NH vibrations

NH vibrations. Fuson et al. [18] have analysed the results of Randall et al. [17] in addition to their own and have shown that in soUd compounds the NH stretching vibration falls in the range 3390—3260 cm . This covers fifteen a-amido-acids studied by Randall et al. and a further ten samples examined by themselves. On formation of esters in which the hydrogen bonding possibilities are reduced, this frequency increases, and is then closer to the normal range. Micheel and Schleppinghoff [16] also find values of 3350 cm in a series of A -acetyl amino-acids. 

The region 3000—2000 cm . Like the amino-acids, the amido-acids show in many cases broad and rather weak absorption bands in this region. An analysis by Fuson et al. [18] of the 

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These methods are now obsolete in comparison with spectroscopic methods. Werbel has shown that the structures of these isomers are easily determined by NMR (125) (see also Table VI-5). Furthermore. 2-imino-4-thiazoline derivatives are characterized by their stretching C=N vibration at 1580 cm , absent in their 2-aminothiazole isomers, and by the stretching NH vibration that appears in the range of 3250 to 3310 cm for the former and between 3250 to 3340 cm" for the latter (131). Ultraviolet spectroscopy also differentiates these isomers (200). They can be separated by boiling in ethanol the thiazoline isomer is usually far less soluble in this solvent (131),... 

The infrared (IR) spectra of 1,10-phenanthroline, its hydrate and perchlorate in the region 600-2000 cm-1 have been obtained, and the principal features of the spectra interpreted.66 Further studies on the IR spectra of 1,10-phenanthroline,67-69 substituted 1,10-phenanthrolines,70,71 and 1,7-phenanthroline67 have also been reported. The IR spectrum of 4,7-phenanthroline in the region 650-900 cm-1 has been analyzed, and the C—H out-of-plane deformation frequencies were compared with those of phenanthrene and benzo[/]quinoline.72 The IR spectra of salts of 1,10-phenanthroline have been taken, and the NH vibrations determined.28,73 Infrared spectroscopy has been used to detect water associated with 1,10-phenanthroline and some of its derivatives on extraction into nitromethane from aqueous solution.74 The Raman spectrum of 1,10-phenanthroline has been compared with its IR spectrum.75 Recently, the Raman and IR spectra of all ten isomeric phenanthrolines were measured in solution and solid states, and the spectra were fully discussed.76... 

A comparison of the relative frequency shifts of the NH- and ND stretching vibrations of pyrrole and pyrrole-l-d in both polar and nonpolar solvents indicates that the stabilities of both ND-w and ND-X bonded complexes are less than for the corresponding NH complexes.131,131a 143 The isotope effect results from a difference in energies of the fundamental states of the ND and NH vibrators which is reflected in the energy differences of the double potential minimum of the hydrogen bond.143... 

Considerable interest has also been shown in the NH vibrational modes, particularly in connection with hydrogen bonding and molecular association. The frequency and integrated intensity of the NH stretching vibration in nonpolar solvents relative to that observed in the vapor phase is consistent with the Kirkwood-Bauer-Magat relationship,105, 347 but where a strong interaction exists between the solvent and the pyrrole molecule a large deviation from the expected value occurs (see Section II, B). 

O-protonation of 5,5-dimethyI-3-(N-pyrrolidyl)-2-cyclohexene-l-one [246], based on the infrared spectrum of its perchlorate (Leonard and Adamcik, 1959), was confirmed by ultraviolet spectra (Alt and Speziale, 1965). The protonation of the bicyclic system [247], which is certainly N-protonated owing to steric hindrance to meso-merism, leads to a cation with a maximum absorption at 212 nm (in ethanolic hydrochloric acid) and three strong infrared absorptions in the solid hydrochloride at 1655 cm-1 and 1720 cm 1 for the double bonds and at 2430 cm 1 for the NH-vibrations (Dolby et al., 1971). 

The infrared spectrum of a protein is dominated by its peptide backbone amide I (C=0) and amide II (C-N. NH) vibrations. Fig. 6.6-1 shows a typical IR absorption spectrum of a hydrated protein film, in this case bacteriorhodopsin. In addition to the strong amide I (1658 cm ) and amide II (1546 cm ) bands water also contributes largely to the absorption (3379 cm , 1650 cm ). 

Figure 42. NHu = 0 and 1 LIF signal intensities versus HI photolysis wavelength under bulk conditions. The thresholds differ by roughly an NH vibrational quantum. Note the qualitative difference with the data presented in Figure 40.

Strong hydrogen bonds in 1 should result in the NH vibrations being shifted to low frequencies. Actually, the NH stretching vibration has not yet been identified in the IR spectrum of 1, even though the calculations predict that it should correspond to the most intense band [41, 42]. The IR and Raman experiments could... 

The decay of C-H stretching (and OH and NH) vibrations in liquids has been studied by IR-Raman spectroscopy... 

The thermal vibrations of atoms in molecules lead to absorption bands in the infrared (IR) region (Bellamy, 1964 Colthup et al., 1964 Hesse et al., 1984). IR bands are most intense if a dipole is induced by the vibration (OH, NH, CH, C=0, C=N). The mass of the interacting atoms Ml and M2 and the bond strengths defined by a force constant f determine the wave number n or energy of an infrared absorption band v = K(f/M ) , where the reduced mass is M = MjM2/Mj+M2 and K is a constant conversion factor. The frequency n for the CH-stretch vibration is around 2900 cm for C=0 close to 1700 cm. Hydrogen bonds lead to a broadening and low-frequency shift of OH and NH vibrations (3400 cm —> 3200 cm ). 

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