THE REARRANGEMENT IN THE MOLECULAR ION OF 2-(2'-METHOXYPHENYL)BENZOIC ACID

The molecular ion of 2-(2'-methoxyphenyl)benzoic acid, formed by electron impact at 70 eV, loses CH3O°, CH3OH and other small fragments presumably from the syn conformation. It also gives rearrangement ions at m/z 94, C6H6O, and at m/z 135, C8H7O2, in which part of a functional group in one ring has been transferred to the other ring. To identify the rings, the one that contained the methoxy group was labelled with bromine. The bromine atom was lost from many fragment ions in the 70-eV mass spectrum, but the 10-eV spectrum provided sufficient evidence to propose a mechanism for the rearrangement which occurs in the anti conformation of the molecular ion. Hydrogen-deuterium exchange between labelled functional groups appears to proceed normally. © 1990 ASEG.