Conformational studies by dynamic nuclear magnetic resonance spectroscopy. Part 19. Substituent effects upon the rotational barrier of alkylanilines
Abstract
The low-temperature n.m.r. spectra at the 13C frequency (25.16 MHz) showed the non-equivalence of the ortho- and meta-carbons in a number of substituted N-alkylanilines. Line-shape analysis, or measurement at the coalescence temperature, yielded the free energy of activation for the rotational process about the C–N bond. The ΔG‡ values were found to be linearly related to the Hammett constants for a variety of para-substituted derivatives. The barriers were found also to decrease with an increase in the size of the alkyl substituents bonded to the nitrogen atom.
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