Stretching absorption bands

The IR spectra of NDCM salts exhibit cyanide stretching absorption bands in the 2250-2210 cm region and three broad absorption bands associated with the coupling of the v(NO) and v(CC) modes in the 1375-1210 cm region (Table 8). The electronic spectra of the NDCM salts exhibit characteristic jt jt and n n electronic transitions at ca 300 and 480 nm, respectively. In aqueous solution the UV-vis spectra of, e.g., the lithium and barium salts exhibit an additional absorption at 401 nm, which can be attributed to the solvatochromic effect of water. 

Acid halides. Acid halides show a strong C=0 stretching absorption band at the high frequency end of the carbonyl stretching region. This may be explained by considering the electronic structure of an acid chloride. 

Yellow 4-hydroxy-2//-l -benzothiopyran-2-thioncs result from the reaction of 2 -chloroacetophenones with CS2 in the presence of NaH. Their IR spectrum shows no carbonyl stretching absorption band. However, treatment of a solution of the thione with concentrated acid results in the precipitation of the pale yellow 2-mercaptothiochromone 271 for which vc=o occurs at 1610-1620 cm-1. Treatment with base and then dilute acid regenerates the thiocou-marin. Both tautomers appear to exist independently of each other (Equation 20) <1987AJC1179>. 

Investigation of methanol-pyridine complexes, on the other hand, produced a relatively narrow (75 cm 1 FWHM) bleached hole that is burned into the 260 cm 1 FWHM OH-stretch (v = 0 -> 1) absorption band. The methanofpyridinc complex OH-stretch absorption band was better fit by a Gaussian function than with a Lorentzian bandshape, indicating this system is inhomogeneously broadened on the >1 ps timescale. 

Fig. 6-9. The vc o stretching absorption band in the infrared spectrum of camphor (a) in the gas phase, (b) in n-heptane, (c) in tetrachloromethane, (d) in pyridine, (e) in methanol, and (f) in l,l,l,3,3,3-hexafluoro-2-propanol [378].

Figure 3 OH-stretching absorption bands and their component bands of silanol in various heat-treatment temperatures, a, b, c, d, e, and f show the maximum wavenumbers of the component bands at 3870, 3750, 3630, 3470, 3260, and 3030 cm-1, respectively (Reproduced by permission from Bull. Chem. Soc. Japan, 1974, 47, 553)...

The strength of a C — H bond depends on the hybridization of the carbon The greater the s character of the carbon, the stronger the bond it forms (Section 1.14). Therefore, a C—H bond is stronger when the carbon is sp hybridized than when it is hybridized, which in turn is stronger than when the carbon is hybridized. More energy is needed to stretch a stronger bond, and this is reflected in the C—H stretch absorption bands, which occur at 3300 cm if the carbon is sp hybridized, at 3100 cm if the carbon is sp hybridized, and at -2900 cm if the carbon is sp hybridized (Table 13.5). 

Figure 4. Optical image and two infrared images of a dividing cell (35 pm x 20 pm) obtained from IR spectromicroscopy. These chemical maps are derived from the strength of absorption bands from approximately 100 infrared transmittance spectra collected over the area of the dividing cell. The maximum in the color scale (yellow) represents the position of the maximum absorption by the cell, while the minimum (blue) represents no absorption by the cell. Strikingly, the intensity map of the amide II absorption band shows two peaks in the center of the two halves of the cell, representing the position of two separate nuclei before the cell division is complete. The intensity map of the C-H stretch absorption bands shows that lipids are concentrated at the contractil ring, where the cleavage furrow is located. [Used by permission of the National Academy of Sciences, U.S.A., from Jamin et al. (1998), Proc Natl Acad Sci, Vol. 95, Fig. 3, p. 4839.]...

The situation is more complicated for the B-DNA helix (see Fig. 4). Because of the stronger overlap between the guanine and cytosine CO-stretch absorption bands, it is more difficult to directly probe a spectral relaxation as observed for the Z-DNA helix. 

CHBrs. The C X stretch absorption bands occur in the hngerprint and aromatic regions and are quite strong (Table 4.14). Several halogen atoms on the same C atom cause an increase in absorption intensity, more absorption peaks and a shift to higher wavenumbers (higher frequency or shorter wavelength) for the C—X stretch. 

Cole and Macritchie (1959) have used intensity measurements of the hydroxyl stretching absorption band at various temperatures to determine the energy of the hydrogen bond formed between a substituted cyclohexanol, frans-dihydrocryptol (XI), and a cyclic ether, dioxane (XII) in tetrachloroethylene solutions. The methods... 

Figure 5.2. Result of deconvolution into Gaussian profiles of stretching absorption band of Si02 films 27 nm (a, b) and 600 nm (c, d) thick. Band was recorded at > = 0° (a,c) and in p-polarized light aX(p = 75° p, d).

Fig. 5.20 [169]. One can see that with a decrease in X, the spectrum evolves from that of a-Si H to that of a-Sii-xQ.K as the SiC stretching band shifts from 760 to 800 cm" and becomes more asymmetric in the higher frequency region and the Si-H stretching absorption peak shifts from 2000 cm (as in pure a-Si H) to 2090 cm (as in an a-SiC H alloy). The gradual shift of the Si-H stretching absorption band may be a result of the induction effect as the number of (more electronegative) carbon atoms attached to Si—H increases [149]. Variations in the IR absorption spectra are accompanied by the growth of the optical band gap from 1.7 eV (pure a-Si H) to 2.6 eV (a-Sii cCx H alloy with X = 0.17) [169]. The carbon content in the film can be calculated from the SiC stretching absorption band at 760 cm by using Eqs. (5.13) and (5.14) and the coefficient Ai = 2.1 X lOi cm-2 [171].

Carbonyl groups of aldehydes and ketones give rise to very strong C = 0 stretching absorption bands in the l665-1780-cm region. 

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