Effects of α Substitution on the Carbonyl Stretching Frequencies of Phenyl Carboxylates

Article abstract of DOI:10.1021/jo00347a039

The infrared carbonyl stretching frequencies for several esters of the general formula R¹R²R³C-COOPh were determined in carbon tetrachloride.The ?^* and E_s Taft parameters as well as the ν_Charton parameters for the same esters were determined.The carbonyl stretching frequencies are well correlated by a dual substituent parameter treatment: ν_C=O = ν_C=O⁰ + ρ^*?^* + δE_S or ν_C=O = ν_C=O⁰ + ρ^*?^* + Ψν_Charton.In both cases the steric parameter is much larger than the polar parameter, suggesting that the effect of the substituents on the carbonyl stretching frequencies is of a steric nature, although a small contribution of the polar effect is observed.