A novel hydrogen rearrangement of bifunctional o‐xylylene derivatives in chemical ionization mass spectrometry

Abstract

A novel hydrogen rearrangement reaction was found in benzyl ions that have a (benzyl) k -Z C H -group (Z=O or N) at their ortho position. From deuterium labeling experiments, mass analyzed ion kinetic energy spectra with collisional activation, and examination of structure-peak intensity correlation, a mechanism is proposed which involves a direct transfer of hydrogen (hydride) to the structurally remote but spatially close cationic center. The possibility of an alternative, less likely mechanism including an iodneutral complex and/or a proton-bridged complex has also been discussed. I IDuring the course of our recent work on chemical ionization mass spectrometry of bifunctional ~o m p o u n d s ,~-~ we had occasion to measure the chemical ionization mass spectrum of o-[methoxymethyllbenzyl amine (o-CH,0CH2-C6H4--CH2NH2) ( 1)6 and encountered a novel hydrogen rearrangement reaction, which involves a direct transfer of hydrogen (hydride) to the structurally remote but spatially close cationic center. A recent paper by Italian workers' on similar reactions prompted us to report our own results at this stage of the continuing work. EXPERIMENTAL Mass spectraAll mass spectra were measured with either a Shimadzu LKB (Tokyo, Japan) 9000A mass spectrometer/ GCMS-PAC-90 computer system or Shimadzu 9020 D F reversed geometry mass spectrometer with Shimadzu GCMS PAC 1100 S data processing system. The ion source temperature for chemical ionization conditions was 230°C and an accelerating voltage of 3.5 kV was used. The total emission current was 120 pA and the electron energy was 150 eV. Collision-induced dissociation (CID) spectra were obtained by using helium as the collision gas, at a pressure leading to a reduction of the main beam intensity of 30%.