Wittig Synthesis and13C‐N.M.R. Investigation of Pyridineanalogous ChalconesWittig type reaction of the three isomeric pyridinealdehydes with benzoylmethyl‐enetriphenylphosphorane yields azachalcones1a–cwhich have the E‐configuration. The complete13C‐n.m.r. analysis of these compounds is reported. From the chemical shifts of the Cα‐signals and on the basis of a Hammett relationship σ‐values of the three isomeric pyridine groups are calculated and compared