Chapter 30.4, Problem 4P

Interpretation Introduction

Interpretation:

Product of the photochemical cyclization of (2E,4Z,6E)-2,4,6-octatriene. Of (2E,4Z,6Z)-2,4,6-octatriene.

Concept introduction:

In photochemical reactions, the orbitals of the HOMO of the excited state to determine the course of the reaction. The excited state HOMO has the opposite orientation of the outermost p orbitals compared to the HOMO of the ground state. As a result, the method of ring closure of a photochemical electrocyclic reaction is opposite to that of a thermal electrocyclic reaction for the same number of pie bonds.

Photochemical electrocyclic reactions occur in a conrotatory fashion for a conjugated polyene with an odd number of pie bonds.