Structure of Hydrogen-Bonded Complexes

Hydrogen-bonded complexes are common throughout chemistry. They generally involve a hydrogen attached to a heteroatom (usually nitrogen or oxygen) interacting with another heteroatom. 

Y ater dimer distance variation provides a sequence of structures for water dimer at different nonbonded OH distances. Plot energy (vertical axis) vs. nonbonded OH distance (horizontal axis). What is the optimum distance How much energy is required to increase this distance by 10% How much is required to reduce the distance by 10% Are the two distortion energies about the same magnitude If not, explain why not. 

One after the other, examine methanol dimer and acetic acid dimer. Do the hydrogen-bond lengths in these systems differ significantly from the optimum distance in water dimer Are the hydrogen-bond angles in these compounds significantly different from those in water dimer Rationalize your results. 

Electrostatic potential map for hydronium+3 water molecules shows most positively-charged regions (in blue) and less positively-charged regions (in red). 

In the gas phase, the structures of a large number of hydrogen halide complexes X—H B have been investigated by rotational spectroscopy [28]. A number of rules have been derived from these structures  

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. 

Another empirical equation has been established to predict the strength of hydrogen bonds between small amphoteric molecules such as H2O, HF, HCl, HBr, HC=N, HCMIIH and NH3 [37], from the intermolecular stretching force constants. This equation can be used to quantify the spectroscopic observation that water is the HBA in its complexes with HCl, HBr, HON and HCM h and is the HBD with NH3. 

Correlations between HB iength, inversely related to HB strength, and chemical descriptors of elements E, such as electronegativity, are clear-cut only within a period because. 

Many other relationships between geometric parameters of the HB and basicity can be found in a book [47] and a review [48] on the hydrogen bond in the solid state. 

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Carroll, M.T., Chang, C. and Bader, R.F.W. (1988) Prediction ofthe structures of hydrogen-bonded complexes using the Laplacian of the charge density, Mol. Phys., 63, 387 105. 

Figure 2. Structure of hydrogen-bonded complexes between an aliphatic alcohol and HDBP and H2MBP...

M. T. Carroll, C. Chang, and R. F. W. Bader, Mol. Phys., 63, 387 (1988). Prediction of the Structures of Hydrogen-Bonded Complexes Using the Laplacian of the Charge Density. 

Hoogsteen K (1963) The crystal and molecular structure of hydrogen-bonded complex between 1-methylthimine and 9-methyladenine. Acta Crystal-logr 16 907-916. 

Figure 3. X-Ray structure of hydrogen bonded complex [(PMe3)2(NO)(CO)ReH2 indole].

Fig. 6. Structures of hydrogen-bonded complexes and covalently bonded aromatic esters...

Recently, new interesting results were reported (by electrom c publishing) about the structures of hydrogen-bond complexes formed between silanols and amines or... 

Austerheun, A. andGramstad, T. (1985) Studies of hydrogen bonding. Part XXXII. The structure of hydrogen-bonded complexes betweenp-fluorophenol and various nitriles. Acta Chem. Scand., B39, 583-587. 

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