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

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.