Ammonia-water complex, hydrogen bonding

Two additional systems in which hydrogen bonds are expected to play a dominant role, ammonia-water complex and 2-aminoethanol, were calculated ab initio and by the new MM3 force field. Two ammonia-water complexes were considered, one with an N... H—O bridge (32) and the other with an O... H—N bridge (33). As expected from the relative H-donor/H-acceptor properties of nitrogen and oxygen, 32 was calculated... 

TABLE 15. Energetic and structural parameters for two ammonia-water complexes (32 and 33) as calculated ab initio (6-31G + BSSE correction) and by the MM3 force field augmented with a directional hydrogen bonding potential function0. Reproduced by permission of John Wiley Sons Ltd from Ref. 30b... 

In addition to hydrogen halides, water is the most studied HBD in the gas phase. The structures of the complexes with water, dinitrogen, carbon monoxide, ozone, benzene, ethane, formaldehyde, formamide, 1,4-dioxane, ethylene oxide, tetrahydropyran, difluo-romethane, pyrazine, pyrimidine, pyridazine, benzonitrile, quinuclidine, ammonia, methy-lamine, trimethylamine and so on can be found in the Mogadoc database [29]. In the water-morpholine complex [30], water is hydrogen bonded to the nitrogen and not to the oxygen, as predicted by the higher HB basicity of amines than that of ethers. 

Ammonia is very soluble in water because the NH3 molecules can form hydrogen bonds to H20 molecules. Ammonia is a weak Bronsted base in water it is also a reasonably strong Lewis base, particularly toward d-block elements. For example, it reacts with Cu2+(aq) ions to give a deep-blue complex (Fig. 15.4) ... 

For attack of F on acrylic acid, first a hydrogen bonded complex is formed which then proceeds to the transition state and then to a stable carbanion. The methyl in the methacrylic acid reduces stabilization of the carbanion as predicted. Subsequent studies using ammonia as the nucleophile indicated that attack proceeded by a rate-determining intramolecular proton transfer from the nucleophile to the ligand, assisted by a discrete water molecule that acts as a catalyst17. They predicted that acrolein underwent 1,4-addition, acrylic acid either 1,2- or 1,4-addition and acrylonitrile 1,2-addition. 

Fig. 12.1 The water-ammonia complex connected through O-H—N hydrogen bonding...

Hunter, K. C. Rutledge, L. R. Wetmore, S. D. The hydrogen bonding properties of cytosine A computational study of cytosine complexed with hydrogen fluoride, water, and ammonia, J. Phys. Ghent A 2005,109, 9554-9562. 

Yeo, G. A. and Ford, T. A.,Ab initio molecular orbital calculations of the infrared spectra of hydrogen bonded complexes of water, ammonia, and hydroxylamine. Part 6. The infrared spectrum of the water-ammonia complex. Can. J. Chem. 69,632-637 (1991). 

In both water and ammonia complexes, the clusters formed by interaction with the ANI molecule become invariably stronger following ionization. Thus, the hydrogen bond pattern involving amine could be modified by controlling its charge. 

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