Semiempirical Calculation of 4-Dimethylaminopyridium, 2-Phosphorallylide and Their 1,5-Electocyclization Product

During the past decade, a trend has emerged of supporting the synthetic results and observed reactivities of different types of molecules by computational calculations. The electronic structure, aromaticities, conformations, and the process of inversion have been determined by carrying out their quantum chemical calculations. The ab initio calculations of some phosphines and their amino analogous having a pie orbital in alpha position have been reported earlier which reveal an interesting phenomenon of the donation of pie electron into the antibonding orbital of the P–X bond which has been termed as negative hyper-conjugation. These empirical calculations of pyridinium dichloro-phophinomethylides representing a system having a carbanion centre at the alpha position to the phophinomoiety have been recently carried out the first time by our research group.