A Mass Spectrometric Study of the Influence of Electronic and Stereochemical Factors on the Hofmann Elimination Process in Quaternary Ammonium Salts

Abstract

The mass spectra of the thermal decomposition products derived from the geometrical isomers of 2-phenylcyclohexyl- and 2-phenylcyclopentyltrimethylammonium salts together with their 2-d₁ analogs have been determined together with the rigid substrate, 3-endo-2-exo-norbornyltrimethylammonium bromide. It is found that the Hofmann elimination reaction is most favored when the departing groups or atoms have the anti coplanar relationship and that the abstracted hydrogen is exclusively the benzylic hydrogen. A series of 1-arylethyltrimethylammonium salts were also examined together with their 1-d₁ and 2-d₃ analogs. It was found that electron-donating substituents on the phenyl ring favor the Hofmann elimination process while electron withdrawers lead to the pyrolytic reaction of halide substitution at carbon.