CH stretching region

Figure 24. Nonresonance Raman spectra of the CH stretching region of DOPC-Ba in S(PS)n-Bafflm[23]. 

Fig. 9.28 Analysis of the CH-stretching region (3000-2800 cm ) and the amide I band around 1650 cm V (a) ER-FTIR spectrum of poly(2-ethyl-2-oxazoline) (PEOx) as grown on the triflate functionalized HUT SAM. (b) ER-FTIR spectrum of HUT SAM. (c) Subtraction result of (a)-(b). (d) Bulk spectrum of PEOx. In the spectrum to the left, a significant shift...

This model has proven adequate for the description of VCD in the CH stretching region of a number of molecules. 

The VCD spectra of molecules of the form CH3C HR,R2 have been investigated in the CH stretching region (20, 57-59) and the 16(X)-900-cm mid-infrared region (59, 60). The ROA of this type of molecule has also been recorded (II-14). In particular, a-deuterated ethanol and a-phenylethane derivatives have been studied. 

Figure 3. VCD and absorption spectra in the CH stretching region (a) a-phenylethanol, 0.074 M in ecu, path length O.IO cm, (b) (+)-a-phenylethyl isocyanate, 0.087 M in CCU, sample path length 0. IS cm. The time constant was 10 s, and the resolution was 6 cm. (Reproduced with the permission of North Holland Publishing Co., from ref. S9.)...

The mid-infrared region is considerably more difficult to interpret than the CH stretching region. This fact again points to the fact that chromophores responsible for VCD are delocalized over the chiral frame. 

Figure 4. VCD and absorption spectra in the CH stretching region of (+)-dimethyl- rans-l,2-cyclopropanedicartx)xylate-dg, O.OSO M in CCI4. Sample path length 0.3S cm, time constant 10 s. (Reproduced with peimission from ref. 62. Copyright 1981 American Chemical Society.)...

Figure 5. VCD (lower traces) and transmission spectra (upper trace) in the CH stretching region of (-)-menthone (----), 0.059 M in CCI4, and (+)-isomenthone (--), 0.062 M in CC ,. (Repro-...

L-Alanine, the simplest chiral amino acid, has been the subject of the most extensive study and serves as the prototype for the other amino acids. A complete vibrational assigrunent has been obtained (85, 86) based on solution phase IR and Raman spectra and solid phase Raman spectra for alanine-do, alanine-C -di, alanine-C(3-d3, and alanine-C -d-C -d3. In the CH stretching region, the antisymmetric methyl stretches are assigned at 3006 and 2989 cm , the methine stretch at 2970 cm , and the Fermi resonance diad involving the symmetric methyl stretch and the overtone of the antisymmetric methyl deformation at 2950 and 2893 cm. The calculated frequency for the unperturbed symmetric methyl stretch is 2930 cm . 

In addition to the VCD from the methine C H stretching vibration, which alone gives rise to a strong positive bias in the CH stretching region, the CH stretching VCD of amino acids contains contributions from two other sources. Minor features can be attributed to combination bands of the very intense antisymmetric carboxylate stretch at 1610 cm with the symmetric carboxylate... 

Figure IS. VCD and absorbance spectra in the CH stretching region of deuterated L-alanine...

Studies of amino acid VCD outside the CH-stretching region has been limited. For L-alanine, the VCD in the 1600-1200-cm region is characterized by a bisignate couplet at 1337 cm (—) and 1291 cm (-(-) corresponding to the two perpendicular methine bending modes (92, 93). 

Figure 20. VCD and absoibance spectra in the NH and CH stretching regions of rrij(ethyl-...

Figure 4. Raman spectra of methylated silica in the CH stretching region using 1.7 W of laser power at 488.0 nm. The scan rate and response time constant (seconds) were as follows (A) 500 cm"V min, 0.1 s (B) 50 cm 1 /min, 1 s (C) 10 cm 1 /min, 10 s. Curve D shows the IR spectrum recorded with a scan time of 83 cm 1/min and a time constant of Is. The vertical bar represents 3000 Hz for the Raman spectra and a transmittance of 0.20 for the IR spectrum (21).

Fig. 22a and b. Infrared spectrum obtained from a cluster of Huronispora (Gunflint chert) in demineralized condition (compare Figs. 6a-c) b) High sensitivy recording of CH stretching region. Field of measurement 25 pm diam. (Pflug, 1985)18)... 

Figure 3b. The CH stretching region of monomeric solutions (0.08 M) of CgAO at Z equal 0,0.5 and 1.0.

Figure lib. Comparison of the CH stretching region of synthetic and experimental spectra of 0.40 M C12AO at Z equal 0.5. 

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