1,3 dipoles: Valence Bond study of their diradical character and reactivity toward alke(y)nes

B. Braïda^a, S. E. Galembeck^b, C. Walter^c, B. Engels^c, P. C. Hiberty^d

^aLaboratoire de Chimie Théorique - UMR 7616 UPMC & CNRS - Paris, France.
^bDepartamento de Química, Universidade de São Paulo, Brazil.
^cInstitut für Organische Chemie, Würzburg, Germany.
^dLaboratoire de Chimie Physique, Université Paris Sud XI, France.

Mercredi 29 Novembre 2017, 11^h00
bibliothèque LCT, tour 12 - 13, 4^ème étage

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Ozone and its sulfur-substituted isomers, prototype examples of 1,3-dipoles, are studied by means of the Breathing Orbital Valence Bond (VB) ab initio method, with the aim of estimating their controversial diradical characters. All 1,3-dipoles can be described in terms of three major VB structures, one diradical and two zwitterionic ones, out of the six structures forming a complete basis. It will be shown that the VB-calculated weight of the diradical structure of a molecule qualifies itself as a quantitative measure of diradical character, and not only an indicator of tendencies.[1] The reactivity of a selection of nine 1,3-dipoles toward ethylene and acetylene, as prototype reactions of 1,3-dipolar cycloaddition, will then be considered. It will be shown that the diradical character of 1,3-dipoles is a critical feature to favor 1,3-dipolar cycloaddition, and a new mechanism for 1,3-dipolar cycloaddition proposed.[2]
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References :
[1] B. Braïda, S. E. Galembeck and P. C. Hiberty, Submitted.
[2] B. Braïda, C. Walter, B. Engels and P. C. Hiberty J. Am. Chem. Soc. 2010, 132, 7631.