Rotational barriers in azobenzene and azonaphthalene.

Theoretical predictions of rotational barriers for pi-conjugated substituents of aromatic rings sometimes significantly overestimate the corresponding experimental values. In this work, the rotational barriers in benzaldehyde, azobenzene, and azonaphthalene are studied by DFT calculations employing a variety of exchange-correlation functionals and basis sets. The results for benzaldehyde and azobenzene agree with previously published theoretical values. For azonaphthalene, 10 unique minima and corresponding rotational barriers have been found. The ability to distinguish minima connected by rotational barriers opens an opportunity for a detailed experimental study of rotational barrier heights in substituted aromatics.