Abstract Hydron exchange reaction rates, k exch M− 1 s− 1, using methanolic sodium methoxide are compared with gas-phase acidities, ΔG math image kcal/mol, for four 9- YPhenylfluorenes-9-i H, seven YC 6 H 4 C i H (CF 3) 2, seven YC 6 H 4 C i HClCF 3, and C 6 F 5 i H. Fourteen of the fluorinated benzylic compounds and pentafluorobenzene result in near unity experimental hydrogen isotope effects that suggest substantial amounts of ...