Abstract:

The molecular orbitals of transition states of 1, 2-shift and 1, 4-shift of carbanion were calculated using the density functional theory (DFT) method. It was found that the migration atom carried positive charge and the rest of the carbanion became a double carbanion. In the transition state of 1, 2-shift, the phase of HOMO of the double carbanion doesn't match that of LUMO of the migration atom. However, in the transition state of 1, 4-shift, the phase of HOMO of the double carbanion matches that of LUMO of the migration atom. So the 1, 2-shift of carbanion is an orbital symmetry prohibited reaction and the 1, 4-shift of carbanion is an orbital symmetry permitted reaction. The calculation in this paper can afford a valuable reference for the teaching of advanced organic chemistry.

Key words: Carbanion, Rearrangement, Orbital symmetry, Chemical calculation