Lionel Salem (born 5 March 1937, Paris) is a French

theoretical chemist Theoretical chemistry is the branch of chemistry which develops theoretical generalizations that are part of the theoretical arsenal of modern chemistry: for example, the concepts of chemical bonding, chemical reaction, valence, the surface ...

, former research director at the

French National Centre for Scientific Research The French National Centre for Scientific Research (french: link=no, Centre national de la recherche scientifique, CNRS) is the French state research organisation and is the largest fundamental science agency in Europe. In 2016, it employed 31,637 ...

(CNRS), retired since 1999. He is a member of the

International Academy of Quantum Molecular Science The International Academy of Quantum Molecular Science (IAQMS) 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 wer ...

which named him its annual award winner in 1975 ''for his work on photochemical processes and on chemical reaction mechanisms.'' . He has contributed to the theories of forces between molecules, of conjugated molecules, of organic

reaction mechanism In chemistry, a reaction mechanism is the step by step sequence of elementary reactions by which overall chemical change occurs. A chemical mechanism is a theoretical conjecture that tries to describe in detail what takes place at each stage of ...

s and of

heterogeneous catalysis In chemistry, heterogeneous catalysis is catalysis where the phase of catalysts differs from that of the reactants or products. The process contrasts with homogeneous catalysis where the reactants, products and catalyst exist in the same phase. Ph ...

. He developed the electronic theory of diradicals, as well as the concepts of

diradical In chemistry, a diradical is a molecular species with two electrons occupying molecular orbitals (MOs) which are degenerate. The term "diradical" is mainly used to describe organic compounds, where most diradicals are extremely reactive and in ...

and

zwitterion In chemistry, a zwitterion ( ; ), also called an inner salt or dipolar ion, is a molecule that contains an equal number of positively- and negatively-charged functional groups. : With amino acids, for example, in solution a chemical equilibrium wil ...

ic states. In 1968 he described the energy change for the approach of two molecules as a function of the properties of the orbitals of the two molécules; this approach, pursued independently by

Gilles Klopman Gilles Klopman (February 24, 1933 – January 10, 2015) was the Charles F. Mabery Professor of Research in Chemistry, Oncology and Environmental Health Sciences Director of the Laboratory for Decision Support Methodologies at Case Western Reserve U ...

, led to the

Klopman-Salem equation In the theory of chemical reactivity, the Klopman-Salem equation describes the energetic change that occurs when two species approach each other in the course of a reaction and begin to interact, as their associated molecular orbitals begin to overl ...

and the theory of frontier orbitals. He is the author of several books on chemical subjects, including ''The Molecular Orbital Theory of Conjugated Systems'' (1966), ''The Organic Chemist's Book of Orbitals'' (with William L. Jorgensen, (1973)), ''The Marvelous Molecule'' (1979) and ''Electrons in Chemical Reactions'' (1982).

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{{DEFAULTSORT:Salem, Lionel Theoretical chemists 20th-century French chemists Living people 1937 births