Rep:Mod:Phys3xc1412

Cope Rearrangement

The Cope rearrangement of 1,5-hexadiene is a [3,3]-sigmatropic cycloaddition. This study will focus on the transition structure of the above reaction. According to The Woodward-Hoffmann rules, the reaction go through a Hückel transition state. The transition structure can be of either 'chair' or 'boat' conformation.

Optimise Starting Material And Products

First the reactants, 1.5-hexadiene with an ‘anti’ linkage was optimised at HF/3-21G level of theory using Hartree Fock method. Total energy of -231.691a.u. was obtained. By comparing to Appendix1, it was determined that this structure has the same energy as anti-2 configuration. The point group for this molecule has determined to be Ci.

Then 1,5-hexadiene with a ‘gauche’ linkage has also be optimised at the same theory level and using the same method. Total Energy was determined to be -213.687a.u, which shows agreement with appendix1. Gauche configuration. This molecule has a C2 symmetry.

A few more optimisations have been done and all structures in Appendix 1 has been found. It was determined that the ‘anti1’ structure has the lowest energy. This energy(-231.693 a.u.) will be used to calculate activation energy in the next few steps.