Frontier molecular orbitals of heptalentropones, heptalendiones and their hydroxy and methoxy derivatives. An INDO/S study

The frontier molecular orbitals of heptalene (I), 8-H-cycloheptatropone (II), heptalen-3,8-dione (III), heptalen-1,8-dione (IV) and hepta- len-2,3-dione (V), calculated at INDO/S level, were analysed and compared with those of the corresponding hydroxy- and methoxy-derivatives. Hydroxy substitution effects are smaller than methoxy substitution ones but both groups increase the MO energies and causes remarkable changes in the MO features, except in V. In particular NHOMO and NNHOMO of mono-substituted Il and III are mainly localized on lateral molecular fragments. The energy difference between n orbitals, originating from negative and positive combinations of n atomic oxygen orbitals, is strongly affected by the distance between the carbonyl groups.In all molecules the unsubstituted C atoms adjacent to carbonyl or to substituent groups are always negatively charged