Acetone chemical ionization studies VIII: pyridine derivatives

Abstract

Acetone chemical ionization mass spectra of pyridine and 23 isomeric alkyl, dialkyl, amino, hydroxy, cyano and halo pyridines were studied. The formation of [M + H]⁺ ions and the adducts corresponding to [M + 43]⁺ and [M + 59]⁺ ions is controlled by the proton affinity of the substrate and the position of the substituent. The acetylation reaction is less pronounced in 2-substituted pyridines due to steric factors, except in amino and hydroxypyridines where the acetylated ion is stabilized through hydrogen bonding. Collision-induced dissociation (CID) spectra of [M + 43]⁺ ions of isomeric amino and hydroxypyridines suggest acetylation occurs mainly at the ring nitrogen.