Methylene group infrared absorption

Eischens and Pliskin have interpreted the infrared spectra of ethylene chemisorbed on nickel dispersed on silica 32). When introduced to a surface previously exposed to hydrogen, ethylene gave rise to absorption bands which correspond to the C—H stretching frequencies of a saturated hydrocarbon (3.4-3.5 p) and a deformation associated with a methylene group (6.9 p). A weak band at 3.3 p was attributed to an ole-finic C—H. Treatment of the chemisorbed ethylene with hydrogen caused the spectrum to change to one which was interpreted as due to an adsorbed ethyl radical. Apparently in the presence of hydrogen most of... 

The infrared spectra of l,4-anhydro-3,5-0-methylene- and -2-0-methyl-DL-xylitol have been studied.60 The 2-methyl ether was obtained by converting l,4-anhydro-3,5-0-methylene-DL-xylitol into its monomethyl ether, and then hydrolyzing off the methylene group. A methyl ether prepared from the known l,4-anhydro-3,5-0-isopro-pylidene-2-O-methyl-DL-xylitol proved to be identical with this compound, thus establishing at the same time that the methylene group in the known acetal is attached to 0-3 and 0-5 of 1,4-anhydro-DL-xylitol. The methylene group, having a 1,3-dioxolane structure, was characterized by an absorption band at about 2800 cm 1. 

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. 

The nmr spectra of the problem is misleading at first glance. The triplet at 6 1.2 is comprised of three peaks not in the 1 2 1 ratio. However this can be explained if the ir N-H absorption is kept in mind. The hydrogen of a secondary amine will absorb at a position of 1.2 ppm. This would cause an overlap and produce a disproportionate triplet. The sharp singlet at 6 7.2 confirms the presence of a monosubstituted benzene alluded to by the compound s infrared spectra. The peak at 6 3.8 with a relative area of two would be indicate of a methylene group situated next to electron withdrawing substituents. 

The simplest vibrational motions in molecules giving rise to the absorption of infrared radiation are stretching and bending motions. Illustrated in Figure 11.3 are the fundamental stretching and bending vibrations for a methylene group. 

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