AB-INITIO STUDY OF AZIRIDINES AND DIAZIRIDINES - NITROGEN INVERSION, RING-OPENING, AND THERMOCHEMISTRY

The chemistry of a series of aziridines and diaziridines, including th e parent compounds aziridine and diaziridine and several methyl-substi tuted analogues, is studied by high-level ab initio methods. The elect ronic structure methods employed include second-order Moller-Plesset p erturbation theory (MP2), the coupled cluster singles and doubles meth od with a perturbative correction for connected triple substitutions [ CCSD(T)], and the Brueckner doubles method with analogous corrections for triple and quadruple substitutions [BD(TQ)]. Computations are carr ied out with basis sets ranging in size and quality from 6-31C and cc -pVDZ to cc-pV5Z. Stationary points for nitrogen inversion are located on the ground-state potential energy surfaces, and high-level barrier s to nitrogen inversion are obtained. Thermodynamic activation paramet ers and deuterium isotope effects are computed for nitrogen inversion and compared with experimental results. The energetics are investigate d for the conrotatory ring opening of aziridine, which produces an imm onium ylide. Finally, accurate values are determined for the heat of f ormation of aziridine and diaziridine by application of high-level foc al-point thermochemical analyses.