The substituent effect on the single and double hydrogen atom transfer reactions in para‐substituted benzoic acid isobutyl esters

Abstract

The substituent effect on the single and double hydrogen atom transfer reactions in para-substituted benzoic acid isobutyl esters has been investigated by electron impact mass spectrometry. Electron-donahg substituents favour formation of the [M-C4&]+' ion generated by single hydrogen atom transfer reaction (McLafferty rearrangement), whereas electron-withdrawing substituents favour formation of the [M-C&]+ ion generated by double hydrogen atom transfer reaction. In the case of the latter compounds, the m/z% ([C&]+.) ion, which is generated by single hydrogen atom transfer reaction with charge migration, is very intense, while in the former compounds, the m/z 56 ion is very weak. These observations can be reasonably explained on thermochemid grounds based on the sum of the standard heats of formation of the fragments. ~~