Aromatic C-H absorption

A regression analysis applied to a series of coals, chars, and tars with widely differing ratios of aliphatic-to-aromatic hydrogen has been used to calibrate the aliphatic and aromatic C-H absorption intensities. 

Cracking. - Eberly et aP studied the coke formed on a cracking catalyst with IR. The fundamental C-H stretches in the 3100 to 2800 cm were important. The aromatic C-H absorption appears at 3050 cm and methylene groups at 2930 and 2860 cm The ratio of the absorbance of the infrared bands at 3050 and 2930 cm is a meassure of the aromaticity of the coke. In this case, it was found that the coke was formed by highly condensed aromatics of low hydrogen content. 

Solution The spectrum shows an intense absorption at 1725 cm- due to a carbonyl group (perhaps an aldehyde, -CHO), a series of weak absorptions from 1800 to 2000 cm-1, characteristic of aromatic compounds, and a C—H absorption near 3030 cm-1, also characteristic of aromatic compounds. In fact, the compound is phenylacetaldehyde. 

Compounds 1 and 2 were identified by FTIR and 13C-NMR. The 13C proton decoupled spectra for 1 and 2 are dominated by signals ranging from 62 to 195 ppm. The 13C chemical shift assignments were made based on comparisons with 4,4 -(hexafluoroisopropylidene)diphenol and from calculations based on substituted benzenes and naphthalenes.15 The 13C-NMR spectrum clearly showed that the Friedel-Crafts acylation of 1 by 4-fluorobenzoyl chloride yielded the 1,4-addition product exclusively. The 13C chemical shifts for 2 are listed in Table 8.1. The key structural features in the FTIR spectrum of2 include the following absorptions aromatic C-H, 3074 cnr1, ketone C=0, 1658 cm-1, aromatic ether Ar—0—Ar, 1245 cm-1, and C—F, 1175 cm-1. 

Formation of an amide is also indicated in the reaction of PCTFE with Cr(CO)6 and the primary amine, benzylamine. The infrared absorption spectrum shows an N-H stretch centered at 3400 cm, aromatic C-H stretches at 3063 and 3030 cm1, aliphatic C-H stretches at 2933 and 2876 cm1, a broad amide I/amide II band ranging from 1680-1580 cm1, and a C-N stretch at 1454 cm1. The C-Cl stretch at 970 cm1 also shows a significant decrease in... 

Infrared spectrum The IR shows a sharp peak around 3400 cm-1, possibly the N—H of an amine or the =C—H of a terminal alkyne. Because the MS suggests a nitrogen atom, and there is no other evidence for an alkyne (no C=C stretch around 2200 cm-1), the 3400 cm-1 absorption is probably an N — H bond. The unsaturated =C—H absorptions above 3000 cm-1, combined with an aromatic C = C stretch around 1600 cm-1, indicate an aromatic ring. 

The interstellar carbon grains contain both aliphatic and aromatic C—H and C—C bonds both are observed in absorption and emission in the ISM, but beyond this their exact composition is not known. Given the seemingly uniform elemental abundances in our local ISM we might expect that the dust composition would also be chemically uniform. However, the inferred elemental composition of silicates in the ISM... 

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