based on conceptual findings, not ideological doctrine. In this, Pauling was clearly trying to emphasize the ways in which Russian science had differed from the more contemporary Soviet approach, with old masters like Lomonosov developing their thinking on the basis of experimental data. By using Lomonosov as an anchor for this argument, Pauling made clear throughout his speech his continuing objection to the Soviet ideological attack on his theory.

Question submitted to Pauling by an audience member following his 1961 Moscow lecture.

The controversy had been brewing for well over a decade by the time Pauling gave his speech, so it would stand to reason that many in attendance still doubted the validity of resonance theory. And indeed, handwritten questions offered to Pauling at the conclusion of his lecture ranged from outright denial of resonance theory to asking whether or not molecular orbital theory or other explanations could be used instead to understand chemical structures and their properties.

Generally speaking though, these audience-generated questions were not ideologically based, perhaps because Pauling had deliberately chosen at the outset to “ignore the criticism [of his theory] on ideological grounds” and instead devoted most of his speech to systematically arguing in support of the science. The case that he made was clear and straightforward, but also imbued with undertones of sadness. Specifically, Pauling mourned the loss of scientific contributions that could have been made had the Soviet establishment bought in to resonance from the beginning. This sentiment comes across most acutely in the talk when Pauling laments that there is not a single “textbook of chemistry published by any Soviet scientist during the past ten years in which the theory of resonance is presented in a reasonably satisfactory way,” an omission that would guarantee that future Soviet students would be “seriously hampered.”

Pauling’s Moscow lecture signaled a clear shift in the arc of the controversy. Though still critical of Soviet science and its lack of fundamental integration of resonance theory, Pauling was at least willing to visit the Soviet Union and concede a small piece of intellectual ground. In the wake of these actions, the controversy moved into its final, least aggressive form.

Publications authored in the months following Pauling’s visit increasingly came to show that the Soviets no longer rejected resonance, but did want to be included in the story of its discovery. One notable example was a May 1962 article by G.M. Bykov titled “The Origin of the Theory of Chemical Structure.” The piece was written in English, a clear indication of its intended audience, and argued that all chemical structure theory should be based on the work of Russian scientists. It is “[t]rue,” Bykov writes, that Russian scientists such as A.M. Butlerov “did not develop and did not always support” other ideas about chemical structures. But for Bykov and his colleagues, Butlerov was “the founder of the theory of chemical structures” and “the establishment of a correct conception of chemical atoms” would necessarily be based on his ideas.

Excerpt from “In the Memory of a Theory.”

Responses of this sort allowed the Soviet academy to protect national pride while simultaneously updating their practices to align with the rest of the world. The shift in rhetoric also helped to end the extreme animosity that had been directed towards Pauling and, by the 1970s, the Soviets had essentially retracted any ideological objection to resonance theory. In fact, in 1972 the popular Soviet science magazine, Znanie Sila (“Knowledge is Power”) published a retrospective titled “In the memory of a theory” that used interviews with M.E. Diatkina to recount the resonance story and its importance in the world of chemical structures.

By the 1970s, Pauling and the Soviets had effectively ended their feud with both sides having offered a bit of a compromise. Even though Pauling never fully acknowledged Russian science as directly influencing his theory, he did concede for the records that Russians had developed some early ideas regarding the structure of chemicals. For their part, the Soviets lessened the intensity and direction of their objections and gradually adopted resonance theory into their modeling.

Despite this thawing of relations, other scientists and the public at large continued to weigh in on the controversy, as they had done since its genesis. The story of these outside perspectives, and Pauling’s responses to them, will be the subject of our final post in this series.

The Soviet Resonance Controversy: Pauling Fights Back

[Part 5 of 7]

Beginning in the late 1940s, Linus Pauling’s theory of resonance came under attack in the Soviet Union, first by scientists and then by the Soviet state itself. The primary points of contention for Pauling’s Soviet critics hinged on the seeming abstractness of his theory as well as his failure to acknowledge Russian and Soviet scientists deemed important to the development of his ideas. The more they considered the theory, the more their contempt grew, to the point where Soviet chemists were eventually called upon to lead an “army of many thousands strong” against Pauling. These sentiments did not reach Pauling until 1951, a full two years after the debate within the Soviet Union began. Though surprised by the tone of the Soviets complaints, Pauling did not stand down and instead launched a counter-offensive of his own in support of his scientific work.

