The accurate O-H bond dissociation enthalpies for a series of meta and para substituted phenols (X-C6H4-OH, X= H, F, Cl, CH3, OCH3, OH, NH2, CF3, CN, and NO2) have been calculated by using the (RO)B3LYP procedure with 6-311G(d,p) and 6-311++G(2df,2p) basis sets. The proton affinities of the corresponding phenoxide ions (X-C6H4-O-) have also been computed at the same level of theory. The effect of change of substituent position on the energetics of substituted phenols has been analyzed. The correlations of Hammett's substituent constants with the bond dissociation enthalpies of the O-H bonds of phenols and proton affinities of phenoxide ions have been explored.