Aliphatic stretching region bands

Table V. Rotated Matrix of Factor Loadings for Components Analysis of FTIR Absorption Bands in the Aliphatic Stretching Region...

Aliphatic stretching region in vitrinite, rotated matrix of factor loadings for components analysis of FTIR absorption bands, 1l4t... 

Inspect the C—H stretching region and identify the bands as either of aliphatic or aromatic/olefinic origin. 

Absorption bands in the typical C—H stretching region at 3000-2870 cm-1 usually showing two maxima at 2925 and 2855 cm-1 related to CH2 and CH3 aliphatic groups. These bands are well defined in the spectra obtained from microbial biomass of soils and there can be assigned to cell wall and capsular polysaccharides (Filip, 1978) 27). But they are also common in spectra of other biological materials. 

Table II. Band Assignments for the Aliphatic Stretching and Aromatic Out-of-plane Bending Regions...

In the spectra of aliphatic ethers, the most characteristic absorption is a strong band in the 1150-1085 cm-1 region because of asymmetrical C—O—C stretching this band usually occurs near 1125 cm-1. The symmetrical stretching band is usually weak and is more readily observed in the Raman spectrum. 

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. 

Since several bands may appear in the C—H stretch region, it is probably a good idea to decide only whether the absorptions are acetylenic (3300 cm ), vinylic or aromatic (>3000 cm ), aliphatic (<3000 cm ), or aldehydic (2850 and 2750 cm ). Further interpretation of C—H stretching vibrations may not be worth extended effort. The C—H bending vibrations are often more useful for determining whether methyl or methylene groups are present in a molecule. 

The most intense band is the C=0 stretch, at 1730 cm indicating that the aldehyde carbonyl is part of the aliphatic portion of the molecule. Looking at the C—H stretching region, the sharp aldehydic C—H bands appear at 2725 and 2825 cm . The doublet... 

Figure 16. The resolution of the aliphatic C—H stretching region into five bands.

Primary amines show characteristic first overtone bands at 1450, 1550 and 1000 nm which represent the first and second overtones of N-H stretching bands. Tertiary amines produce no N-H overtones, but do produce C-H and 0-H stretching combination bands at 1260-1270 nm. The first overtones of the N-H stretching bands of aliphatic amines are shifted to lower wavelengths. Primary amides may be characterized by combination bands at 1930-2250 nm and an N-H stretching overtone band at 1450-1550 nm. Secondary amides produce overtone bands in the 1350-1550 nm region and combination bands in the 1990-2250 nm region. 

The most intense band is the C=0 stretch, at 1730 cm", indicating that the aldehyde carbonyl is part of the aliphatic portion of the molecule. Looking at the C-H stretching region, the sharp aldehydic C H bands appear at 2725 and 2825 cm". The doublet appears due to resonance with an overtone of the aldehydic C-H bend at 1390 cm". This is called Fermi resonance and is always seen in aldehydes. The sharp peaks above 3000 cm" are the aromatic C-H stretching peaks and the peaks between the aromatic and aldehydic peaks are due to the aliphatic C-H stretches. The sharp... 

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