Pauling became aware of the brewing controversy in August 1951, when a translated article from the Soviet scientific literature was sent to his office. In response, Pauling wrote a charged letter to the Soviet Academy of Sciences condemning the piece and upholding the importance of resonance theory as key to growth in the field of structural chemistry. In the letter, Pauling made clear his belief that the critics’ rhetoric was falsely placed and, indeed, that “the attempted suppression of a part of science is based upon a faulty conception of the nature of science.”

Pauling took particular objection to the ideological arguments against his theory, finding them baseless since they did not intersect at all with the scientific principles that informed his theory. He also warned of the dangers of refusing to incorporate resonance into an entire nation’s scientific vernacular, judging that “Any chemist in the modern world who attempts to carry on his work without making use of the theory of resonance […] is seriously handicapped.”

At the conclusion of the letter, Pauling took pains to praise the two Soviet scientists, Ia. K. Syrkin and M.E. Diatkina, who had translated his work, had spread word of his theory among their colleagues, and who had ultimately been forced to recant their support. In Pauling’s view, the duo were “among the most able chemists in the USSR.”

Pauling’s reply was met with scorn in the Soviet Union, and as a direct result of the letter, the Soviet Academy organized a special meeting to specifically discuss and condemn resonance theory. Held at the end of 1951, the meeting was attended by over 400 people and featured public denunciations of Pauling’s work by no fewer than forty-four prominent Soviet scientists.

One especially notable speaker was Ia. K. Syrkin, the erstwhile translator of Pauling’s Nature of the Chemical Bond. In his presentation, Syrkin introduced his remarks by suggesting that Pauling’s

substitution of the real molecule by a set of resonance structures for the sake of convenience led to an arbitrary and speculative element, and brought about what looks like an explanation, instead of an actual critical analysis and discussion of the mechanism of chemical reactions.

While it is unclear if this notion represented Syrkin’s true feelings, it is reasonable to presume that his words echoed the sentiments of many in attendance. As he moved forward through his talk, Syrkin put forth a standard criticism of resonance objecting to the notion that a molecule might not have a discrete structure. This argument, of course, was grounded fully in Soviet ideology, and specifically the belief that everything must be real and known.

Joseph Stalin lying in state

As it turned out, Pauling’s letter and the Soviet Academy meeting that followed marked the crescendo of the resonance theory controversy. Following the conclusion of the 1951 conference the debate continued to simmer, with small attacks volleyed by both sides for another two years. But in 1953, curiously, the controversy came to an end, specifically because of the death of Soviet Premier Joseph Stalin.

The end if Stalin’s reign ushered in a new era for the Soviets, one where it was no longer imperative to uphold orthodoxy for fear of severe punishment, including death. And the fact that the Soviet scientific community did not pursue its condemnation of resonance theory with any vigor following Stalin’s demise suggests that the debate was never actually rooted in beliefs about problems with the science of resonance. More likely, resonance was just one of many convenient targets for Stalin and other Soviet figureheads in their war against ideas that were ideologically incongruent with Soviet doctrine.

Whatever the case, after 1953 the resonance controversy was effectively concluded, though a few actions remained to be taken by both parties involved. These activities, as well as the western scientific world’s take on the dispute, will be the focus of our final two posts in this series.

The Soviet Resonance Controversy: Escalating the Attack on “Bourgeois Science”

O.A. Reutov

[Part 4 of 7]

In late 1940s and early 1950s, the culture of Soviet science was dominated by Lysenkoist thinking, with little room permitted for other points of view. Indeed, any work that did not fall strictly in line with Lysenkoist ideology was condemned, and those scientists who were brave enough to uphold contrary beliefs were routinely imprisoned or even killed. This period, which coincided with the end of Joseph Stalin’s reign as premier, was clearly not an environment that encouraged innovation; rather, conformity ruled the day.

By extension, the most lauded Soviet scientists of the era were those who remained ideologically attuned to accepted beliefs, and it was in this environment that pitched opposition to Linus Pauling’s resonance theory emerged. The controversy then, was not so much one based on scientific opposition, but was instead steeped in perceived ideological differences.

As noted in our previous post, Ia. K. Syrkin and M.E. Diatkina’s books – including their translation of The Nature of the Chemical Bond – did much to increase awareness of resonance theory within the Soviet scientific community, and in due course the theory was attacked. In 1949 V.M. Tatevskii and M.I. Shakhparanov became the first authors to criticize the theory in the Soviet literature, and seven more articles followed from there. Much of this work received the formal backing of the Soviet state, and all were approved for publication by the Scientific Council of the Institute of Organic Chemistry of the Academy of Sciences.

