Solvent effects on the infra-red spectra of anilines—VI: Ortho-substituted anilines

Abstract

Measurements of the N-H stretching frequencies are reported for ten ortho-substituted primary aromatic amines dissolved in carbon tetrachloride containing varied mole fractions of hydrogen bond acceptors. Evidence is obtained for the amines assuming non-planar configurations in many of their hydrogen-bonded aggregates. There are Fermi resonance and solvent polarization effects on the νNH values in some instances. The variations in νNH produced by solvent change are not useful in diagnosis of intramolecular hydrogen bonds, but this diagnosis can be made by analysis of the steric and hydrogen-bonding effects which an ortho substituent can produce. When an intramolecular bond is present, νNH asym is raised, and the value of νNH asym—νNH asym) increased, in comparison with the corresponding para-substituted aniline.