On the Alternation Effect in Substituted Indolizines and Their Aza-analogs

The SINDO1 method is used to calculate charge distribution and total energies in the series of isomeric nitro- and methoxy-substituted indolizines, azaindolizines, and N-methylazaindolizinium cations. The influence of donor and acceptor substituents on the total energy and charges may be treated according to the simple alternation rule. In the series of isomers (substituted or azaindolizines) the lower energies are observed for those molecules, where acceptor substituents are arranged consonant to the polarity of the chain N-C(5)-C(6)-C(7)-C(8)-C(9)-C(1)-C(2)-C(3) of the indolizine. The results are used to treat known peculiarities of ring opening/transformation of indolizine and its aza-derivatives. It is proved that the energies of C(3) and C(5) adducts of isomeric azaindolizines with hydroxyl anion follow the same alternation pattern.