Reviewing these articles today, it would appear that more than four hundred Soviet scientists were working in some way to disprove resonance theory within the Soviet Union. The sentiment that emerged from this work held that Pauling’s resonance theory was scientifically unsound because 1) it was not ideologically congruent with Soviet ideology, and 2) it did not recognize the work of previous Soviet or Russian scientists.

The framework established by the seven articles set the stage for the next chapter in the controversy: the approval of an official stance on resonance by the Soviet government.

As part of the tradition of Lysenkoist thinking, Soviet scientists periodically held conferences where theoretical doctrine was debated and a specific piece of ideology was declared the “winner.” These winning ideas would, in turn, become the Soviet government’s supported theory, at which point no other competing theory would be allowed.

In 1951 it was resonance theory’s turn to be debated and, to the surprise of few, it was ultimately decided that Pauling’s ideas were not to be considered as part of the Soviet doctrine surrounding the structure of molecules. Furthermore, according to a U.S. State Department document, a decree was issued that “all remnants of the mistaken conceptions of resonance” were to be eradicated.  

The official Soviet position on resonance theory was disseminated in an article by O.A. Reutov in the Journal of General Chemistry of the USSR and titled, “Some Problems of the Theory of Organic Chemistry.” In it, Reutov systematically attacked Pauling’s ideas as “bourgeois science” and “alien reactionary ideas” that did not take into account Soviet foundational work on molecules.

A.M. Butlerov

According to Reutov, Russian scientist Aleksandr Mikhailovich Butlerov had developed the “true” chemical structure of the molecule, and he argued that Pauling evinced an “insufficient appreciation as well as an incomplete understanding and a perversion of the Butlerov theory of structure.” Pauling’s omissions were so egregious as to force Reutov to conclude that the theory of resonance had been formulated, at least in part, for “the belittlement of the importance of Russian science.”

Reutov’s rhetoric only escalated from there. “[I]t is urgently necessary,” he wrote, to criticize resonance on the “basis of Marxist-Leninist methodology,” a passage that all but admits that the controversy had little to do with scientific thinking. And this needed criticism would reliably be carried out by Soviet organic chemists who, to use Reutov’s words, “form an army of many thousands strong.” By the end of the article, it was clear: the Soviet scientific community was ready to attack western ideas on the chemical bond, and Pauling was their primary target.

Because Reutov’s article was originally published in Russian and chiefly circulated within the Eastern Bloc, Pauling did not find out about it for several months. In August 1951 he finally received a copy from the Consultants Bureau, a translation center specializing in scientific journal articles and based in New York. Pauling was understandably unhappy with the content and tone of the article, and expressed hope that “some action can be taken to stop this attack,” which to him was a “very vigorous one.”

The Soviet Resonance Controversy: Beginnings

Trofim Lysenko

[Part 3 of 7]

Linus Pauling’s resonance theory, while initially a bit difficult to grasp, gradually became an essential tool for predicting and understanding chemical structures. Widely lauded for the links that it provided between classical chemistry and the new quantum mechanics, the theory was also valued for its practical applications in molecular modeling.

But not all found comfort and solace in resonance. In particular, many Soviets viewed Pauling’s theory as an affront to their ideology, regardless of its chemical “correctness.” For these critics, an abstract hybrid model of the molecule – one lacking a foundation in a quantifiable reality – was too troublesome to ignore.

Pauling developed his theory of resonance in a series of papers authored in the early 1930s, and eventually codified the work in his 1939 book, The Nature of the Chemical Bond. Soviet scientists were surely aware of resonance theory throughout this time period, but it appears that ideological interest in Pauling’s ideas did not fully manifest until after World War II. This was likely because, during the war, the Soviet government diverted scientific work away from theoretical investigations in favor of practical applications that would benefit the war effort. Shortly after Word War II ended however, Soviet scientists Ia. K. Syrkin and M.E. Diatkina translated The Nature of the Chemical Bond into Russian. The tandem then wrote their own book outlining ideas on structural chemistry; a book that was based on resonance theory.

Though they had grounded their text in well-established chemical theory, Syrkin and Diatkina’s work was almost immediately criticized within the Soviet Union. In 1949, Soviet scientists V.M. Tatevskii and M.I. Shakhparanov published an article in the journal Voprosyi Filosofii (Questions in Philosophy) titled, “About a Machistic Theory in Chemistry and its Propagandists.” In it, the authors contended that Syrkin and Diatkina were obliged to carefully critique Pauling’s resonance theory, rather than bestow upon it “laudatory” praise. The paper then points out that Syrkin and Diatkina did not include

even one mention of the works of Russian or Soviet scientists…it was expected that the translator and editor, fighting for the honor of the Soviet science, would have seen to it to fill in this gap.

