Why is phenanthrene more stable than anthracene

Abstract

By means of a recently developed molecular-orbital-based method it is possible to estimate the energy effects of individual cycles, as well as pairs, triplets, etc. of cycles in polycyclic conjugated molecules. From these energyeffects one can better understand which structural details are responsible for the thermodynamic stability of the underlying molecule. In particular, it is possible to rationalize (in a quantitative manner) the causes of differences in the thermodynamic stability of isomers. Such an analysis is here performed on the two isomeric benzenoid hydrocarbons with three hexagons – anthracene and phenanthrene.