Correlation of extended Hückel theory with the chemical ionization reactions of cyclopropanes

Abstract

Semi-empirical molecular orbital calculations on the H⁺-methylcyclopropane reaction predict two dominant reaction channels: i, proton-addition to the C(1)–C(2) bond leading to a corner-protonated cyclopropane, and ii, hydride-abstraction from methyl giving H₂ and the cyclopropylcarbinyl carbocation; in solution the electrophilic addition pathway predominates, but in the gas phase under chemical ionization conditions both addition and abstraction pathways are not only competitive but their relative rates appear to be highly substituent-dependent.