Hydrogen Bonding in Organic Compounds. VI. Interaction between Groups in ortho-Substituted Anilines

Abstract

The infrared spectra of anilines, with a single methyl group as ortho-substituent, conform to the modified Bellamy and Williams equation which was found to correlate the antisymmetric and symmetric stretching frequencies of the NH₂ group when only meta- or para-substituents were present. Methyl substituents at both positions 2 and 6 to the amine produce a change that can be described as anti-hydrogen bonding. Substitution by alkoxy groups or halogen at the position ortho to the amine group causes deviations from the equation in the direction indicative of hydrogen bonding. Monodeuterated 2-bromo-, 2-iodo, and 2-cyanoaniline give evidence of extremely weak hydrogen bonds by a small difference in the NH and ND vibrations of two isomeric forms bonded through H and D respectively. The spectra of monodeuterated 2-alkoxy-, 2-fluoro-, and 2-phenylaniline did not show any resolution of the bands due to NH and ND vibrations, and hydrogen bonding between the ortho-substituents can be regarded as negligible in these compounds. An o-trifluoromethyl substituent appears to exert a repulsive effect on the amine group with no formation of a hydrogen bond. Rotational isomers occur in carbon tetrachloride solutions of 2,6-dihalogeno-4-nitroanilines.