Hydrogen bonding, Raman and infrared

The presence in the molecule of two kinds of boron-hydrogen bond is indicated both by its Raman spectrum and by the chemical evidence that four only of the hydrogen atoms are replaceable by methyl groups. Electron diffraction leads to B-H 1.19 A, B-H, 1.33 A, B-B 1.77 A, ZHBH 121.5° and Z.H, BHjj 100°. Raman and infrared spectra of the tetramethyl compound suggest an absence of terminal hydrogen atoms, and electron diffraction shows the four carbon atoms and two boron atoms to be coplanar. 

Further H/D isotopic effects are (i) the increased intensities and decreased halfwidths of D2O (and HDO) bands compared to those of H2O in both the Raman and infrared spectra, and (ii) possible deviations from random distribution of H and D in partially deuterated specimens. From the relative intensities of the two OD (and OH) bands of HDO molecules in hydrates with strongly distorted water molecules (see Sect. 4.2.2) it is assumed that the hydrogen and deuterium atoms are not randomly distributed over the two H positions, but the deuterium atoms rather prefer those positions which are involved in stronger (weaker ) H-bonds. For theoretical studies of the i.r. absorption and Raman scattering intensities of free H2O, HDO, and D2O see Refs. 77,152. 

In summary then, the Raman and infrared spectral studies undertaken after the discovery of the composite nature of native celluloses point to the conclusion that the only difference between the two forms is in the pattern of hydrogen bonding between chains that possess identical conformations. Yet electron diffractometric studies have been interpreted to indicate that the two forms represent two crystalline phases with different crystal habits." More recently, diffractometric studies by Nishiyama have also been interpreted along... 

The structures of a number of stabilized ylides have been studied by l C, iH, and 3ip n.m.r.H and by X-ray crystallography. 12 The X-ray crystal structures of (24) and (27) were compared to those previously determined for (25) and (26) and this data, together with that obtained from Raman and infrared studies on these and related compounds, was used to determine the extent and nature of hydrogen bonding in these systems. 

Intimate information about the nature of the H bond has come from vibrational spectro.scopy (infrared and Raman), proton nmr spectroscopy, and diffraction techniques (X-ray and neutron). In vibrational spectroscopy the presence of a hydrogen bond A-H B is manifest by the following effects ... 

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