DEWAR, MICHAEL J. S.

(b. Ahmednagar, India, 24 September 1918, d. Gainesville, Florida, 10 October 1997), chemistry, computational chemistry, theoretical and experimental study of organic reaction mechanisms.

Dewar was one of the first, if not the first, organic chemist to master and apply molecular orbital theory. He pioneered many of the fundamental concepts that are now taken for granted, and over a period of four decades he developed and perfected the semi-empirical methods that are still in use. He developed a reputation for coming up with marvelously original and unorthodox ideas and for impeccable integrity.

Early Years and Career Summary . Dewar was born to Scottish parents in Ahmednagar, India, on 24 September 1918. His father was employed in the British government of India, the Indian Civil Service. Michael attended boarding school in England, having won a prestigious scholarship to Winchester College. In 1936, he entered Balliol College at Oxford, where he at first studied the classics. Before long, however, he developed a passion for organic chemistry. He earned a first-class honors undergraduate degree and his doctoral degree, and then stayed at Oxford as a postdoctoral fellow with Sir Robert Robinson in the Dyson Perrins Laboratory. Robinson left an indelible impression on the young chemist and remained his role model for the rest of Dewar’s life. It was at Oxford that Michael met Mary Williamson, a historian who later became well recognized as a scholar of English Tudor history. They married in 1944 and had two children, Robert and Steuart.

During the war, Dewar conducted defense research, serving as a temporary colonel. In 1945, Dewar became research director of the physical chemistry laboratory at Courtaulds in Maidenhead, near London. There he wrote The Electronic Theory of Organic Chemistry. Published in 1949, the work provided the first treatment of organic chemistry in terms of molecular orbital theory in a fashion accessible to the bench chemist.

In 1951, Dewar accepted a chair at Queen Mary College at the University of London, and he played an essential role in its development into a credible research program. He shocked British university circles when he moved to the University of Chicago in 1959. Soon thereafter, in 1963, he accepted the first Robert A. Welch chair at the University of Texas at Austin. He and his former student Rowland Pettit attracted many international and sabbatical visitors, transforming the university’s formerly undistinguished chemistry department into a pilgrimage site for those interested in theoretical chemistry or organic mechanisms. In 1980, along with his wife, he became a U.S. citizen. Dewar was elected to the National Academy of Sciences in 1983. He left Austin in 1989, moving to a half-time appointment at the University of Florida at Gainesville. He retired in 1994 and died in 1997.

Post-War Accomplishments . Dewar had a well-deserved reputation for finding original solutions to intractable problems. In 1945, when he was still a postdoctoral fellow at Oxford, he deduced the correct structure for stipitatic acid, a small organic molecule that had remained an enigma to the best organic chemists of the day. Dewar correctly deduced that it contained a new kind of seven-membered ring, for which he coined the term tropolone. He then suggested that another puzzling compound, the alkaloid colchicine, had a similar structure. This, too, turned out to be correct. The discovery of the nonbenzenoid but aromatic tropolone structure gave birth to the field of nonbenzenoid aromaticity, which witnessed feverish activity all over the world for several decades. It made a permanent contribution to the way in which chemists look at cyclic pi-electron systems. Dewar soon became a standard fixture on the international chemistry circuit, featured frequently as plenary lecturer at virtually every important international conference.

Also in 1945, Dewar introduced the concept of a φ complex in connection with his studies of the benzidine rearrangement. This notion automatically accounted for the ease of 1,2-shifts in carbocations and their absence in radicals and carbanions and explained the structure of “nonclassical” carbenium ions, which were just beginning to become well-known. Moreover, it offered a correct description of the electronic structure of complexes of transition metals with olefins, which then became known as the Dewar-Chatt-Duncanson model. At Courtaulds, Dewar developed a taste for the utility of models in practical chemistry. He measured the first absolute rate constants in a vinyl polymerization and in an autoxidation, and executed numerous other kinetic and mechanistic studies. In his free time, Dewar developed the concepts described in his first book, The Electronic Theory of Organic Chemistry(1949). This work started a revolution in the way in which organic chemists viewed their subject. By 1951, Dewar had developed a semiquantitative version of his theory for the practicing organic chemist who typically knew little or nothing about molecular orbitals. Unfortunately, his decision to publish it as a series of mathematical theorems in six back-to-back articles in the Journal of the American Chemical Society resulted in a wide appreciation of his erudition but little comprehension by the average organic chemist of the time. As a result, this approach, called “perturbational molecular orbital theory,” never became the everyday tool for practicing organic chemistry that it was designed to be. Even though the theory is clearly superior to the purely qualitative resonance structure theory, the latter remains more popular. Dewar was therefore regarded as a chemical genius whose

contributions, like Einstein's, were considered to be understandable to only a focused group of active theorists.

Queen Mary College Tenure . At Queen Mary College, Dewar continued his highly original work on the theory of organic chemistry. He tended to start controversies by adopting unorthodox and sometimes extreme views, for instance when he denied the existence of hyperconjugation. His work served to correct the simplistic descriptions accepted by many at the time and ultimately led to formulation of the more sophisticated pictures that are accepted in the early twenty-first century. In some cases, his strikingly novel views were ultimately recognized as literally correct, for instance his insistence that the classical inductive effect is insignificant and is best replaced by direct field effects, an insight that was based on his new experimental results.

