Michael J. S. Dewar

Michael James Steuart Dewar (24 September 1918 – 10 October 1997) was an American theoretical chemist.

Education and early life Dewar was the son of Scottish parents, Annie Balfour (Keith) and Francis Dewar. He received the degrees of Bachelor of Arts, Master of Arts, and DPhil from Balliol College, Oxford.

Career and research Dewar was appointed to the Chair in Chemistry at Queen Mary College of the University of London in 1951.

Dewar's reputation for providing original solutions to vexing puzzles first developed when he was still a postdoctoral fellow at the University of Oxford. In 1945, he deduced the correct structure for stipitatic acid, a mould product whose structure had baffled the leading chemists of the day. It involved a new kind of aromatic structure with a seven-membered ring for which Dewar coined the term tropolone. The discovery of the tropolone structure launched the field of non-benzenoid aromaticity, which witnessed feverish activity for several decades and greatly expanded the chemists' understanding of cyclic π-electron systems. Also in 1945, Dewar devised the then novel notion of a π complex, which he proposed as an intermediate in the benzidine rearrangement. This offered the first correct rationalisation of the electronic structure of complexes of transition metals with alkenes, later known as the Dewar–Chatt–Duncanson model.

In the early 1950s, Dewar wrote a famous series of six articles on a general Molecular orbital Theory of Organic Chemistry, which extended and generalised Erich Hückel's original quantum mechanical treatments by using perturbation theory and resonance theory, and which in many ways originated the modern era of theoretical and computational organic chemistry. He did not however believe in the utility of Möbius aromaticity, introduced by Edgar Heilbronner in 1964, and now a flourishing area of chemistry.

He is known most famously for the development in the 1970s and 1980s of the Semi-empirical quantum chemistry methods, MINDO, MNDO, AM1 and PM3 that are in the MOPAC computer program, and which for the first time enabled the quantitative study of the structure and mechanism of reaction (transition state) of many real (i.e. large) systems.