Hydroxyl stretching vibration

The exceptional strength of the hydrogen bonding is explained on the basis of the large contribution of the ionic resonance structure. Because of the strong bonding, a free hydroxyl stretching vibration (near 3520 cm-1) is observed only in very dilute solution in nonpolar solvents or in the vapor phase. 

The aluminum oxide surfaces exhibit only a weak Bronsted acidity. Therefore, studies of its surface hydroxyls have usually dealt with their structure. IR spectroscopy appears the most informative and appropriate method for these purposes. The IR spectra cover a wide variety of hydroxyl stretching vibrations, and their assignment is frequently quite a problem. Primarily, it was based on electrostatic concepts and on the electrostatic theory of valency (138). 

Fig. 10.33 Comparison of the infrared spectra of (a) highly crystalline hydroxyapatite (b) poorly crystalline hydroxyapatite and (c) defatted, deproteinated, dried bone showing the regions of the hydroxyl stretching vibration on the right and the hydroxyl libration on the left. Reproduced from [83] with permission from the PCCP Owner Societies.

Figure 2. Hydroxyl stretching vibration spectra of sample 1 (a), 2 (b), 4 (c) and 6 (d) before adsorption of pyridine (1) and after evacuation of pyridine at 4 23K (2) (3) is the difference spectrum between (1)...

The realization that the shape and frequency of the infrared absorption band associated with the fundamental hydroxyl stretching-vibrations in cellulose give considerable information about the hydrogen-bonding conditions in cellulose - led to the development of refined methods for studying the detailed structure of cellulose. 

Binary mbctures of acetic, propionic and butyric acid are converted in the vapor phase over zeolite H-T. From hydroxyl stretching vibration. spectra of zeolite H-T with adsorbed butyric acid, it is concluded that the carboxylic acids have access to the different proton locations in this zeolite. The acids undergo ketonization reactions inside the erionite cavities of the zeolite, and dehydration reactions into anhydrides on the outer surface of the zeolite crystal. The ketonization activity and selectivity is rationalized by transition-state shape-selectivity in erionite cages. Zeolite H-T is particularly suitable for converting an equimolar mixture of propionic and butyric acid into 3-hexanone. 

Fraction 14. This fraction comprised a small portion of the oils and a steady increase was observed in their quantities from HI to VI. They may have presumably polyrac3ric structure. Their infrartjd spectra showed a weak and broad hydroxyl stretching vibration band and very weak C-0 and C-0 absorption bands at 1700 and 1600 wavenumbers respectively. C-H stretching and vibration bands were also observed at very low intensities at 2920 and 1520 wavenumbers respectively. 

Figure 2.44 Hydroxyl stretching vibration range of spectra of ln203/H-beta mixture I after activation in high vacuum at a temperature of 670 K for 1 h (A) and of mixtures I (B) and II (C) after subsequent reduction with H2 at 670 K for 0.5 h. Mixtures I and II contain 0.346 and 0.691 mmol g indium, respectively. The bridging hydroxyl groups at 3610 cm react in a reducing atmosphere, whereas the silanol groups at 3735 cm remain almost unaffected. Reproduced from Ref. (542).

The IR spectra exhibited low frequency shifts of absorption maxima in the range 3600-3100 cm" that correspond to hydroxyl stretching vibrations by 130-140 cm and of absorption maxima of C-0 ether stretching vibrations in the py ranose and fura-nose rings at 1200-1100 cm by 19-20 cm". This may indicate formation of intermo-lecular H-bonds between INAH and the polysaccharides. Furthermore, the absorption band at 1750 cm that is typical of carboityl vibrations in the range 1500-1750 cm weakened. An absorption band of medium strength appeared at 1550 cm and was attributed to vibrations of the pyridine ring of INAH. 

The relative intensity of the band due to the hydroxyl stretching vibration decreases with increase in concentration, with additional broader bands appearing at lower frequencies 3580-3200 cm (2.73-3.13 gm). These bands are the result of the presence of intermolecular bonding, the amount of which... 

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