Equilibrium function hydrogen-bonded dimers

Hagaman et al. (2012) studied interaction of benzoic acid with metal oxides using solid-state O NMR spectroscopy. Complexes formed by dry benzoic acid with mesoporous silica and nonporous titania and alumina were analyzed. Chemical reactions with silica were not observed, but the behavior of benzoic acid on silica was a function of the water content. The acid was characterized by high mobility as evidenced by a liquid-like, Lorentzian NMR resonance. Excess benzoic acid remained as the crystalline hydrogen-bonded dimer. Benzoic acid reacted with titania and alumina surfaces in equilibrium with air to form the corresponding titanium and aluminum benzoates. In both materials, the oxygen of the O-labeled acid was bound to the metal, showing the bond... 

This appears not to be the case. On average, the crystal field forces have a distortion effect. This was realized from some of the earliest analyses of hydrogen-bond lengths [52]. It arises from two factors one is the influence of many-atom effects, such as cooperativity. The second is the fact that all other atom-pair interactions are striving toward the equilibrium minimum. Since hydrogen-bonded functional groups tend to protrude from molecules, this results in an overall distortion. The most obvious example of this difference is that between the values for the H 0 distances of 1.7 to 1.8 A observed in the ices and 2.0 A for the water dimer (see Thble 4.3). Similarly, the distribution for two-center OwH O bonds in the hydrates of small molecules, discussed in Part IV, has a mean value of 1.80 A, in agreement with the ices. 

More recent results from the theory of hydrogen bonds and proton-transfer processes have been reviewed by Schuster. Ab initio LCAO SCF calculations have been performed on the 1 1 adduct of HCN and HF, in which HCN functions as the proton-acceptor molecule. The predicted equilibrium geometry is linear, FH- NCH, and is well described by the general hybridization model for the hydrogen bond. Del Bene has published the results of ab initio SCF calculations on the series of dimers ROH- -NHg, where R = H, Me, NHg, OH, or F. These dimer structures also fit the general hybridization model. 

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