Mass spectra of halogenated esters 6—Methyl esters of some trihalogenated propanoic and butanoic acids

The mass spectral fragmentation of trihalogenated methyl esters, formed in the reactions of monochlorinated methyl propenoates and 2‐butenoates with Cl 2 , BrCl and Br 2 , have been investigated. In most cases α‐cleavage gives the base peak, [COOCH 3 ] + , the peaks originating from the subsequent losses of one or two halogen atoms also being abundant. The primary loss of a halogen atom is more prominent in the C 4 derivatives, Br˙ and Cl˙ being preferentially lost from the 2‐ and 3‐positions, respectively. The McLafferty rearrangement yields in one case the base peak; the 2‐halo compounds could in general be distinguished by that fragmentation. Typical for all 2‐bromo‐substituted methyl butanoates studied is the base peak, [C 3 H 3 ] + , at m / z 39, and for some 3‐halo compounds the peaks at m / z 95, [C 2 H 4 ClO 2 ] + and 139, [C 2 H 4 BrO 2 ] + .