REGIOSELECTIVITY OF DECHLORINATION OF DDT AND ITS METABOLITES IN MASS-SPECTROMETRY

DDT and several of its metabolites were synthesized with their aromati c chlorines enriched with Cl-37. The mass spectra of these compounds w ere recorded under electron impact and under methane positive-ion and electron-capture negative-ion chemical ionization. The regioselectivit y of the dechlorination reactions was determined by measurement of the relative proportions of the unlabeled aliphatic versus the labeled ar omatic chlorines in the various fragment ions observed. For all the al pha,beta-unsaturated compounds studied under electron impact ionizatio n, the regioselectivity is small, as both the aromatic and the aliphat ic chlorines are lost. Under positive-ion chemical ionization, the dec hlorination is highly regioselective, the aliphatic chlorines being al most exclusively lost. Under electron-capture negative-ion chemical io nization, the regioselectivity is also very high and the reactivity of the various chlorines is often controlled by the position of the arom atic chlorines.