Raman intensity and conjugation. IV‐determination of the conjugation between a phenyl ring and a carbonyl group by Raman intensity

The Raman intensities SCO and S8a,b of the CO‐stretching vibration and the 8a, b‐ring vibrations of some compounds of type C6H5‐CO‐X (X = NHNH2, NH2, OC2H5, OCH3, CH3, CH2Cl, H, CL, CF3, CN) have been measured using the excitation lines of an argon ion and a krypton ion laser. The intensities in the two series are linearly related and the (RI)1/2 values correlate both with Hammett substituent parameters and with the extinction coefficients of the longest wavelength u.v. absorption band. The results are interpreted by showing that the intensities here are almost independent of the resonance Raman effect and thus reflect the conjugation effect. Relative Raman intensity values can thus be used to measure the conjugation between a phenyl ring and various carbonyl groups.