“Still worse,” the authors continued, “the annotations which Syrkin gives at the end of the book are represented primarily as indication of the works of American and English chemists.” This given, one could only conclude that Syrkin and Diatkina were merely “propagandists for the known-to-be erroneous and vicious theory of the American chemist, Pauling.”

Tatevskii and Shakhparanov’s views were not anomalous. In fact, the Soviet Academy of Sciences itself viewed Syrkin and Diatkina as being in “serious error” for “championing the theory of resonance or failing to expose its supposed fallacy.” The rhetoric only escalated from there, and in 1951 Syrkin and Diatkina were forced to recant their belief in resonance theory. In his recantation, Syrkin was famously quoted as saying that he had “overestimated second rate works of foreign scientists.”

On the surface, the criticism of Syrkin and Diatkina seems to have emerged primarily from their support of a non-Soviet scientist. And while this was certainly a factor, the attack was also a product of a larger ideological push within Soviet science that traced its origins to the 1930s and a man named Trofim Lysenko.

An agronomist, Lysenko came to symbolize the ideal Soviet man; a notion that received the full support of Premier Joseph Stalin. Lysenko had been born into relative poverty but eventually gained entry into the Kiev Agricultural Institute, where he studied wheat production. It was there that he began to develop the ideas for which he would become well known.

Lysenko believed that if he could freeze winter wheat, he would be able to force early germination of the crop, a process known as vernalization. He also believed that this early germination would in turn become a heritable characteristic. A breakthrough of this sort was highly desirable in the Soviet Union, in part because the vast nation had experienced multiple food shortages due to unseasonably cold winters and poorly structured collectivist agricultural practices. In Lysenko, Stalin saw the promise of more easily feeding the Soviet population, and the scientist quickly grew in stature as a “man of the people.”

But Lysenko’s ideas were attractive on ideological grounds as well, chiefly because his ideas on vernalization took a Lamarckian approach to evolution. Simply put, Lysenko believed that evolution was something that could be controlled by man; that the people had the means and ability to enact and propel genetic change.

This idea ran counter to those prevailing in other parts of the world and specifically the United States, where a more Darwinian notion of evolution had been adopted. In the Darwinian model, evolutionary change occurs by random chance and individuals do not possess the ability to create lasting heritable impact through their own actions. For the Soviets, the Darwinian model was seen as bourgeois, a word that was widely held in contempt. In contrast, Lysenko’s view of evolution was one that put the state in control, and it was absolute.

Given this context, it becomes easier to see how resonance could be viewed as being counter to Soviet ideology. And within the USSR, an alternative theory was accordingly developed by a Soviet chemist named Gennadi Chelintsev, who aspired to become the chemistry and biology equivalent of Lysenko.

Chelintsev applied Soviet ideology to chemistry in his book, Essays on the Theory of Organic Chemistry. Importantly, Chelintsev used the book to argue that every molecular compound had only one discrete structure. His ideas were appealing to many Soviet scientists because, as with Lysenko, they were primarily based in the mechanistic world view that was so deeply enmeshed in Soviet ideologies.  

By translating The Nature of the Chemical Bond, Syrkin and Diatkina had brought Pauling’s ideas on resonance to the widespread attention of Soviet chemists, a process that allowed many to become aware of a scientific concept that was contrary Soviet ideology. In reaction, Chelintsev and others found in Pauling’s theory a perfect tool for villainizing non-Soviet science. And while Chelintsev’s book did not target Pauling outright, it did bring attention to a conflict that would continue to grow in the years to come.

Pauling Supports His Resonance Theory

Portrait of Linus Pauling, 1930s

[Exploring the theory of resonance and the Soviet resonance controversy. Part 2 of 7.]

Linus Pauling was able to develop his resonance theory because of his belief that quantum mechanical principles could be applied to molecular architecture. And even though the theory did not always predict chemical structures and bond strengths with supreme accuracy, Pauling worked hard to defend his ideas. This firm belief in resonance permeated many aspects of Pauling’s work for years to come, and the imperative to defend it arose in more than one instance as well.

