Infrared intensities of benzene derivatives as a measure of the substituent resonance effect

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Abstract
Infrared spectra of 39 benzene mono‐derivatives were recorded in the region 1000–1800 cm−1 and the intensities of the bands ν16a and ν16b were determined by computer separation. The intensities correlated with the squared resonance substituent constants σRo as found by Katritzky and co‐workers, but band separation does not represent any essential improvement compared with the earlier simpler technique. With substituents including an NH2 group, there is still an interference with the NH2 scissoring deformation band: in these cases deuteration is more effective than band separation. Several new constants σRo were determined spectroscopically for substituents of interest in pharmacology and these constants were also calculated by a quantum chemical model. The latter procedure seems to be most efficient and reasonably reliable for calculating new σRo constants; the only problem may be with the conformation in the case of axially unsymmetrical substituents. Copyright © 2001 John Wiley & Sons, Ltd.

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