Geometries of the first triplet and first singletn-π* excited states of benzaldehyde have been optimized using thesindo 1 molecular orbital wave-function (with CI) and the Newton-Raphson method. The triplet excited state geometry of the molecule is found to be appreciably non-planar whereas that of the singlet excited state is planar. A crossing of molecular orbitals occurs in going from the ground state equilibrium geometry to the triplet and singletn-π* excited state equilibrium geometries. Existence of the para-directing effect of the singletn-π* transition for electronic charges found in an earlier work is confirmed by the present work. The tripletn-π* excitation rearranges electronic charges mainly on the CHO group. It is found that the dipole moment of the molecule would appreciably increase following the singletn-π* excitation whereas the same would appreciably decrease following the tripletn-π* excitation.

Geometries of the ground, first triplet and first singlet excited states of a hydrohydroxide of uracil have been optimized using the SINDO 1 SCF molecular orbital method in conjunction with configuration interaction. The first triplet and first singlet transitions of the molecule are found tc/be of (π-sp*) type which shows their orbitally forbidden character. Thus an explanation as to why the adducts formed by the addition of H₂O, hydroxylamine, bisulphite etc at the CC double bonds of pyrimidines do not absorb in the characteristic 260 nm region has been provided.