Semiempirical molecular orbital calculation of azobenzene: stability study of isomers and mechanism of E/Z isomerization

Abstract

Semiempirical SCF-MO calculations are used to investigate the stability of isomers as well as the mechanism of E/Z isomerization of azobenzenes (1–6). MNDO and PM3 hamiltonians have shown the E isomer to be the most stable, in agreement with the experimental results. AM1, such as CNDO calculation, shows the Z isomer being more stable than the E isomer. This is contrary to all the experimental evidences. The isomerization pathway for interconversion between isomers of each compound is found to be through nitrogen inversion rather than N–N double bond rotation. This agrees well with the experimental mechanism suggested in n-hexane and gas phase. The calculated energy barrier for this process ranges from 20.4 to 31.5kcal/mol.