Hydrogen bonding Unusually strong

Hydrogen bonding unusually strong dipole-dipole attractions that occur among molecules in which hydrogen is bonded to a highly electronegative atom. 

Perrin CL (2010) Are short, low-barrier hydrogen bonds unusually strong Acc Chem Res 43 1550-1557... 

Moderate errors in the total pressure calculations occur for the systems chloroform-ethanol-n-heptane and chloroform-acetone-methanol. Here strong hydrogen bonding between chloroform and alcohol creates unusual deviations from ideality for both alcohol-chloroform systems, the activity coefficients show... 

The unusually high boiling points of HF, H20, and NH3 result from an unusually strong type of dipole force called a hydrogen bond. The hydrogen bond is a force exerted between an H atom bonded to an F, O, or N atom in one molecule and an unshared pair on the F, O, or N atom of a neighboring molecule ... 

Note that the m(dstrong electrolytes in dilute solution. It results because the charged ions break up the hydrogen bonded structure of the water and decrease the heat capacity of the solution over that of pure water. Thus, the contribution of Cp. 2 to Cp m is negative. 

What makes FHF an attractive species to investigate by nmr spectroscopy is that it consists of three nuceli each with spin 1/2 bonded directly. Also, the proton of the strong hydrogen bond should have an unusual chemical shift. Early work failed to detect the expected F doublet and H triplets (e.g. Soriano et al., 1969), and it was not until the importance of the solvent was appreciated that coupling was observed (Fujiwara and Martin, 1971, 1974a,b). Suitable media were found to be the dipolar aprotic solvents acetonitrile, nitromethane and dimethylformamide. 

Binding to lysozyme stabilizes a conformation in site D compatible with the alternative mechanism. (i) Hg of residue D does not interact with residue E but forms a strong hydrogen bond to the mainchain 0 of residue 57, a residue involved with the unusual buried p turn in lysozyme. (ii) The value of 0 between D and E, which was -54 in the initial structure, stabilized at -62 , near the optimum of -60 for stereoelectronic assistance. 

---