Electron‐impact induced skeletal re‐arrangement of 2‐methoxy‐3‐methylpyrazine and 2‐methylthio‐3‐methylpyrazine

Abstract

AbstractThe mass spectra of 2‐methoxy‐3‐methylpyrazine (I), 2‐methoxy‐6‐methylpyrazine (II), 2‐methylthio‐3‐methylpyrazine (III) and 2‐methylthio‐6‐methylpyrazine (IV), are given and the major fragmentation pathways discussed. The novel loss of H2O from the molecular ion of I and the corresponding loss of H2S from the molecular ion of III indicate that a skeletal rearrangement takes place in the molecular ion preceding the expulsion of H2O and H2S. Proposed mechanisms for this behavior are discussed with evidence being drawn from accurate mass measurement, metastable ions, and deuterium and carbon‐13 labeling of the methoxy group. The absence of ions in the spectra of II and IV corresponding to the loss of H2O and H2S from these molecular ions clearly indicates that the position of the methyl group with respect to the methoxy group, or the methylthio group is in‐timately involved in this mechanism.