Substituent effects in IR-(tricarbonylchromium)arenes: II. An IR study of the CO stretching vibrations in alkylsubstituted 7r-(tricarbonylchromium)benzenes

the IR wavenumbers and half-band width's of the carbonyl stretching vibrations of several substituted 7r-(tricarbonylchromium)benzenes in isooctane solution are reported. only small perturbations of C3,.symmetry are observed. the shape of the out-of-phase band is influenced by electronic effects, conformer distribution and solute-solvent interaction. the asymmetry of the E-band in (1'-t-butyl-2',2'-dimetliylpropyl)-7r-(tricarbonylchromium)benzene is ascribe to a direct steric effect. ,me correlation between the CO force constants and electronic substituent parameters is satisfactory for the monosubstituted complexes. the substituent effects are approximately additive for the di- and tri-alkylsubstituted benzene complexes.