A B3LYP study of the effects of phenyl substituents on 1,5-hydrogen shifts in 3-(Z)-1,3-pentadiene provides evidence against a chameleonic transition structure

Shuichi Hayase; David A Hrovat; Weston Thatcher Borden

doi:10.1021/ja048708r

A B3LYP study of the effects of phenyl substituents on 1,5-hydrogen shifts in 3-(Z)-1,3-pentadiene provides evidence against a chameleonic transition structure

J Am Chem Soc. 2004 Aug 18;126(32):10028-34. doi: 10.1021/ja048708r.

Authors

Shuichi Hayase¹, David A Hrovat, Weston Thatcher Borden

Affiliation

¹ Department of Chemistry, Box 351700, University of Washington, Seattle, Washington 98195-1700, USA.

PMID: 15303877
DOI: 10.1021/ja048708r

Abstract

The effects of one or two phenyl substituents on the activation enthalpy for a 1,5-hydrogen shift in 3-(Z)-1,3-pentadiene (1) and on the geometry of the transition structure (TS) have been investigated by B3LYP/6-31G calculations. The phenyl-substituent effects on the experimentally measured activation enthalpies are predicted to be sizable, spanning a range of nearly 10 kcal/mol. However, if differences between steric effects in the transoid isomers of the reactants are factored out by comparing the activation enthalpies in the cisoid conformers, the electronic components of the phenyl-substituent effects on both the barrier heights and the TS geometries are found to be quite modest in size. Unlike the TS in the Cope rearrangement, the TS for a 1,5-hydrogen shift in 1 is not highly variable in nature, and the reason the 1,5-hydrogen shift TS is not chameleonic is discussed.