Dewar’s experimental program was also extensive. His research group performed the first quantitative evaluation of reactivity in aromatic substitution, designed to test the semiquantitative perturbation molecular orbital theory he developed. Dewar solved the electronic structure of phosphononitrile chlorides, developed and characterized borazaro-aromatic compounds, examined the structure and properties of liquid crystals, and pioneered the now highly popular studies of self-assembled mono-layers of thiols on a metal surface. He built an electron paramagnetic resonance spectrometer for use in his research, at a time when it was just beginning to be recognized as useful in chemistry.

Chicago Interim . Dewar soon found the administrative duties associated with the chairing of a modern research-focused department burdensome. He solved the problem by giving up his chair at Queen Mary College and moving to the University of Chicago as a professor. Michael and Mary were already familiar with the United States from their 1957 half-year visit to Yale, which included an automobile trip around the country. During this visit they had met many American scientists, establishing many lasting friendships and collaborations. They were delighted with the country and with the spirit of its scientists, and were exuberant in their praise. Although he was elected a fellow of the Royal Society in 1960, Michael was adamant about remaining in the United States. Nevertheless, the Dewars spent each summer in England.

At Chicago, Dewar added new projects. He showed that charge transfer only makes a minor contribution to the stability of charge-transfer complexes, contrary to the general belief at the time. Most importantly, he created the field for which he is most likely best known: the development of increasingly sophisticated semi-empirical molecular orbital methods for organic chemistry. For this, he needed much more computer time than he could easily obtain at the University of Chicago, and this prompted his move to the University of Texas at Austin, with which his name is most strongly associated.

University of Texas: Career Peak . In Austin, his interests widened further. His experimental work now ranged from carbenium ions, semiconductors, and liquid crystals to nuclear quadrupole resonance and photoelectron spectroscopy; gradually, however, the attractions of sophisticated and highly useful applications of molecular orbital theory proved irresistible. A steady stream of world-renowned chemists found their way to Austin to engage Dewar’s insight to solve their own scientific problems. Ultimately, Dewar moved away from experiments to focus entirely on the improvement of semi-empirical molecular orbital methods. Although structure and many molecular properties were treated, his primary interest always was chemical reactivity, and he devoted most of his efforts to characterizing the structure and energetics of transition states of organic reactions.

Dewar has contributed much to current understanding of pericyclic reactions, hydrogen bonding, and sigma conjugation. Because the semi-empirical methods were computationally less demanding than the alternative ab initio methods, he was able to explore more realistic reaction models and to perform full geometrical optimizations of equilibrium and transition state geometries for large molecules well before others could do so. Toward the end of his active career, Dewar explored increasingly more complex phenomena, such as superconductivity, the structure of organometallics, and biological reactivity in enzymes and carbohydrates.

In the early twenty-first century, continued advances in computer technology and computer codes permitted ab initio calculations for large molecules at a level of sophistication that is far beyond anything that was available when Dewar developed his semi-empirical methods. Although this development rendered many applications of his semi-empirical approach obsolete, his models remained in use for very large molecules and for rapid preliminary scans. The power of modern computers permitted the development of a whole new family of semi-empirical methods based on density functional theory. One can easily imagine that if he had lived into the early 2000s, Dewar would have relished participating in the development of this current generation of parameterized methods, which have penetrated into all areas of chemistry, including nanoscience and molecular biology.

Teaching Methods . Dewar was also the quintessential teacher, cajoling and mentoring his students to maximize their growth as chemists. He insisted that they always stretch their goals to allow for understanding at the highest possible level. Few things pleased him more than the sudden look of understanding on the face of a previously unconvinced student. Although he was an exceedingly gentle man, he did not shy away from delivering necessary messages that his students and colleagues might not have wanted to hear, always in a spirit of inducing improvement. As a result, many of his students occupy important positions in the field.

Dewar was a formidable and witty debater who reveled in controversy and enjoyed nothing more than a good verbal match. He enjoyed expressing himself candidly, sometimes shocking others with his surprising ideas on all possible subjects. For example, he was known to declare with conviction that everyone ought to study Latin at an early age. He would give three reasons: (i) Latin is complex enough to teach children how to reason through intricate problems; (ii) because they tend to hate Latin, children learn at an early age how to cope with adversity; and (iii) in almost all cases Latin will be totally useless for them later, so it does not matter if they develop great aversion to it and fail to learn it. Another example is his rationale for breaking the speed limit while driving. He argued that accidents only occur when cars are moving on the road, never in the garage, and that it was best to minimize the time spent on the former activity and maximize the time spent on the latter. There were many others, presented with a disarming twinkle in his eye and a tongue in cheek.

