Substituent and coupling effects in the IR spectra of arylidenecyclanones

By studying the IR spectra of arylidenecyclanones possessing exocyclic CC double bonds, a correlation has been found between the wave number and intensity values of the ν CO and ν CC vibrations and the substituent constants. Transmissive factors of the CC double bond have been calculated and these indicated that the most pronounced conjugation occurs in the case of the indanones and the smallest for 1-thiochromanones. It has also been established that the substituent effect transmitted by the CC double bond is mainly of a resonant character. Coupling of the ν CO and ν CC vibrations has been studied by the method of Taylor and Smith. It has been concluded that in the case of arylidene-indanones possessing strong coupling, of the two intense bands between 1600 and 1800 cm^?1 the one found at higher wave number is a result of an out-of-phase (ν_as) coupling of the ν CO and ν CC vibrations while the other originates from an in-phase (ν_s) coupling. Coupling was less in the case of the other compounds investigated. Our studies prove that for the evaluation of the substituent effects the coupling phenomena should be taken into consideration.