THE AMINO PROTON SHIFTS OF SOME SUBSTITUTED ANILINES IN CYCLOHEXANE

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Abstract
The amino proton shifts of 41 ortho, meta, and para substituted anilines at low concentrations in cyclohexane are reported. The shifts for meta and para substituents correlate with Hammett σ constants and it is shown that they are probably proportional to the π-electron density on the nitrogen atom. These shifts also correlate with the pKa values of the corresponding anilinium ions in aqueous acid. The amino proton shifts for the ortho substituents, apart from methyl groups, follow a correlation line which lies about 0.5 p.p.m. to low field from that for the meta and para substituents. This negative deviation is discussed in terms of a weak hydrogen bonding interaction with the ortho substituents and the H—N—H bond angles as derived from infrared data.