LIMITATION OF NMR SPECTROMETRY FOR THE MEASUREMENT OF HYDROGEN BONDING BETWEEN CHLOROFORM AND PYRIDINE
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Publisher:Ohio State University
The measurement of the hydrogen bonding between chloroform and pyridine by NMR spectrometry is complicated by (1) the aromatic ring current effect in pyridine, and (2) the presence of a small extent of the interaction of chloroform at the $\Pi$-site of pyridine. An analysis shows that this ring current effect does not introduce any ambiguity in the evaluation of the thermodynamic parameters. The interaction at the $\Pi$-site of pyridine is shown to introduce ambiguity in the evaluation of the hydrogen bonding parameters for the interaction at the $\Pi$-site, in that an enhanced value of the equilibrium constant and a diminished value of the apparent hydrogen-bond shift is obtained from the experimental data, as well as diminished values of the enthalpy and entropy changes. The hydrogen bonding parameters for the interaction of pyridine with chloroform, 2,4,6-tri-tert-butylphenol and 2,6-di-l-adamantyl-4-tert-butylphenol, as well as the interaction of chloroform with tetrahydrofuran and triethylamine, are obtained and discussed. The results point out the limitation of NMR spectrometry for the measurement of the hydrogen bonding between pyridine and a proton donor.
Author Institution: Department of Chemistry, University of Malaya