Symmetrical stretching methylene

FIG. 10 Vibrational sum frequency spectrum of saturated monolayers of dilauroyl- (DLPQ, dimyristoyl- (DMPC), dipalmitoyl- (DPPC), and distearoyl-phosphatidylcholine (DSPC) at the D2O-CCI4 interface at ambient temperature in the region of the methylene and methyl symmetrical stretches. (From Ref 139, copyright American Chemical Society.)... 

Amines. In dilute solution primary amines show two absorption bands, one near 3500 cm -1 and the other near 3400 cm-1, arising from the asymmetric and symmetric stretching vibrations of the two NH bonds (cf. the vibrations of a methylene group, Fig. 3.1). Secondary amines show just one band near 3300 cm-1 due to the single N—H stretching vibration, while tertiary amines do not absorb in this region. These characteristic absorptions allow one to dis-... 

Figure 2.10 shows the methylene and methyl symmetric stretch region of the spectrum for each headgroup before (solid squares) and after (solid triangles) the exposure of the monolayer to halothane. For each spectrum shown, there is a small increase in the overall intensity when halothane is present. This increase occurs across the entire spectrum for each of the phospholipids smdied. We believe that the small change in intensity... 

FIGURE 2.10. Representative spectra of dipalmitoyl phospholipid monolayers at the CCU/D2O interface under the ssp polarization scheme showing the methyl and methylene symmetric stretch (a) DPPC, (b) DPPE, (c) DPPG, (d) DPPS. Spectra of the monolayers are shown in solid squares. Spectra of the monolayers with halothane are shown with solid triangles. The lines ate fits to the data. From Ref. [62]. 

A review of infrared (and Raman) spectra of cyclopropenes has been presented (see also Ref. 316). In cyclopropene itself a weak symmetrical stretch (Aj) involving the vinyl hydrogens occurs at 3076 cm" and it was proposed that the C-H stretching vibrations that involve the methylene carbons of cyclopropene should approximate to those of cyclopropane. 

The absorption bands at 2920 and 2860 cm are evident in the spectra of most humic substances, usually superimposed on the shoulder of the broad O—H stretching band. They are generally more pronounced in humic acids than in fulvic acids. These bands are attributed to the asymmetric and symmetric stretching vibrations, respectively, of aliphatic C—H bonds in methyl and/or methylene units (Theng et al., 1966). This assignment is consistent with the observed increase in absorbance of these bands upon methylation of the humic substance (Wagner and Stevenson, 1965 Wershaw et al., 1981). 

Primary-amine combination (N-H symmetric stretch + C-N stretch) Primary-amine combination (N-H symmetric stretch + deformation) Primary-amine combination (N-H asymmetric stretch + deformation) Methylene first overtones (C-H stretch)... 

The FT-IR-ATR absorption spectrum of the control polypropylene (untreated) is shown in Figure 1. It is a typical polypropylene spectrum with absorption bands due to asymmetric and symmetric stretching of CH3 and CH2 groups around 2900 cm-1. The absorption bands at 1460 nd at 1380 cm-1 represent the asymmetric and symmetric bending of CH3 respectively. Absorption bands at 2878 cm-- - (CH3 stretching) and at 841 cm-- (Methylene rocking modes) suggest that the polypropylene membrane is of the isotactic form. 

However, the IR spectrum for high density PE in Figure 16.6 shows some differences, since there are three main signals for a molecule having the same chemical composition. Band (A) represents the symmetrical stretching for methyl and methylene groups, and band (B) corresponds to the symmetric methylene bending. The last one... 

Methyl asymmetric bend Methyl symmetric bend Methylene symmetric bend Lactone C-O-C asymmetric bend Ester C-O-C asymmetric bend Lactone C-O-C symmetric stretch Ester C-O-C symmetric stretch Alcohol C-OH stretch Trisubstituted olefinic C-H wag... 

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