Studies of 13C?H coupling constants: III—the conformational dependence of 1J(13CH) for the formyl proton in aromatic aldehydes

¹J(¹³CH) and ²J(¹³CH) involving the aldehydic proton in ortho-alkylbenzaldehydes have been examined for evidence of a hyperconjugative contribution from the aromatic π-electrons. The expected hyperconjugative effect is obscured by changes in the coupling constants resulting from steric inhibition of resonance.