Overtone hydroxyl

The vibrational overtones and combinations of hydroxyl groups and thek associated molecular water occurring in the spectra of various gel siUca materials are summarized in Table 2 and discussed in References 3, 5, and 22. These peaks and bands found in the preparation of alkoxide-derived siUca gel monoliths are identical to those described for siUca gel powders (41). 

Figure 8.9 Diffuse reflectance infrared spectrum of a silica support, showing silica vibrations at frequencies below 1300 cm1, overtones and combination bands between 1700 and 2050 cm-1, and various hydroxyl groups at frequencies above 3000 cm 1. The sharp peak at 3740 cm"1 is due to isolated OH groups, the band around 3550 cm 1 to paired, H-bonded OH groups, and the band around 3660 cm 1 to hydroxyls inside the silica (courtesy of R.M. van Hardeveld, Eindhoven).

I. The changes of the overtone 0—H hand of the surface hydroxyl groups on adsorption and immersion... 

Figure 14a shows the IR spectrum of a dried silica disc. The sharp band at 3755 cm 1 is consistent with the isolated hydroxyl groups (Type A sites) present, and the broad bands at —1980 and 1860 cm 1 are overtones of the Si-O vibrations. Treatment of the disc with h toluene solu-... 

Compound 1 This spectrum is most useful for what it does not show. There is a carbonyl absorption at 1714 cm-1 and little else. There is no aldehyde C—H, no hydroxyl O—H, and no N—H. The weak absorption at 3400 cm-1 is probably an overtone of the strong C=0 absorption. The carbonyl absorption could indicate an aldehyde, ketone, or acid, except that the lack of aldehyde C—H stretch eliminates an aldehyde, and the lack of O — H stretch eliminates an acid. There is no visible C=C stretch and no unsaturated C—H absorption above 3000 cm-1, so the compound appears to be otherwise saturated. The compound is probably a simple ketone. 

As mentioned above, HOSi(OA)3 may be taken as the simplest cluster model of the terminal hydroxyl group in silicas. Indeed, even with this cluster CNDO/BW provided a quite satisfactory description of the lower part of the curve representing potential energy as a function of the OH stretching vibration coordinate ROH (Fig. 2) (48,49). The respective experimental curve was plotted by Kazansky et al. (49) based on the analysis of the fundamental frequency vOH and the first overtone of the characteristic OH stretching vibration in terms of the Morse potential function. The frequencies of the second and third overtones were also determined in that work, and it was shown that the Morse potential reproduced well the potential curve within a rather wide range of ROH. 

The middle IR could be used to look at the C-0 ester and ether bands and the secondary hydroxyl in the 1000 to 1500 cm"l region. However, more useful were the results from the near IR in which the epoxy C-H, C=0, and 0-H bands can be compared to the first overtone of the 3.5. M c-H band which appears at 1.66... 

The Overend s [9] Fermi resonance (FR) theory was adopted according to Odinokov [10] in the calculation of the bridging hydroxyl frequencies of stretching vibration v(OH) and overtones of inplane 25(OH) and out-of-plane 2y(OH) vibrations unperturbed by Fermi resonance from the experimental spectrum. It is considered that the separation of unperturbed AE° = - E% and... 

Fig. 10.34 shows the INS spectrum of ox femur as the organic component is progressively removed [83]. Fig. 10.34a is very similar to that of the protein Staphylococcal nuclease. Fig 10.32, and emphasises one of the problems of working in this field because proteins are largely made of the same monomers (amino acids), the INS spectra of very different proteins tend to look very similar. Removal of the fat results in little change in the spectrum, Fig. 10.34b. It can be seen that elimination of the protein is highly effective, Fig. 10.34c the C-H stretching modes just below 3000 cm" and the C-H deformation modes at 1200-1500 cm have both disappeared. There is a weak, broad peak at 630 cm and its overtone near 1300 cm. For comparison, the INS spectrum of a highly crystalline reference hydroxyapatite is shown in Fig. 10.34d. The frequency match of the of the residual bone peak and that of the hydroxyapatite is exact, the width of the peak is attributed to heterogeneous broadening. The spectrum demonstrates that hydroxyl groups are still present in bone.

Similarly, the low frequency overtone at 6950 cm-1 associated with acidic OH vanishes, while the silanol overtone band develops at 7325 cm-1 (9) and the ( v + 6) combination shifts to 4540 cm-1. These observations are consistent with the creation of silicon defects in the structure of dealuminated Y zeolites (10) while the weak overtone band at 7240 cm 1 is probably related to hydroxylated aluminium species extracted from the lattice (11, 12). Thus, the near-IR spectra give evidence for the decrease of the number of Bronsted acid sites as a result of dealumination. 

Reflectance spectroscopy brings evidence for a parallel decrease in hydroxyl number. Such a conclusion agrees well with the results of IR absorption the bands at 6950 and 7140 cm-1 are overtones of the fundamental bands at 3560 and 3630 cm 1. The latter is associated with the more acidic OH groups (18). These bands progressively weaken as dealumination increases. In highly dealuminated materials, the band at 7325 cm-1 is the overtone of the silanol absorption at 3740 cm-, but contrary to the fundamental (18) no splitting of the overtone was observed. 

The introduction of hydrophilic groups, such as hydroxyl, amino, or carbonyl, into the barbiturate side-chains results in complete loss of hypnotic activity. Many such derivatives have been made in recent years, with the object of producing other types of pharmacological action. Examples of such compounds are provided in the sections which follow. It was recognised at an early date that the hypnotic activity of the barbiturates was related to their lipophilicity. In 1899 Meyer and Overton [159] had proposed that all chemically indiiferent bodies which are soluble in lipids act as narcotics to living protoplasm. It was then assumed that relative activities of various narcotics depend on their distribution between body fats and fluids. 

Moisture and hydroxyl number are important parameters, which are determined by measuring either the first overtone at 6890 cm or the combination band at 5180 cm . A few details about chemical structure are accessible by interpretation of these bands. Changes in hydrogen bonding lead to changes in the band shape and band location. Difference spectra or second derivatives must be calculated in order to detect minor chemical interactions of OH with other molecular species in the sample. The number of double bonds is another important parameter to describe the properties of fats and oils, e. g. their degree of unsaturation. 

The OH and OD stretching modes of free OH radicals are at 3568.0 and 2632.1 cm respectively (645), which corresponds to an isotopic shift factor of 1.3556. This value is again lower than the theoretical one and is similar to the values reported in Table 2.24 for isolated surface hydroxyls. These measured frequencies of the stretching modes are known to be affected by anharmonicity. The harmonic OH and OD frequencies (calculated on the basis of overtone modes) are at 3735.2 and 2720.9 cm, respectively. Thus, the isotopic shift factor for the harmonic frequencies is 1.3728, which is very close to the theoretical value of 1.3736. The same value for the hydroxyl anion, OH, is 1.3726. Therefore, one can conclude that the deviations of the isotopic shift of free OH radicals and ions are mainly the result of anharmonicity. Similar calculations for isolated surface OH groups (21) show that also in this case, the deviations are mainly caused by anharmonicity (isotopic shift factor of the harmonic frequencies of 1.372-1.373). 

---