Resonance theory informed the two schools of thought then-prevailing for chemists interested in quantum mechanics and the chemical bond. These two modes of thinking were the Valence Bond (VB) theory and the Molecular Orbital (MO) theory. And while both theories used the concept of resonance to explain molecular structure, neither was able to predict all structures all of the time.

One might assume that this variability would have troubled Pauling, but if so, it did not cause him to falter in his conviction that resonance was the best tool available for accurately describing states of matter on the molecular level. Perhaps because of this, Pauling ultimately preferred the VB theory, for which hybridization of orbitals is the mechanism by which molecular shape is explained. That said, Pauling was also aware of the utility of MO theory and, in at least one instance – a study of cyameluric acid – he was forced to use MO theory to explain the structure, having concluded that his application of VB theory was inaccurate.

But incidents like this did not weigh heavily on Pauling, who remained very confident in the soundness of his ideas. Notably, in his 1939 book, The Nature of the Chemical Bond, Pauling explained away the incongruities between VB and MO theory and upheld resonance by stressing that, “the convenience and value of the concept of resonance in discussing the problems of chemistry are so great as to make the disadvantage of the element of arbitrariness of little significance.”

While he took pains to press the usefulness of resonance theory, Pauling sometimes found it more difficult to explain it vagaries. On a conceptual level, one of the theory’s biggest hindrances to acceptance was its statement that the “correct” structure of a molecule is a hybrid of all possible isomers of the molecule. This effectively meant that, in a resonating structure, all possible isomers exist simultaneously, an idea that proved confounding for many. Prior to resonance, the conventional wisdom was based on August Kekulé’s description of rapidly changing isomers. Pauling was sure that, in order for resonance theory to work, the idea of isomers shifting from one to another had to be abandoned.

In making the case for resonating structures, Pauling wrote that

a substance showing resonance between two or more valence-bond structures does not contain molecules with the configurations and properties usually associated with these structures.

Of the various Kekulé structures, Pauling suggested that, “taken together, [they] provide a rough description of the wave function of the molecule in its normal state.” The implication, of course, was that resonance theory offered a more precise set of tools for understanding molecular architecture, once one was ready to clear a few conceptual hurdles.

Christopher K. Ingold

In time the initial sense of confusion was overcome, and the utility and brilliance of Pauling’s resonance theory made it widely accepted. While some saw resonance as heralding a promising new direction for the application of chemistry, others found the theory appealing simply because it seemed to solve so many problems. Early praise came in 1933, when the esteemed British chemist Christopher K. Ingold declared the theory as having effectively resolved lingering questions about the stability of aromatic compounds.

Ingold’s colleague Nevil V. Sidgwick also became a big supporter of resonance theory. Sidgwick was a well-respected scientist, and his endorsement of resonance helped to cement its status as a leading model for understanding chemical structures. A few years later, in his 1944 book, The Theory of Resonance and its Applications to Organic Chemistry, University of Chicago professor George Wheland confirmed resonance as being

the most important addition to chemical structural theory that has been made since the concept of the shared-electron bond was introduced by G.N. Lewis.

Pauling too believed in the utility of resonance throughout his life. He argued in particular that the theory was especially well-suited to “aromatic molecules, molecules containing conjugated systems of double bonds, hydrocarbon free radicals, and other molecules to which no satisfactory single structure in terms of single bonds, double bonds, and triple bonds can be assigned.” He also believed that “resonance provides an explanation of the properties of many inorganic molecules. For example, the carbon monoxide molecule.” Pauling likewise suggested that resonance theory “permitted the discovery” of the alpha helix and associated models comprising “the most important secondary structures of polypeptide chains in proteins.”

In time, resonance theory would become universally used and applied, but not before Pauling was forced to wrestle with an unusual conflict coming out of the Soviet Union. This controversy, which lasted for nearly five years, will be introduced in our next post.

What is Resonance Theory?

Linus Pauling, 1931.

[Ed Note: In 2009, we dipped our toes into an unusual Pauling controversy involving the theory of resonance and Soviet scientific dogma. Today we begin a much more detailed look at the “Soviet Resonance Controversy,” beginning with a discussion of the scientific work that resided at the heart of the matter. This is Part 1 of 7.]

Linus Pauling’s resonance theory helped to unify the classical roots of organic chemistry with the new field of quantum physics. In so doing, the theory provided a hugely important framework for understanding observed atomic behaviors that did not correlate with then-known mathematical explanations or models of the atom.

The theory would also help to usher in an onslaught of new approaches to organic chemistry and the nature of the chemical bond, lifting, in Pauling’s words, “the veil of mystery which had shrouded the bond during the decades since its existence was first assumed.” It was, in short, one of the most adaptive and applicable postulates ever put forth by Pauling.

