Molecular Geometry and Electronic Structure of Heptalentropones and Heptalendiones

The molecular geometries of 8-H-cycloheptatropone (I), 8-H- -cycloheptatropolone (II), 2-methoxy-8-H-cycloheptatropone (III), heptalen-1,8-dione (IV), 7-methoxy-heptalen-1,8-dione (V), 9-methoxy- heptalen-1,8-dione (VI) were fully optimized at lVIINDOj3 level. Heptalen-2,3-dione was also taken into account. The electronic structures of the above molecules were studied by means of INDOjS method and the importance of doubly excited configurations was tested at CNDO/S level. In all compounds a remarkable »single« and »double« bond alternation was found. Hydroxy and methoxy substitution affects the geometry of the ring where the substitution occurs whilst the unsubstituted ring unđergoes minor 01\u27 negligible changes. The electronic transitions agree well enough with the experimentally available absorption maxima; a strong transition is predicted in the neighborood of 200 nm. Several of these transitions can be correlated with those of tropone and tropolone: on the whole they are not, 01\u27 negligibly, affected by double excitations except those Iying in the range of 5 eV and the ones at 4.29 eV and 4.82 eV of heptalen-2,3-dione