The formation and characterization of three-membered ring carbanions in the gas phase: An experimental and theoretical investigation of the conjugatebases of thiirane, thiirane S-oxide, and thiirane S,S-dioxide

Deprotonation of thiirane, thiirane S-oxide, and thiirane S,S-dioxide was c arried out in the gas phase, and the resulting anions were studied through a series of ion-molecule reactions. The cyclic conjugate bases of thiirane (Ib) and thiirane S,S-dioxide (3a) are formed whereas a facile ring opening isomerization to vinyl sulfenate anion (2d, CH2=CHSO-) is observed in the thiirane S-oxide case. Vinyl thiolate, the rearrangement product of the con jugate base of thiirane, also is obtained. Proton affinities were determine d for Ib; 2d, and 3a. High-level ab initio calculations were also carried o ut, and the results compared with those obtained from experiment. Orbital a rguments are advanced to explain the relative barriers to ring opening for the three anions of interest.