Michael J. S. Dewar
Encyclopedia
Michael James Steuart Dewar (born 24 September 1918) was a theoretical chemist
born in Ahmednagar, India
in 1918. He received the degrees of Bachelor of Arts
, Master of Arts, and DPhil
from the Balliol College, Oxford
). He was appointed to the Chair in Chemistry at Queen Mary College
of the University of London
in 1951. He moved to the University of Chicago
in 1959 and then to the first Robert A. Welch research chair at the University of Texas at Austin
in 1963. After a long and productive period there, he moved to the University of Florida
in 1989. He retired in 1994 as Professor Emeritus at the University of Florida. He died in 1997.
Dewar's reputation for providing original solutions to vexing puzzles first developed when he was still a postdoctoral fellow at Oxford University. In 1945, he deduced the correct structure for stipitatic acid, a mold 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 rationalization of the electronic structure of complexes of transition metal
s 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 Huckel
'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. Following Woodward
and Hoffmann
's suggestion of selection rules for pericyclic reactions, Dewar championed (concurrently with Howard Zimmerman) an alternative approach (pioneered by M. G. Evans) to understanding pericyclic reactivity based on aromatic and antiaromatic transition state
s. 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. This was illustrated in 1974 by computing (using the technique of energy minimisation
) the structure of a molecule as large as LSD
(with 49 atoms) at a quantum mechanical level (the calculation taking several days of the then state-of-the-art supercomputer
time, a CDC 6600). It is worth noting that in 2006, the equivalent calculation takes less than 1 minute on a personal computer. In 2006, the same structure computation can now be completed using high-level ab initio
or density functional procedures in less than two days, and semiempirical programs can be used to optimize the structures of molecules with perhaps 10,000 atoms.
He was a member of the International Academy of Quantum Molecular Science
.
Theoretical chemistry
Theoretical chemistry seeks to provide theories that explain chemical observations. Often, it uses mathematical and computational methods that, at times, require advanced knowledge. Quantum chemistry, the application of quantum mechanics to the understanding of valency, is a major component of...
born in Ahmednagar, India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
in 1918. He received the degrees of Bachelor of Arts
Bachelor of Arts
A Bachelor of Arts , from the Latin artium baccalaureus, is a bachelor's degree awarded for an undergraduate course or program in either the liberal arts, the sciences, or both...
, Master of Arts, and DPhil
Doctor of Philosophy
Doctor of Philosophy, abbreviated as Ph.D., PhD, D.Phil., or DPhil , in English-speaking countries, is a postgraduate academic degree awarded by universities...
from the Balliol College, Oxford
Balliol College, Oxford
Balliol College , founded in 1263, is one of the constituent colleges of the University of Oxford in England but founded by a family with strong Scottish connections....
). He was appointed to the Chair in Chemistry at Queen Mary College
Queen Mary, University of London
Queen Mary, University of London is a public research university located in London, United Kingdom and a constituent college of the federal University of London...
of the University of London
University of London
-20th century:Shortly after 6 Burlington Gardens was vacated, the University went through a period of rapid expansion. Bedford College, Royal Holloway and the London School of Economics all joined in 1900, Regent's Park College, which had affiliated in 1841 became an official divinity school of the...
in 1951. He moved to the University of Chicago
University of Chicago
The University of Chicago is a private research university in Chicago, Illinois, USA. It was founded by the American Baptist Education Society with a donation from oil magnate and philanthropist John D. Rockefeller and incorporated in 1890...
in 1959 and then to the first Robert A. Welch research chair at the University of Texas at Austin
University of Texas at Austin
The University of Texas at Austin is a state research university located in Austin, Texas, USA, and is the flagship institution of the The University of Texas System. Founded in 1883, its campus is located approximately from the Texas State Capitol in Austin...
in 1963. After a long and productive period there, he moved to the University of Florida
University of Florida
The University of Florida is an American public land-grant, sea-grant, and space-grant research university located on a campus in Gainesville, Florida. The university traces its historical origins to 1853, and has operated continuously on its present Gainesville campus since September 1906...
in 1989. He retired in 1994 as Professor Emeritus at the University of Florida. He died in 1997.
Dewar's reputation for providing original solutions to vexing puzzles first developed when he was still a postdoctoral fellow at Oxford University. In 1945, he deduced the correct structure for stipitatic acid, a mold 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
Tropolone
Tropolone is a derivative of tropone with a hydroxyl group in the 2-position.Two methods for the synthesis of tropolone are by bromination of 1,2-cycloheptanedione with N-bromosuccinimide followed by dehydrohalogenation at elevated temperatures and by acyloin condensation of the ethyl ester of...
. The discovery of the tropolone structure launched the field of non-benzenoid aromaticity
Aromaticity
In organic chemistry, Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. The earliest use of the term was in an article by August...
, 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
Benzidine
Benzidine, the trivial name for 4,4'-diaminobiphenyl, is the solid organic compound with the formula 2. This aromatic amine is a component of a test for cyanide and also in the production of dyes...
rearrangement. This offered the first correct rationalization of the electronic structure of complexes of transition metal
Transition metal
The term transition metal has two possible meanings:*The IUPAC definition states that a transition metal is "an element whose atom has an incomplete d sub-shell, or which can give rise to cations with an incomplete d sub-shell." Group 12 elements are not transition metals in this definition.*Some...
s with alkenes, later known as the Dewar-Chatt-Duncanson model
Dewar-Chatt-Duncanson model
The Dewar–Chatt–Duncanson model is a model in organometallic chemistry which explains the type of chemical bonding between an alkene and a metal in certain organometallic compounds. The model is named after Michael J. S. Dewar, Joseph Chatt and L. A...