But the theory of resonance was not immune to controversy. Specifically, it was initially not widely accepted within the scientific community in the United States and, in a very different way, abroad in the Soviet Union. The disputes surrounding the theory were ultimately short-lived though, and Pauling’s ideas on resonance continue to inform today’s understanding of molecular architecture.

August Kekulé

Pauling’s ideas on resonance were grounded in the work of several other scientists but most notably August Kekulé and Werner Heisenberg, both of whom were also interested in the structure of molecules.

Kekulé (1829-1896), a German chemist, notably devised a proposed structure for benzene, an aromatic hydrocarbon of interest to many. Kekulé’s model put forth a structure consisting of six carbon atoms forming a ring, with hydrogen atoms attached externally to each carbon. Though intriguing, this basic structure did not explain where, on the interior carbon ring, double bonds were located. Partly because of this, Pauling would later lament that, “the Kekulé structure for benzene is unsatisfactory.”

Shortly after Kekulé published his basic benzene structure, multiple isomers – or alternative structures – of the same compound were predicted and even isolated by Kekulé. But even these breakthroughs were not enough to explain the “correct” model of benzene. Recognizing as much, in 1872 Kekulé posited that, in actuality, benzene “oscillates” between the various isomers, and that all isomers may in fact be regarded as “correct.”

This notion of oscillation between isomers was hugely important, but despite its utility Kekulé never succeeded in accurately predicting the “true” structure of benzene. The solution to the benzene puzzle would lie in waiting for nearly sixty more years and would rely heavily upon Pauling’s resonance breakthrough.

Despite its shortcomings in accurately predicting a structure for benzene, Kekulé’s oscillation theory served well in disrupting traditionally held beliefs regarding the number of valence electrons that must be present in aromatic compounds. This, in turn, helped to usher in new theories about the chemical structure of aromatic compounds more generally.

By the 1920s, a community of American, British and German chemists had developed a set of theories related to aromatic compounds that built on Kekulé’s ideas. The group’s basic hypothesis was that, instead of molecules oscillating between various isomers, perhaps all isomers actually existed simultaneously. This idea of simultaneous existence piqued Pauling’s interest because it seemed related to work that he was doing with quantum mechanics — specifically, ideas related to quantum resonance that had been introduced by Werner Heisenberg in 1926.

Werner Heisenberg

Heisenberg (1901-1976), a contemporary of Pauling’s, was working to understand the wave mechanics of subatomic particles. As part of this work, he theorized that, on the subatomic level, molecules exist in quantum states – meaning discrete states – and that the actual wave function of a given molecule can be described as the sum of its various quantum states. Heisenberg coined the term resonance to refer to this process — e.g., the summation of various quantum states to comprise a molecule’s wave function.

Pauling was intimately familiar with Heisenberg’s theory of quantum resonance as well as the hypotheses proposed by the British, American, and German contingent. Thus equipped, he began to construct a theory of his own that would prove crucial to building a “truer” understanding of molecular architecture and chemical bonding.

Pauling built and circulated his resonance theory in a series of papers that were published from 1931 to 1933. In them, he reasserted the ideas stated above, before emphasizing that

the actual normal state of such a molecule does not correspond to any one of the alternative reasonable structures, but rather to a combination of them, their individual contributions being determined by their nature and stability.

In other words, the individual isomers of a given molecule should not be viewed as existing in a state of rapid switching from one to another. Instead, a hybrid of every isomer is, in fact, the “true” form of the molecule.

The distinction that Pauling drew between rapidly switching isomers – which was known as tautomerism – and isomer hybrids was conceptually difficult for many scientists to grasp, but Pauling was able to cite experimental evidence in support of his theory. Namely, Pauling had found that resonating molecules existed at a much lower energy state than tautomerism would predict. Pauling believed that these lower energy states resulted in more stable molecules, an effect that lent support to the viability of resonance – as opposed to tautomerism – as an operating theory.

The experimental data continued to be important to Pauling as he pushed his theory forward. Some had argued that there was no real difference between resonance and tautomerism, because the classical understanding of tautomerization portrayed isomers as switching so rapidly as to be in a virtual hybrid state of their own accord. But the data showed that Pauling was describing something different and that, to use Pauling’s words, “it is easy to distinguish between the two.”