Other Interests . Dewar’s wide interests in chemistry were matched by an even wider range of outside interests, from astronomy and geology to Asian cooking. In his youth, Dewar was an avid outdoorsman, but he had to give up rock climbing after a back injury. In his later years, his physical exercise consisted primarily of carrying large pitchers of Manhattans and martinis at the legendary parties the Dewars loved to give.

Dewar’s outspokenness pervaded all of his life and assured him a steady supply of adversaries. In his later years at Austin, he found it increasingly difficult to deal with the University of Texas’s overwhelming red tape. He finally decided to join the Quantum Theory Project at the University of Florida in Gainesville. Unfortunately, the disruption associated with this move preempted the completion of what might have been some of his finest work. The tragedy of Mary’s premature death by lung cancer— after her lifelong opposition to smoking—left him devastated. Some of the difficulty of this period is reflected in his memoirs, published by the American Chemical Society, “A Semi-Empirical Life,” which provides an uncharacteristically embittered and convoluted picture of a truly great man, who had been a warm and happy person.

Titles and Awards . Dewar’s professional recognition started early with his scholarships to Winchester and Balliol. He became a Gibbs Scholar in his second year at Oxford, the youngest ever. He received his first major award from the Chemical Society in 1954, in recognition of the influence of The Electronic Theory of Organic Chemistry and of the stunning 1952 series of articles in the Journal of the American Chemical Society that outlined the perturbational molecular orbital theory of organic chemistry. He was elected a Fellow of the American Academy of Arts and Sciences in 1966, and a member of the National Academy of Sciences soon after accepting U.S. citizenship. He was also elected to the Royal Society of Chemistry at age forty-two and was named an honorary Fellow of Balliol College (Oxford) and of Queen Mary and Westfield College (University of London).

Despite his distaste for flying, Dewar accepted thirty-two named lectureships and visiting professorships around the world and served as a stimulating consultant to industry both in the United States and abroad. His list of professional society awards serves as a nearly complete list of those available to organic chemists at the time:

Tilden Medal of the Chemical Society (1954)

Harrison Howe Award of the American Chemical Society (1961)

Robert Robinson Medal, Chemical Society (1974)

G. W. Wheland Medal of the University of Chicago (first recipient, 1976)

Evans Award, Ohio State University (1977)

Southwest Regional Award of the American Chemical Society (1978)

Davy Medal, Royal Society of London (1982)

James Flack Norris Award of the American Chemical Society (1984)

William H. Nichols Award of the American Chemical Society (1986)

Auburn–G. M. Kosolapoff Award of the American Chemical Society (1988)

Tetrahedron Prize for Creativity in Organic Chemistry (1989)

World Association of Theoretical Organic Chemists MedalChemical Pioneer Award, American Institute of Chemists (1990)

American Chemical Society Award for Computers in Chemistry (1994)

As a recipient of the Davy Medal, he is one of only six Americans to have been so selected. Dewar was especially proud of the achievements of his more than fifty doctoral students and sixty postdoctoral fellows, whose names are given in the more than six hundred referenced scientific papers and eight books that Dewar published.

BIBLIOGRAPHY

WORKS BY DEWAR

The Electronic Theory of Organic Chemistry. Oxford: Clarendon, 1949.

“A Review of the φ-Complex Theory.” Bulletin of the Chemical Society 18 (1951): C71–C79.

“A Molecular Orbital Theory of Organic Chemistry. I. General Principles.” Journal of the American Chemical Society 74 (1952): 3341–3345.

With H. N. Schmeising. “A Re-Evaluation of Conjugation and Hyperconjugation: The Effects of Changes in Hybridization of Carbon Bonds.” Tetrahedron 5 (1959): 166.

With Patrick J. Grisdale. “Substituent Effects. IV. A Quantitative Theory.” Journal of the American Chemical Society84 (1962): 3548–3553.

With Alice L. H. Chung. “Ground States of Conjugated Molecules. I. Semi-Empirical SCF MO Treatment and Its Application to Aromatic Hydrocarbons.” Journal of Chemical Physics 42 (1965): 756–766.

With N. C. Baird. “Ground States of Sigma-Bonded Molecules. IV. The MINDO Method and Its Application to Hydrocarbons.” Journal of Chemical Physics 50 (1969): 1262.

With Edwin Haselbach. “Ground States of Sigma-Bonded Molecules. IX. The MINDO/2 Method.” Journal of the American Chemical Society 92 (1970): 590.

With W. Thiel. “Ground States of Molecules. 38. The MNDO Method. Approximations and Parameters.” Journal of the American Chemical Society99 (1977): 4899–4907.

With E. G. Zoebisch, E. F. Healy, and J. J. P. Stewart. “AM-1: A New General Purpose Quantum Mechanical Molecular Model.” Journal of the American Chemical Society107 (1985): 3902–3909.

“The Semi-Empirical Approach to Chemistry.” International Journal of Quantum Chemistry 44 (1992): 427–447.

OTHER SOURCES

Michl, Josef, and Marye Anne Fox. “Michael J. S. Dewar.” National Academy of Sciences Biographical Memoirs. Vol. 77 (1999): 64–77. Washington, DC: National Academy Press.

Josef Michl

Marye Anne Fox