First Overtone Region

L. England Kretzer and W. A. P. Luck, Band analysis of CH3OH and CH3OD H bond complexes in the first overtone region. J. Mol. Struct. 348, 373 376 (1995). 

A. Watanabe, J. L. Hunt, and H. L. Welsh. Structure of the pressure induced infrared spectrum of hydrogen in the first overtone region. Can. J. Phys., 49 860, 1971. 

Figure 6.2-21 Vibrational intensity fi of C H modes of n-alkanes, plotted as a function of the number of C- H bonds (a) C H stretching first overtone region between 5300 and 6100 cm (b) C H stretching second overtone region between 7500 and 9000 cm. ...

The general absorptions of methylene groups are illustrated in Figure 2.7, a spectrum of n-decane. 23.1 First Overtone Region — Linear Molecules... 

Methylene groups in linear, aliphatic molecules have two primary peaks at about 5800 cm" (1723 nm) and 5680 cm" (1762 nm) in the first overtone region. The 5800-cm" peak is generally thought to be a combination band, " reported as The 5680-cm" peak is considered to be a pure... 

The 5800-cm peak is usually the strongest peak in the first overtone region of a series of linear hydrocarbons. Tosi and Pinto provide a formula for locating this peak for a series of linear hydrocarbons 5856-85 x weight-fraction of CH2, or about 5800 cm for hexane. They also mention that this peak splits into two closely spaced peaks possibly due to the influence of adjacent methyl groups. The absorptivity of this combined peak does not regularly increase with chain length, probably because it has contributions from two sources. 

The weaker methylene peak in the first overtone region was said to be at 5671 + - 3 cm for linear hydrocarbons. This peak was thought to have contributions from both methyl and methylene groups (Tosi and Pinto), although others have assigned a 5680-cm band to be both the first overtone of the methylene symmetric stretch and of the asymmetric stretch shifted by Fermi resonance (Ricard-Lespade et al.). More recently, Parker et al. have discussed the origins of this peak in terms of local mode theory. 

The C-H stretch first overtone region of cyclohexane has two strong peaks at 5697 cm (1755 nm) and 5791 cm (1727 nm). A number of smaller, additional peaks were also seen by curve resolution. The two strongest peaks are probably 2Va and 2Vg with the intensity of the symmetric band being intensified by Darling-Dennison resonance. 

The first overtone of a free hydroxyl group in dilute CCI4 solution or a low-density gas is at about 7090 cm (1410 nm). This peak is at different positions for primary, secondary, and tertiary alcohols, as seen in Figure 5.1. Primary and secondary butanols can be split into doublets by rotational isomerization. The splits are better seen in Figure 5.2, in the second derivation spectra of the same spectral region. Maeda et al. observed an additional peak in the first overtone region when they subtracted the spectrum at a lower temperature from that at a higher one. They felt that temperature effects further separated species that were weakly bonded to the carbon tetrachloride solvent and a terminal free OH of a self-associated species. 

As shown in Figure 8.1, primary and secondary amines are distinctly different in the first overtone region near 6600 cm. Primary amines have a doublet, and secondary a single peak. Tertiary amines have no peak as they have no N-H functionality and are not shown in the figure. The asymmetric and symmetric NH-stretching peaks occur at 6553 and 6730 cm (1625 and 1486 nm), respectively, in butyl amine in carbon tetrachloride. The first overtone of secondary amines has only one band near 6530 cm (1530 nm). 

The NH-stretching bands of aromatie amines such as aniline show a doublet in the first overtone region, but it is shifted to lower wavelengths relative to aliphatic amines. Figure 8.2 compares the near-infrared spectrum of aniline in CCI4 with that of n-butyl amine. The asymmetric vibration occurs... 

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