X-H stretching bands

In principle, the bands originating from the vibrations of the H20 molecules and NH4+ ions the Raman spectra are weaker than those arising from the vibrations localized in the E043 ions (of these, the strongest band is due to the totally symmetric E04 stretch). This is clearly seen in the case of the Raman spectrum of synthetic arsenstruvite (Fig. 4). On the other hand, the X-H stretching bands are rather prominent in the Raman spectra of struvite itself (Fig. 5). 

Briefly summerizing our present knowledge we can make the following statements. The great breadth of the IR X-H stretching bands is due to combination bands of the... 

The IR spectroscopy, among others, is the most useful. The frequency shift of the X—H stretching band on complex formation (Av) is known as the hydrogen-bond shift. The lower-frequency shift Av of ordinary hydrogen bonds varies from ca. 100-500 cm. but the shifts are... 

Infrared and Raman spectroscopy provide two of the best means of detecting the hydrogen bond. The unbonded X—H stretching band is usually relatively sharp when a compound such as an alcohol is run in a dilute solution in CCI4, for example, or in the vapor state. In more concentrated solutions or in the condensed state, the hydrogen bond X—H Y is formed. Then the hydrogen stretching band shifts to lower wavenumbers and becomes much broader in both the infrared and Raman spectrum. 

A similar effect was observed earlier in [5] for ethene adsorption by X zeolite modified with bivalent cations of Cd and Ca. The C-H stretching bands, which are intense for free ethene, are not detectable at low pressure, while the normally forbidden C-H deformation and C=C stretching bands are the strongest in the spectrum. Further, ethene is weakly adsorbed by monovalent cations such as K, Na or Li and the relative intensities of C-H stretching bands are very strong. 

The X-H stretching vibration is by far the most studied among the vibrations of H-bonded complexes. Its fundamental is distinguished by its high intensity and great breadth compared to the free band. 

Information on the conformational state of the hydrocarbon chains and their orientation has been obtained from external infrared reflection absorption spectroscopy (IRRAS). The first systematic IRRAS studies on phospholipid Langmuir monolayers were reported by Dluhy et al ) (see, for instance fig. 3.62). For DPPC monolayers in the LE phase the positions of the conformation-sensitive symmetric and anti-symmetric C-H stretching bands in the IRRAS spectra were found to be at the same positions as for bilayer systems of DPPC above the Kralft temperature. In the LC phase the frequencies of these bands indicate that the hydrocarbon chains of the lipid molecules are in the all-trans ) conformation (i.e. zig-zag) and analysis of polarized IRRAS spectra show that their average tilt is ca 35° relative to the monolayer normal. This is in reasonable agreement with the tilt angle of 30° obtciined from X-ray diffraction on DPPC monolayers (30°). 

Primary sulfonamides show strong N—H stretching bands at 3390-3330 and 3300-3247 cm 1 in the solid state secondary sulfonamides absorb near 3265 cm x. 

FT i.r, spectroscopy has been used to determine the solvent-induced frequency shifts for the C—H stretching bands of n-octane. Measurement of the FT i.r. spectra for HCl and DCl over the range 2840—8450cm and for HI and DI over the range 3000—10 380 cm" allowed accurate prediction of the TCI and TI spectra. For D2 0, the high resolution (5 x 10 cm ) available using FT i.r. spectroscopy enabled an extended and more precise set of rotational levels to be derived for the vibrational states (000), (020), (100), and (001). Rotational constants and vibrational term values were evaluated for from FT i.r. 

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