Aromatics CH stretchings

Overtone/combination band involving fundamentals in the 1810-1050 cm"1 (5.52-9.52 pm) range, aromatic CH stretch (high u), aliphatic CH stretch, ... 

Naturally, the bands in this region may well represent a blend of the (v = 1) —(v = 2) and (n = 2) — (n = 3) aromatic CH stretching transitions with overtones and combinations involving aromatic CC stretches as well as aliphatic CH stretches. Many PAHs which do not have aliphatic side groups show weak absorptions near these frequencies. For example, Fig. 6 shows that chrysene, pyrene and coronene all show substructure on a broad component. Chrysene and coronene show a peak at about 2910 and 2845 cm-1 while pyrene has a broad (weak) plateau from 2950-2880 cm-1, which is similar to the emission plateau observed from the astronomical object BD + 30°3639 [44]. In the laboratory spectra these are due to overtone and combination bands which have been perturbed sufficiently by solid state effects to absorb weakly [35, 36, 37, 38, 39]. The perturbations within the PAH clusters that are suspended in salt pellets induce IR activity and broaden the individual bands causing them to overlap. In free vibrationally excited PAHs, perhaps Fermi resonances between the overtones and combinations of C-C stretching vibrations with the highly excited C-H modes can sufficiently enhance the intensities of these presumably weak bands to produce the observed intensites. 

The IR spectra of the oil and asphaltene neutrals (35) exhibited no significant absorptions in the region 3200-3600 cm-1 except for H20 bands at 3620-3695 cm-1 in the matrix-isolation spectrum of the oil neutrals. Weak absorptions near 1700 cm-1 are indicative of minor amounts of ketones/ aldehydes in both neutral fractions. The absorptions at 2860, 2950, and 3050 cm-1 are ascribable to aliphatic and aromatic CH stretching. The band at 1600 cm-1 is characteristic of aromatic ring C=C. Thus, the oxygen-containing compounds in both neutral fractions are principally composed of ethers. 

An example of the former is seen in Hg(C9H7)Cl, which exhibits an aromatic CH stretching at 3060-3050 and an aliphatic CH stretching band at 2920-2850 cm The latter band should be absent in the jr-bonded complex Infrared spectra are reported for a mixed-valence-state complex, biferrocene (Fe, Fe ) picrate and bis(pentalenyl)Ni, whose structures are shown in Fig. IV-iifl and iV-llb, respectively. The spectrum of a triple-decker compound, [Ni2(Cp )i]BF4 (Cp CH3-CP) (Fig. IV-iic), is similar to that of Ni(Cp )2." ... 

OH stretch Aromatic CH stretch Asymmetric and symmetric stretch of CH2 C=C stretch of vinyl group... 

Infrared bands (frequency) cm Group assignments CHg symmetric stretch CHg asymmetric stretch Aromatic CH stretches 2,875 2,970 3,000-3,200 (1. 2)... 

Fig. 2 Transmission FT-IR of purified TPPT. Three spectral regions can be distinguished (i) 3150-3000 cm aromatic CH stretching vibrations, (ii) 2100-1660 cm overtone and combination bands due to the CH out-of-plane deformation vibrations, and (iii) 1600-400 cm fingerprint region...

Polymer Aromatic CH stretching Aliphatic CH stretching Ring stretching Methyl deformation Aromatic CH out-of-plane... 

Fig. 5.4. The infrared spectra in the CH stretching region are illustrated for the aryl-methyl, the aryl-methoxy, and the aryl-methylamino groups. A triplet of bands at 3100-3000 cm are caused by aromatic CH stretching vibrations. The rest of the bands are caused by the CHa group.

CH stretching frequencies associated with the benzene ring or other aromatic rings appear near 3030 cm Since this is in the region of the olefinic CH stretch, the aromatic CH vibration can be confused with the olefinic CH unless other aromatic vibrations are identified. The aromatic CH stretch is usually a band of medium to weak intensity. For some aromatic compounds several bands can be found near 3030 cm When a sodium chloride monochromator is used, the aromatic CH stretch may not be resolved from the stronger alkane CH vibrations. 

The aromatic -CH- stretch occurs just above 3000 cm" and the aliphatic just... 

A mixture of esters might be characterized by monitoring the absorbance due to the -CO- peak around 1700 cm", and a mixture of aromatic compounds by selecting the aromatic CH- stretch peaks just above 3000 cm". By plotting the... 

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