ON THE ALLYL-CYCLOPROPYL ISOMERISM OF SUBSTITUTED CATIONS - AN AML AND MNDO STUDY

Three series of cations (2-X-allyl cations (1), 1-X-cyclopropyl cations (2) and 1-X-isopropyl cations (3)) were investigated by both the MNDO and AMl quantum chemical methods. For pi-electron donators (X = NH2, OH, NHOH)) derivatives 2 are more stable than 1. The opposite is valid for derivatives with delta-electron acceptors (X = NO2, CHO, halogens). AMI values are closer to experimental or ab initio heats of formation than MNDO results. Therefore, by means of AMl only, reasonable ringstrain energies were obtained for 2, while the MNDO method failed in all investigated cases. It has been shown that the unknown 2-hydroxyaminoallyl cation is probably more stable than its cyclopropyl analogue.