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Mechanism of electron impact ionization‐induced halogen elimination from 2‐methyl‐2‐bromosuccinates
Author(s) -
Bornstein D.,
Mandelbaum A.,
Vidavsky I.,
Domon B.,
Mueller D. R.,
Richter W. J.
Publication year - 1993
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210280315
Subject(s) - chemistry , deuterium , halogen , electron ionization , methyl group , dissociation (chemistry) , methyl radical , labelling , protonation , medicinal chemistry , ion , methyl acetate , photochemistry , stereochemistry , ionization , organic chemistry , radical , group (periodic table) , methanol , biochemistry , alkyl , physics , quantum mechanics
The electron impact‐induced halogen elimination from 2‐methyl‐2‐bromosuccinates occurs only in the one of the two isomeric methyl ethyl esters in which the ethoxycarbonyl group is remote from the halogen, in analogy with the corresponding previously reported halosuccinates. However, the occurrence of debromination in dimethyl 2‐methyl‐2‐bromosuccinate contrasts with the behaviour of dimethyl bromosuccinate, indicating different mechanisms for this process in the two systems. Collision‐induced dissociation (CID) and deuterium labelling studies led to the conclusion that a hydrogen transfer from the 2‐methyl group to a carbonyl precedes the elimination of Br˙ from dimethyl 2‐methyl‐2‐bromosuccinate, resulting in a protonated dimethyl itaconate structure for the [M – Br] + ion. An analogous process is the major route leading to [M – Br] + ion from 1‐methyl‐4‐ethyl 2‐methyl‐2‐bromosuccinate. In this case deuterium labelling and CID measurements indicated a significant contribution of methyl ethyl citraconate and possibly mesaconate owing to partial operation of a mechanism similar to that reported for 1‐methyl‐4‐ethyl 2‐bromosuccinate.