In a 1946 speech delivered to a private industry group, Pauling restated the basics of his theory using language that is useful for summarizing here. For a hypothetical molecule known to have two isomers, “neither the first structure nor the second structure represents the system. Instead, the molecule is ‘a combination’ of the two structures.” And importantly, when scientists

can write two structures, neither one actually represents the state of the molecule but both of them together represent the state of the molecule. The molecule is more stable actually than it would be if it had any of the structures that you can assign to it.

Benzene calculations in Pauling’s research notebook from June 1934

Though he faced early resistance, Pauling was eventually able to persuade most of his colleagues to align with his thinking on the theory of resonance, and he did so in part by using the theory to solve the elusive structure of benzene.

One of the reasons why chemists knew that Kekulé’s model of benzene was incorrect was because the observed energy level of the molecule was much lower than the number that Kekulé would have predicted. Something else, then, was causing the energy of benzene to be lower (and thus more stable).

Pauling’s theory suggested that resonating hybrids exhibit lower energies, and ultimately he was able to use his ideas to build a structure of the molecule that fit with the energy data. Once the model was accepted, the benzene breakthrough did much to secure resonance theory as a valuable and accurate tool for understanding molecular structure.

Pauling’s Final Guggenheim Fellowship

Pauling (with a broken foot) seated for a sculpture portrait session, 1966

[Pauling and the Guggenheim Foundation; part 17 of 17]

Linus Pauling’s relationship with the John Simon Guggenheim Memorial Foundation ended as it started: with Pauling as a Fellow.

Pauling’s first Guggenheim Fellowship, carried out in 1926 and 1927, helped to launch his career by putting him in touch with leading European quantum physicists. Pauling attempted to follow up on that success by applying for another fellowship, this time covering the summer of 1930 and focusing on the x-ray crystallographic methodology being pursued in Manchester by W. L. Bragg. Bragg was determining the structures of silicates and similar compounds, and Pauling sought to do the same thing with inorganic crystals.

Henry Allen Moe, Secretary of the Foundation, told Pauling that his 1930 application could not be renewed due to a lack of funds. Later, Pauling was looking for support for his immunology research and considered the Guggenheim as a possibility, but never followed through with a proposal. But some three decades later, once Pauling was no longer on the Foundation’s Committee of Selection, he would at last follow through once more.

Still image from one of Pauling’s 1957 lecture films on valence and molecular structure.

In 1957 the California Institute of Technology provided $17,000 for Pauling to make three fifty-minute color and sound films on the topics of molecular structure and valence. Once completed, the films proved very popular, screened by the National Science Foundation at about one hundred of their summer institutes for chemistry educators in 1959 alone. Pauling also helped colleague Richard Badger with a film on molecular vibration, though he was dissatisfied with the final result as the budget was very limited and he was still quite green as a producer. In 1960, with these experiences under his belt, Pauling proposed that he take another, more methodical approach to creating educational films about chemistry, and for that he approached the Guggenheim Foundation.

Though no longer on the Committee of Selection, Pauling was concerned that his position on the Guggenheim Advisory Board would disqualify him from consideration for a fellowship. Upon inquiry, the newly appointed Associate General Secretary of the Foundation, Gordon N. Ray, assured Pauling that there was no conflict and implored him not to resign from his board position.

With this guidance in hand, Pauling put together his application and sent it along. In doing so, Pauling reversed the circumstances of the previous thirty years: rather than serving as a reference for other applicants, Pauling this time sent in a list of those who might speak on his behalf. He was also compelled to put forth a strong case for his project, something for which he had been ably prepared by his many years on the Committee of Selection.

In his application, Pauling detailed a plan to make six ten- to fifteen-minute introductory films about molecular structure and valence. Once done, Pauling then proposed to research the films’ effectiveness by showing different versions to different students. The films would center around a short lecture, but the different edits would vary the amount of time the lecturer appeared on screen vis-à-vis models or animations. If the study identified a clearly superior production methodology, Pauling would then seek to prepare films for college and high school chemistry students.

As the project took shape in his mind, Pauling began to consult with a high-profile educational filmmaker, Syd Cassyd, the founder of the Academy of Television Arts and Sciences. From these conversations, Pauling developed a sense of how much it would all cost — roughly $36,000, with half going to Cassyd and the rest to production. To help cover those expenses, Pauling requested a stipend of $24,000 and offered to pay the remaining $12,000 himself.

