Strong amide–halothane hydrogen-bonding observed by nuclear magnetic resonance

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Abstract
The widely-used halothane anaesthetic CF3CHBrCl exhibits a proton magnetic resonance signal in CCl4 solution which is strongly deshielded by addition of N-methylpyrrolidone. This is interpreted as a hydrogen-bonding interaction with halothane C—H as donor and carbonyl as acceptor. From the temperature dependence of the halothane C—H proton chemical shift in the presence of varying concentrations of N-methylpyrrolidone, thermodynamic parameters ΔH0 = −4.7 kcal mol−1 and ΔS0 = −14 cal mol−1deg−1 were obtained. The carbon magnetic resonance spectrum of the two components in CCl4 shows desheilding of the carbonyl carbon at higher concentrations of CF3CHBrCl the halocarbons (1-H) undecafluorobicycloheptane and (1-H,4-H)decafluorobicycloheptane show similar H-bonding behaviour which is comparable with that exhibited by CHCl3.These results are discussed in relation to their possible relevance to the mechanism of action of halocarbon anaesthetics.

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