Abstract The conformational equilibrium ap⇌ sp of the title compounds was investigated by two methods: dipole moment measurement in benzene solution and IR spectroscopy of the carbonyl band in decahydronaphthalene solution. Approximately 71% of the ap rotamers were found for 2-cyanobenzoates (II, III), and between 60 to 80% for (Z)-3- cyanopropenoates (V, VI). This result does not reveal any special attractive interaction ...