Abstract σ-migration reactions are the important teaching content in basic chemistry courses for undergraduate chemistry majors, and the regioselectivity of the reactions is a key point to teaching and learning. In this paper, the H[1,j] σ migration reactions of a pentadiene derivative and their regioselectivity are discussed. Based on the Hückel molecular orbital method, the energy levels and molecular orbitals of π electrons in the simplest 4n+1 and 4n-1 linear conjugated systems are derived, which rationalizes the regioselectivity of the H[1,j] σ migrations of the pentadiene derivative under heating and light conditions. The structures and relative energies of the transition states of 1,3- and 1,5-H migrations of the pentadiene derivative are calculated by performing density functional theory calculations, and the calculated results verify that the pentadiene derivative prefers to perform the 1,5-H migration rather than the 1,3-H migration.
ZHAO Rong-Hao, ZHU Rong-Xiu, ZHANG Dong-Ju. Understanding the Regioselectivity of H[1,j]σ Migrations Using HMO Theory and Quantum Chemical Calculations[J]. Chinese Journal of Chemical Education, 2023, 44(16): 121-124.
