AbstractThe equilibrium acidities, pKHA, of 18 dialkyl malonates, five alkyl 2‐cyanoacetates and nine malononitriles and the oxidation potentials of their conjugate anions,EOX(A−), were measured in dimethyl sulfoxide solution. The homolytic bond dissociation enthalpies (BDEs) of their acidic C–H were estimated by combining their pKHAandEOX(A−) values. The pKHAvalues of the dialkyl malonates were found to increase from 15·9 to 16·4 to 18·4 as the dialkyl groups were changed from dimethyl to diethyl to di‐tert‐butyl, but theBDEs of the acidic C–H bonds remained constant [95·3±0·3 kcal mol−1] (1 kcal = 4·184 kJ). Introduction of methyl, ethyl, isopropyl andtert‐butyl groups into the 2‐position of diethyl malonate caused the equilibrium acidities to increase by 2·0, 2·4, 3·8 and 8·0 pKHAunits, respectively, and theBDEvalues to decrease by 4·4, 3·7, 2·5 and 0·8 kcal mol−1, respectively. Introduction of a phenyl group into the 2‐position of diethyl malonate had no effect on the acidity, but weakened the acidic C–H bond by 10 kcal mol−1. The effects on acidity andBDEof introducing 3,4,5‐ (MeO)3C6H2CO, CF3, Me3N+,c‐C5H10N,p‐MeC6H4,p‐NO2C6H4, PhO, F andc‐C5H5N+groups into t