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

Electron impact induced fragmentation patterns of 5H-dibenzb,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-dibenzb,f]azepine ( 2c ) based on the fragmentation of the trideuteriomethyl derivative ( 2d ). Side chain α-cleavage processes dominate the spectra of (5H-dibenzb,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-dibenzb,f]azepines 2a, 2c and 2e .