Guggenheim Secretary Henry Allen Moe was happy to see Pauling’s application when it came in — a good sign that the proposal was headed for success. But a few months later, Pauling realized that he was drastically over-committed and ended up rescinding the application. In doing so, he expressed an intention to resubmit the following year, but this did not come to pass. However, five years later and after he had left Caltech for the Center for the Study of Democratic Intuitions in Santa Barbara, Pauling applied for a very different project.

By the mid-1960s, Pauling had developed a research interest in the structure of atomic nuclei, and though he had made progress on a theoretical model, he was uncertain whether or not his approach would pan out. To help bolster the work, he turned to the Guggenheim Foundation with a request for $36,000 over three or four years; funding enough to hire a theoretical physicist and to buy time on a computer to assist with needed quantum mechanical calculations. At the moment, Pauling had no funding at all to do work in physics.

In his application, Pauling explained that when nuclei with atomic masses greater than 230 – like uranium-235 and plutonium-239 – underwent low-energy fission, they split asymmetrically. The products of this asymmetric split were five hundred times more likely to have atomic masses of about 95 and 140 than they were to have equal masses. According to Pauling, the “alpha particle model,” which understood nuclei as consisting of particles equivalent to the nucleus of a helium-4 atom, was a good theory for explaining the lower mass, but less progress had been made in explaining the higher mass. To address this problem, Pauling had been working with a “large-cluster theory,” finding that it more completely explained the asymmetric fission along with other properties of nuclei.

Pauling thought that “helions” – an alternative term that he proposed to use in referring to alpha particles – composing the larger nuclei formed clusters that spanned the two shells that made up the nucleus. When grouped together in a nucleus, certain aggregate geometries of the clusters proved to be more stable than others, thus suggesting that some post-fission geometries were more probable than others.

Uranium and plutonium, for example, each had ten clusters, but if they were split evenly into two nuclei of five clusters, the resultant geometries would be unstable. Splitting instead into a four cluster nuclei and a six cluster nuclei would be much more stable and would match with experimental observations. While he felt that he had essentially worked out the theory, Pauling hoped to incorporate more mathematics into his model, in part to boost its appeal among physicists.

Image of Gordon N. Ray contemporary to his receipt of a Guggenheim Fellowship in 1941. Ray would later become President of the Foundation.

The Committee of Selection agreed that Pauling’s application had promise and, nearly forty years after his germinal trip to Europe, Pauling was once again a Guggenheim Fellow.

Pauling was one of 313 US and Canadian fellows in the class of 1966, a group that was selected from a pool of 1,869 applicants. The fellows were granted a total of $2,115,700, a sum that represented more than seven percent of the gross aggregate funding provided by the Foundation over the entirety of its 41-year history.

This major increase in annual awards was in part a reflection of a changing era within the Foundation, one marked by Henry Allen Moe’s 1963 retirement and Gordon Ray’s subsequent assumption of leadership. Overseeing a group of more than 300 awardees, Ray would not be able to meet with each fellow, as Moe had sought to do, but he took pains to reach out to Pauling with an invitation to get together the next time he was in New York. As he had previously been working without funds, Pauling was thrilled to have the support of the Foundation, and told Ray that he was already putting together three papers relevant to the award. Some of this research would be also presented at the National Academy of Sciences meeting in October.

As it happened, the Foundation did not provide the full amount that Pauling asked for, instead authorizing a total of $30,000 over three years. Management of the grant proved difficult as well. Despite the fact that he had not been on faculty at Caltech for nearly three years, Pauling asked that the first $8,000 be sent to the Institute for them to administer, and the next $10,000 sent to the Center for the Study of Democratic Institutions in Santa Barbara. Neither arrangement ended up proving convenient for Pauling, and he ultimately had the remainder of his award forwarded to him directly.

In the final year of his fellowship, Pauling sent copies of the articles that he had produced to Ray, along with a lament that the work had not received much attention. However, Pauling confided, Nobel Laureate Maria Mayer had suggested to him that one of the explanations that he had put forth for a certain problem was the only one that she had seen that made sense. Pauling continued to believe that if he could just integrate more mathematics into the theory, he could make a larger impression on the physics community.

Pauling’s successful 1966 Guggenheim application and subsequent award marked his last major interaction with the Guggenheim Foundation, an organization that he had helped to shape from its earliest years. With the bulk of this relationship behind him, Pauling still supplied comments on applicants in chemistry and biochemistry for the Committee of Selection into the mid-1960s, and submitted sporadic candidate references in the years that followed. His comments, as had always been the case, were concise and to the point, a quality that administrators like Henry Allen Moe and Gordon Ray unfailingly appreciated.