Cyclic sulphones. Part XI. Extensive delocalisation in benzo- and dibenzo-thiopyran SS-dioxide anions

Abstract

¹ H N.m.r. data obtained from the direct observation of benzo- and dibenzo-thiopyran SS-dioxide anions and of some methyl derivatives (I)–(IV) are consistent with a substantially trigonal configuration of the carbanion carbon and with extensive delocalisation of the negative charge within the rings. Evidence is also presented for the occurrence of ¹H n.m.r. time scale chemical exchange at the methylene group of 1-benzothiopyran SS-dioxide derivatives in methanol and in the presence of sodium methoxide.