Alkanes infrared spectroscopy

Infrared radiation, electromagnetic spectrum and, 419, 422 energy of. 422 frequencies of, 422 wavelengths of, 422 Infrared spectroscopy, 422-431 acid anhydrides, 822-823 acid chlorides, 822-823 alcohols. 428, 632-633 aldehydes, 428. 730-731 alkanes, 426-427 alkenes, 427 alkynes, 427 amides. 822-823 amines, 428, 952 ammonium salts, 952-953 aromatic compound, 427-428, 534 bond stretching in, 422... 

One of the initial spectroscopic methods applied to stationary-phase characterization was Fourier transform infrared spectroscopy (FTIR). This originated from several important studies of phase conformational order in crystalline n-alkanes conducted in the late 1960s and early 1980s by Snyder, Maroncelli, and coworkers [111-114], In this work, assignments of C—H bond wagging modes were associated with chain... 

Excited-state Mg atoms react with methane and other alkanes via H atom abstraction in the gas phase (equation 1). By studying the vibrational states of the MgH product, information on the mechanism has been inferred. It has been found that regardless of the alkane, RH (and thus the C—H bond strength), the vibrational state distributions are essentially identical. This suggests that long-lived vibrationaUy excited [RMgH] complexes are not intermediates for equation 1 in the gas phase. The situation is quite different for excited-state Mg atoms reacting with methane under matrix conditions, where the insertion product (equation 2) is sufficiently stable for analysis via infrared spectroscopy ". Calcium atoms have been shown to insert into the C—H bonds of cycloalkanes. ... 

The oxidative addition of alkanes to Rh1 and Ir1 species CpML is very facile. In the case of the tris(pyrazolyl)borate complex Tp Rh(CO)2 [Tp = HB(2,4-Me2pyr)3], the lifetimes of the intermediates were determined by ultrafast time-resolved infrared spectroscopy. In this case de-chelation of one of the pyrazolyl arms was found to precede the C—H oxidative addition step. The proposed intermediates for R—H addition and their lifetimes are shown in Fig. 21-1.127... 

Tungstated zirconia (WZ) catalysts have been proposed as viable candidates for alkane isomerizations, especially those heavier than C4 [1]. In this work, alcohol dehydrations were used to rank the acidity of WZ with respect to that of HY zeolite, and to evaluate the ability of these catalysts to resist coking during a reaction that yields an olefin molecule as the primary product. The results from temperature-programmed reaction and infrared spectroscopy studies allowed us to gain some insight into the relative stability of WZ. 

Infrared spectroscopy has been extensively used in elucidating the microstructure of plasma-polymerized materials. Earlier works (54, ) have shown that short alkane segments and various types of vinyl groups are the predominant structural groups observed. 

Molecules react because they move. Atoms have (limited) movement within molecules— you saw in Chapter 3 how the stretching and bending of bonds can be detected by infrared spectroscopy, and we explained In Chapter 4 how the a bonds of alkanes (but not the n bonds of alkenes) rotate freely. On top of that, in a liquid or a gas whole molecules move around continuously. They bump into each other, into the walls of the container, maybe into solvent... 

The recrystallization of S-layer proteins at phosphoethanolamine monolayers on aqueous subphases has been also studied on a mesoscopic scale by dual label fluorescence microscopy andFourier transform infrared spectroscopy (FTIR) [110]. It has been shown that the phase state of the lipid exerts a marked influence on the protein crystallization. When the surface monolayer is in the phase separated state between fluid and crystalline phase, the S-layer protein is preferentially adsorbed at the boundary line between the two coexisting phases and crystallization proceeded underneath the crystalline phase. Crystal growth is much slower under the fluid lipid and the entire interface is overgrown only after prolonged protein incubation. In turn, as indicated by characteristic frequency shifts of the methylene stretch vibrations on the lipids, protein crystallization affects the order of the alkane chains and drives the fluid lipid into a state of higher order. However, the protein does not interpenetrate the lipid monolayer as confirmed by x-ray reflectivity studies [105-107]. 

Figure 6.2. Polarized reflection infrared spectroscopy to determine structure and order in alkane thiol SAMs (a) comparison of theoretical and experimental C-H stretching IR spectra for octadecyl thiol adsorbed on to gold (b) effect of temperature on increasing the disorder in the alkane chain...

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