Aromatic stretching, FTIR

Aromatic positions, deuterium-hydrogen exchange reaction of tetralin-di2 and diphenylmethane, I62t,l63t Aromatic stretching, FTIR of vitrinite, 103-12 Aromatic-to-aliphatic ratios, carbon-13 NMR, 80-95 Aromaticity, 73... 

Aliphatic stretching, FTIR of vitrinite, 103-12 Alkyl phenols, Py-MS, 153f Analytical analyses of demineralized coals, density fractions, 71t Aromatic adjacent hydrogen in... 

Before the FTIR data were analyzed together with coalification parameters in a components analysis, it was first necessary to select which variables to use. In general, the number of variables should not exceed one-third of the number of samples (in this study the maximum number is 8). Components analyses were performed on data for the aliphatic stretching and aromatic out-of-plane bending regions of the infrared spectrum in order to eliminate those variables that did not provide new information. 

While the detection of the Si-H and Si-C modes indicates HREELS can probe the buried molecule/silicon interface, in general this method will be most sensitive to the terminal groups at the vacuum/monolayer interface. This is illustrated in Fig. 9 where spectra for several modified surfaces with different terminal functionalities are shown. In each case this terminal group is tethered to the surface via a Cio alkyl linker yet the spectra are significantly different. This is particularly evident in the spectra for the thienyl terminated surface in which the aromatic C-H stretch is clearly observed. In contrast this mode is quite small in the FTIR spectra, which are dominated by the contributions of the alkyl linker chain [51]. The observation of strong terminal group modes in the HREELS spectra indicates that these functional groups are likely present at the surface of the film and not buried back towards the H-terminated surface. This is consistent with their availability for sequential reactions as discussed in the previous section. 

Samples of the support and catalyst were subjected to propane (2020 Pa) at various temperatures in the FTIR environmental cell. By 673 K the principal bands observable are those due to carboxylate and aromatic species (Table 3). Bands due to C-H stretch were not observed, and the intensity of the bands obtained from the catalyst sample was greater than those from the alumina by approximately a factor of 2.5. Once again there is a similarity between the species present on the alumina and those on the catalyst but with the amounts being significantly higher on the catalyst. 

Although the polycyclic aromatics detected by GCMS would give strong C-H stretch bands in the gas phase [8], if they were adsorbed with the ring system parallel to the surface then the intensity may be below detection limits. However the FTIR spectra also revealed carbonate and carboxylate species on the alumina surface. These species will also contribute to the differential between the carbon retained by the catalyst and that removed under regeneration. 

Fourier transform infrared (FTIR) spectroscopy and Raman spectroscopy have also been used to authenticate polyanhydride structures. Aliphatic polymers absorb at 1740 and 1810 cm while aromatic polymers absorb at 1720 and 1780 cm All the polyanhydrides show methylene bands because of deformation, stretching, rocking, and twisting. Aside from being used to ascertain polyanhydride structures, these techniques can be used to determine degradation progress, by monitoring the area of carboxylic acid peak (1770-1675 cm ) with respect to the characteristic anhydride peaks over time. 

OH defonnation vibration can be found in the region 1410 - 1260 cm . Strong C-0 valence vibrations between 1150 and 1040 cm" overlap with aromatic fingerprint bands at 1225 - 950 cm". CH3 symmetric deformation vibrations occur in the region 1370 - 1190 cm". Ofter authors ascribe the 1049 cm-1 region to C-OH and C-C stretching mode (27, 28). However, it is not excluded that the FTIR spectra may contain useful information located in too weak peaks not visible by direct visual inspection. More specific chemical and spectroscopic application knowledge is required to fully interpret this plot. 

The FTIR spectra of the soluble coke showed bands at 3010, 1480 and 780 cm assigned to C-H and C-C stretching and C-H and C-C deformation respectively, which are typical of aromatics. The spectra also showed typical absorption bands for aliphatic hydrocarbons at 2960 and 2800 cm for CH3 and at 2930 cm for CH2 groups [18], The coke band due to the presence of polyolefins and/or polycondensed aromatics [19, 20] was present as a shoulder at 1585 cm No significant difference was noted among the spectra. Figure 2 illustrates the curves obtained. The presence of aromatics was confirmed by UV spectra by the presence of a band in =262 nm [21],... 

Jacobs et al. [724] introduced the FTIR measurement of the shift of the OH stretching band upon benzene adsorption as a measure of the acid strength of the hydroxy groups. Jacobs [725] also provided a theoretical reasoning for this effect. Similarly, O Malley [794] developed an electrostatic model for predicting the shift of typical IR bands upon adsorption of aromatics on the respective zeolitic OH groups. 

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