Nuclear magnetic resonance study of the hydrogen bonding of chloroform with aliphatic tertiary amines and ethers
- 1 January 1975
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics
- Vol. 71, 622-630
- https://doi.org/10.1039/f29757100622
Abstract
The parameters for the hydrogen bonding of chloroform with 16 aliphatic tertiary amines and 10 aliphatic ethers in cyclohexane medium have been determined by n.m.r. spectrometry. The hydrogen-bond chemical shift ΔAB correlates extremely well with the change in enthalpy ΔH° in each series of the closely related bases. The ethers have a more uniform negative temperature coefficient of ΔAB, than do the tertiary amines. In both the oxygen and the nitrogen bases, the alkyl substituents having the β-methyl group, such as n-propyl and isobutyl, have greater steric hindrance effect in the hydrogen bonding than bulkier substituents having the α-methyl or the γ-methyl group, such as t-butyl or n-butyl, respectively. There is a very good correlation between ΔAB and the sum of the polar substituent constants (Taft σ* values) in the ethers, while in the tertiary amines this correlation is fairly good except for t-butyldimethyl- and cyclohexyldimethyl-amines, in which the ΔAB(and ΔH) values are relatively large. It is suggested that a necessary condition for an uniform temperature coefficient of ΔAB and for a good correlation between ΔAB and Σσ* is that the hydrogen bonds should be formed in the minimum potential energy configuration. Severe steric hindrance causes the hydrogen bonds to be formed in higher energy configurations than the minimum.Keywords
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