MASS-SPECTRA OF HALOGENATED ESTERS .9. METHYL-ESTERS OF 2-BUTENOIC ACIDS CONTAINING CHLORINE AND OR BROMINE ATOM(S)

The electron impact mass spectra of methyl esters of chloro‐, bromo‐, dichloro‐, bromochloro‐ and dibromo‐2‐butenoic acids (13 esters at all) have been investigated. Generally, the peaks due to the following fragments are abundant: M+·, [M  OCH3]+, [M  CH3OH]+·, [M  X]+, [M  OCH3  CO]+ or [M  COOCH3]+, [M  X  CH3OH]+ or [M  OCH3  HX]+, [M  OCH3  CO  HX]+, [M  OCH3  X  X]+ and [M  OCH3  CO  X  X]+. Characteristic for the 2‐ and 4‐halo isomers are the primary losses of a methyl radical and methanol, and for the 3‐halo isomers the loss of X· from M+·. Disparities between the spectra of the E and Z isomers are shown, the effect of position of halogen substitution being much more pronounced, as reported previously with the halogenated propenoic acid esters. Copyright © 1990 John Wiley & Sons, Ltd.