PROTONATION OF THE CARBONYL GROUP: II. THE BASICITIES OF SUBSTITUTED BENZALDEHYDES

The basicities of seven meta- and para-substituted benzaldehydes have been determined by a spectrophotometric method in sulphuric acid media. The simple Hammett relation does not hold for these bases but a good correlation exists between [Formula: see text] and σ + . The effects of substitution on the wavelengths of maximal ultraviolet absorption in benzaldehyde are compared with those in acetophenone.The basicity of o-tolualdehyde was determined in an attempt to estimate the steric effects of ortho substitution. The effects of symmetrical trisubstitution on the basicity of benzaldehyde and acetophenone are compared and discussed.