Nuclear Magnetic Resonance Studies: Part I. The Chemical Shift of the Formyl Proton in Aromatic Aldehydes

Chemical shift data for the formyl proton in some 30 aromatic aldehydes are reported. It was found that meta- and para-substituted benzaldehydes exhibited this peak in the range 9.65–10.20 δ, while ortho-substituted compounds appear at lower field, 10.20–10.50 δ; the former shifts show an approximate correlation with the Hammett sigma parameter. Evidence for steric inhibition of resonance is presented for some ortho-substituted compounds and some interesting solvent effects are discussed.