.
Molecular orbital
In chemistry, a molecular orbital is a mathematical function describing the wave-like behavior of an electron in a molecule. This function can be used to calculate chemical and physical properties such as the probability of finding an electron in any specific region. The term "orbital" was first...
Theory of Organic Chemistry, which extended and generalised Erich Huckel
Erich Hückel
Erich Armand Arthur Joseph Hückel was a German physicist and physical chemist. He is known for two major contributions:*The Debye–Hückel theory of electrolytic solutions...
's original quantum mechanical treatments by using perturbation theory
Perturbation theory
Perturbation theory comprises mathematical methods that are used to find an approximate solution to a problem which cannot be solved exactly, by starting from the exact solution of a related problem...
and resonance theory
Resonance (chemistry)
In chemistry, resonance or mesomerism is a way of describing delocalized electrons within certain molecules or polyatomic ions where the bonding cannot be expressed by one single Lewis formula...
, and which in many ways originated the modern era of theoretical and computational organic chemistry. Following Woodward
Robert Burns Woodward
Robert Burns Woodward was an American organic chemist, considered by many to be the preeminent organic chemist of the twentieth century...
and Hoffmann
Roald Hoffmann
Roald Hoffmann is an American theoretical chemist who won the 1981 Nobel Prize in Chemistry. He currently teaches at Cornell University in Ithaca, New York.-Escape from the Holocaust:...
's suggestion of selection rules for pericyclic reactions, Dewar championed (concurrently with Howard Zimmerman) an alternative approach (pioneered by M. G. Evans) to understanding pericyclic reactivity based on aromatic and antiaromatic transition state
Transition state
The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest energy along this reaction coordinate. At this point, assuming a perfectly irreversible reaction, colliding reactant molecules will always...
s. He did not however believe in the utility of Möbius aromaticity
Möbius aromaticity
In organic chemistry, Möbius aromaticity is a special type of aromaticity believed to exist in a number of organic molecules. In terms of MO theory these compounds have in common a monocyclic array of molecular orbitals in which there is an odd number of out-of-phase overlaps which reveals the...
, introduced by Edgar Heilbronner
Edgar Heilbronner
Edgar Heilbronner was a Swiss German chemist. In 1964 he published the concept of Möbius cyclic annulenes, but the first Möbius aromatic was not synthesized until 2003....
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
Semi-empirical quantum chemistry methods
Semi-empirical quantum chemistry methods are based on the Hartree-Fock formalism, but make many approximations and obtain some parameters from empirical data. They are very important in computational chemistry for treating large molecules where the full Hartree-Fock method without the...
, MINDO
MINDO
MINDO, or Modified Intermediate Neglect of Differential Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Intermediate Neglect of Differential Overlap method of John Pople. It was developed by the group...
, MNDO
MNDO
MNDO, or Modified Neglect of Differential Overlap is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation. Similarly, this method replaced the earlier...
, AM1 and PM3
PM3 (chemistry)
PM3, or Parameterized Model number 3, is a semi-empirical method for the quantum calculation of molecular electronic structure in computational chemistry. It is based on the Neglect of Differential Diatomic Overlap integral approximation....
that are in the MOPAC
MOPAC
In computational chemistry, MOPAC is a popular computer program designed to implement semi-empirical quantum chemistry algorithms, such as MINDO, MNDO, AM1, PM3, PM5, and . It was largely written in the group of Michael Dewar at University of Texas, Austin...
computer program, and which for the first time enabled the quantitative study of the structure and mechanism of reaction (transition state
Transition state
The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest energy along this reaction coordinate. At this point, assuming a perfectly irreversible reaction, colliding reactant molecules will always...
) of many real (i.e. large) systems. This was illustrated in 1974 by computing (using the technique of energy minimisation
BFGS method
In numerical optimization, the Broyden–Fletcher–Goldfarb–Shanno method is a method for solving nonlinear optimization problems ....
) the structure of a molecule as large as LSD
LSD
Lysergic acid diethylamide, abbreviated LSD or LSD-25, also known as lysergide and colloquially as acid, is a semisynthetic psychedelic drug of the ergoline family, well known for its psychological effects which can include altered thinking processes, closed and open eye visuals, synaesthesia, an...
(with 49 atoms) at a quantum mechanical level (the calculation taking several days of the then state-of-the-art supercomputer
Supercomputer
A supercomputer is a computer at the frontline of current processing capacity, particularly speed of calculation.Supercomputers are used for highly calculation-intensive tasks such as problems including quantum physics, weather forecasting, climate research, molecular modeling A supercomputer is a...
time, a CDC 6600). It is worth noting that in 2006, the equivalent calculation takes less than 1 minute on a personal computer. In 2006, the same structure computation can now be completed using high-level ab initio
Ab initio quantum chemistry methods
Ab initio quantum chemistry methods are computational chemistry methods based on quantum chemistry. The term ab initiowas first used in quantum chemistry by Robert Parr and coworkers, including David Craig in a semiempirical study on the excited states of benzene.The background is described by Parr...
or density functional procedures in less than two days, and semiempirical programs can be used to optimize the structures of molecules with perhaps 10,000 atoms.
He was a member of the International Academy of Quantum Molecular Science
International Academy of Quantum Molecular Science
The International Academy of Quantum Molecular Science is an international scientific learned society covering all applications of quantum theory to chemistry and chemical physics. It was created in Menton in 1967. The founding members were Raymond Daudel, Per-Olov Löwdin, Robert G. Parr, John...
.