Deprotonation of 9-(trimethylsilyl)fluorene (2) by CH3SOCH2-K+ in dimethyl sulfoxide (DMSO) is accompanied by desilylation, whereas the more sterically hindered 9-(triethylsilyl)- and 9-(triphenylsilyl)fluorenes (3 and 4) undergo only deprotonation. Compounds of 2 and 3 are each 2.2 kcal/mol more acidic than fluorene in DMSO, and 4 is 5.9 kcal/mol more acidic. The homolytic bond dissociation enthalpies (BDEs) of the acidic C-H bonds in 2, 3, and 4 are stronger by an average of 1.9 kcal/mol than that of fluorene (BDE=79.5). The carbon acids PhSO(2)CH(2)SiMe(3) and PhSO(2)CH(2)SiPh(3) are 4.2 and 10.5 kcal/mol more acidic, respectively, in DMSO than is PhSO(2)CH(3), and the BDEs of their acidic C-H bonds are estimated to be 0.5 kcal/mol stronger and 1.6 kcal/mol weaker, respectively. PhSO(2)CH(SiMe(3))(2) is a 12.5 kcal/mol stronger acid than PhSO(2)CH(3), and the BDE of its acidic C-H bond is estimated to be 2.5 kcal/mol weaker. The carbon acid PhS(O)(=NSO2C7H7)CH(SiMe(3))(2) is 8.1 kcal/mol stronger than PhS(O)(=NSO2C7H7)CH3, and the BDE of its acidic C-H bond is 3.3 kcal/mol weaker. Here there is a sizable increase in acidity but a relatively small effect : on BDE despite the introduction of two SiMe(3) groups at the acidic site. These large acidifying effects accompanied by little or no effect on the BDE are characteristic of a polarizability effect.