Electron‐impact induced fragmentation of 2‐substituted pyridines and picolines

Abstract

Abstract The fragmentation patterns obtained upon electron impact on 2‐nitro‐, 2‐chloro, and 2‐aminopyridines, as well as those of the corresponding 3‐, 4‐, 5‐ and 6‐picolines were examined. There was considerable departure from those patterns reported for the corresponding benzenoid derivatives. Although the molecular ion from 2‐nitro‐3‐picoline did not show fragment ions attributable to an “ortho‐effect” (unlike o ‐nitrotoluene), those from 2‐chloro‐ and 2‐amino‐3‐picolines did show a loss of HCl and NH 3 , respectively. Quite unexpectedly the ions from 2‐chloro‐ and 2‐amino‐6‐picolines also lost HCl and NH 3 . Such meta ‐eliminations for the 2‐substituted‐6‐picolines are postulated to be preceeded by either hydrogen or methyl migration. The mass spectra of 2‐pyridone, 2‐pyridthione and their respective 3‐, 4‐, 5‐ and 6‐methyl analogs were also studied. The primary fragmentations of the 2‐pyridones were as expected from those reported in the literature. The ions from 3‐ and 6‐methyl‐2‐pyridones lost water also, the former being another example of an “ ortho ‐effect” observed in this series. Of the thiones, the fragmentations of 3‐methyl‐2‐pyridthione proved most unique since its molecular ion showed besides the loss of HS, the pronounced elimination of H 2 S, the latter presumably due to an “ortho‐effect.” Figures are presented to illustrate the patterns and metastable ions are indicated when found for the transitions discussed.