Acidity constants of cefetamet, cefotaxime and ceftriaxone; the effect of the substituent at C3 position

The influence of the C3 substituent on the dissociation process of the neighboring ionization group, particularly carboxylic group, was considered. The differences in acidity of CEF, CFX and CFTR (pK1: 2.93, 2.21 and 2.37, respectively) are likely to be caused by the stereoelectronic properties of substituents in the β-position to the carboxylic group due to the combined inductive, hyperconjugative and resonance effects.