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Aromatic versus diradical character in the transition states of the Cope rearrangements of 1,5-hexadiene and its cyano derivatives.

Blavins, J.J., Cooper, D.L. and Karadako, P.B. (2004) Aromatic versus diradical character in the transition states of the Cope rearrangements of 1,5-hexadiene and its cyano derivatives. Journal of Physical Chemistry A, 108 (1). pp. 194-202. ISSN 1089-5639

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Abstract

Using geometries optimized at the (U)B3LYP/6-31G(d) level, ab initio modern valence bond calculations are used to quantify directly the relative importance of aromatic, diradical, and bisallyl contributions to the transition states of gas-phase Cope rearrangements of 1,5-hexadiene and various cyano derivatives. The main effect on the character of the transition state of substituting radical-stabilizing cyano groups is found to be indirect, via the geometry, with shorter interallyl separations favoring diradical character and larger ones favoring aromaticity. In the case of the parent Cope reaction, the weights of the aromatic and diradical components are comparable at the transition state. We find that bisallyl character only becomes important for transition states with rather large interallyl

Item Type: Article
Institution: The University of York
Academic Units: The University of York > Chemistry (York)
Depositing User: York RAE Import
Date Deposited: 16 Apr 2009 14:29
Last Modified: 16 Apr 2009 14:29
Published Version: http://dx.doi.org/10.1021/jp036660i
Status: Published
Publisher: American Chemical Society
Identification Number: 10.1021/jp036660i
URI: http://eprints.whiterose.ac.uk/id/eprint/6795

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