Mass spectral fragmentation patterns of heterocycles. IX . Investigation of fundamental processes in 5H‐dibenz[b,f]azepines and dihydro‐5H‐dibenz[b,f]azepines

Abstract

AbstractElectron impact induced fragmentation patterns of 5H‐dibenz[b,f]azepine (1a), 10,11‐dihydro‐5H‐dibenz‐[b,f]azepine (2a) and some 5‐substituted derivatives were investigated using metastable ion studies, exact mass measurements and deuterated analogues. Studies employing 4,6‐dideuterio derivatives indicate that the formations of ions of m/e 191, 180, 167, 166 and 152 are associated with a variety of skeletal reorganization processes accompanied by hydrogen (or deuterium) transfers involving peri (4‐ or 6‐) hydrogen (or deuterium) atoms. The methyl radical expelled in the formation of the M‐15 ion in the spectrum of 2a is derived from the benzylic carbon(s). A similar process is, in part, responsible for the expulsion of a methyl radical from the molecular ion of 5‐methyl‐10,1 1‐dihydro‐5H‐dibenz[b,f]azepine (2c) based on the fragmentation of the trideuteriomethyl derivative (2d). Side chain α‐cleavage processes dominate the spectra of (5H‐dibenz[b,f]azepine‐5‐yl)acetaldehyde diethylacetal and its 10,11‐dihydro analogue. Hydrogen atom transfer processes involving benzylic hydrogen atoms occur in the fragmentation of the 10,11‐dihydro‐5H‐dibenz[b,f]azepines 2a, 2c and 2e.