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

Infrared spectra of 39 benzene mono-derivatives were recorded in the region 1000-1800 cm(-1) and the intensities of the bands v(16a) and v(16b) were d etermined by computer separation. The intensities correlated with the squar ed resonance substituent constants sigma (R)degrees as found by Katritzky a nd co-workers, but band separation does not represent any essential improve ment compared with the earlier simpler technique. With substituents includi ng an NH2 group, there is still an interference with the NH2 scissoring def ormation band: in these cases deuteration is more effective than band separ ation. Several new constants sigma (R)degrees were determined spectroscopic ally for substituents of interest in pharmacology and these constants were also calculated by a quantum chen-deal model. The latter procedure seems to be most efficient and reasonably reliable for calculating new sigma (R)deg rees constants; the only problem may be with the conformation in the case o f axially unsymmetrical substituents. Copyright (C) 2001 John Wiley & Sons, Ltd.