Hydrogen bonding is a very significant type of interaction, and is of widespread occurrence. According to Pimentel and McClellan,(1) a hydrogen bond exists between a functional group A—H and an atom or a group of atoms D in the same or a different molecule when there is evidence of bond formation, and when the bond linking A—H and D involves the hydrogen atom already bonded to A. The infrared method, based mainly on intensity measurements of the band assigned to the monomeric species, has been used extensively in the determination of equilibrium constants of hydrogen-bonded systems. It offers the advantages that different hydrogen-bonded complexes can be distinguished, and that relatively low concentrations can be used. For very weak complexes, however, the infrared method has not proved to be a sufficiently sensitive probe of the quantitative aspects of hydrogen bonding. High-resolution nuclear magnetic resonance (NMR) in such cases provides a sensitive measure of interaction, because it permits the measurement of frequencies, which can be done very accurately, rather than intensities, which are more subject to uncertainty. This chapter describes several ways in which NMR is used to obtain equilibrium constants and thermodynamic functions of various hydrogen-bonded systems. In addition, an application of hydrogen-bonding data to the determination of the preferred form of a β-diketone is given.
Nuclear Magnetic Resonance Equilibrium Constant Hydrogen Donor Nuclear Magnetic Resonance Study Nuclear Magnetic Resonance Signal
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