Gas-phase specific reactivity of isomeric 1,3-benzodithiole anions: Tandemmass spectrometry and DFT theoretical studies

1,3-Benzodithiole dideuterated at the dithioacetal carbon atom has been ion ized in the chemical ionization source of a tandem triple quadrupole mass s pectrometer under NICI condition. Two isomeric anions are formed by abstrac tion of an o-phenylic proton or through abstraction of a deuteron. The frag mentation patterns occurring under dissociative collisions differ and confi rm the coexistence of two nonconverting carbanions. DFT calculations show t hat the dithioacetal anion is more stable than the phenylic. The nucleophil ic reactivity toward CS2 has been studied by collision-induced reactions in the collision cell of the tandem instrument. Both isomeric anion forms dis play characteristic fragmentations of the resulting [(M-H(D)) + CS2] adduct anions, demonstrating a difference in reactivity: the dithioacetal anion r eacts regioselectively at C and the o-phenylic at S, DFT calculations, perf ormed with the aim of rationalizing this observed difference and understand ing the formation of the diagnostic fragments, have been successful.