Strong hydrogen bonds defined

Bonds to Oxygen.—Compounds of Lower Oxidation State. The chemistry of hypophosphorous acid and the metal hypophosphites has been reviewed. Improved dimensions for the HPOaOH" ion have been reported in a neutron-diffraction investigation of the structure of LiH2P03 in particular, the P— distance has been revised to 1.396 A and the presence of strong hydrogen bonds defined. 

Parker37 defined class 4 as solvents "which cannot donate suitable labile hydrogen atoms to form strong hydrogen bonds with an appropriate species and proposed the designation dipolar aprotic solvents he extended their range down to s > 15 and quoted as examples acetone, acetonitrile, benzonitrile, dimethylformamide, dimethyl sulphoxide, nitrobenzene, nitromethane (41.8) and sulfolane (tetramethylene sulphone) (44), where e varies from 21 to 46.5, and the dipole moment p from 2.7 to 4.7 debye. 

It has become clear in the past decade that strong hydrogen bonding has associated with it several characteristic properties. In particular, as hydrogen-bond strength changes, maxima or minima are observed in nmr chemical shifts, the isotope effect on the chemical shift A[5( H) — 8( H)] defined on p. 271, ir Vah/vad band ratios, and in the isotope-fractionation factor, p. 

Proteins are specialized polymers of amides (covered in Chapter 1). Their three-dimensional structures are defined and stabilized by the strong hydrogen bonding found in amides. 

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