Hydrocarbons infrared absorptions

Rasmussen, R. S. Vibrational frequency assignments for paraffin hydrocarbons infrared absorption spectra of the butanes and pentanes. J. chem. Phys. 16, 712—727 (1948). 

One has seen that the number of individual components in a hydrocarbon cut increases rapidly with its boiling point. It is thereby out of the question to resolve such a cut to its individual components instead of the analysis by family given by mass spectrometry, one may prefer a distribution by type of carbon. This can be done by infrared absorption spectrometry which also has other applications in the petroleum industry. Another distribution is possible which describes a cut in tei ns of a set of structural patterns using nuclear magnetic resonance of hydrogen (or carbon) this can thus describe the average molecule in the fraction under study. 

Allyl Free Radicals. Ayscough and Evans (3) have recently studied, by ESR measurements, the types of allylic free radicals produced by gamma-irradiation of several monomeric olefins. In irradiated polyethylene the allyl free radical is quite stable, persisting for several months at room temperature (31). The presence of these allyl free radicals is most noticeable in the case of high density polyethylene, and this type of free radical is undoubtedly the cause of the slow oxidation of polyethylene at room temperature, which lasts for 40 or more days after irradiation (10). Williams and Dole (40) could observe little if any oxidation of low density polyethylene when it was exposed to air after irradiation. By oxidation we mean formation of carbonyl groups as detected by infrared absorption studies at 1725 cm"1. Parenthetically, it should be noted that adding an oxygen. molecule to a free radical produces initially another type of free radical, a peroxy free radical, but in this paper we shall not discuss free radicals of this or any other types except those of hydrocarbons. 

Although infrared absorption analysis of hydrocarbon mixtures was described by Lecomt and Lambert (34), the extensive application of this technique to the examination of petroleum products awaited the commercial availability of a practical instrumental unit and adequately described methods such as those of Brattain and Beeck (11) for a two component mixture and Brattain et al. (12) for a multicomponent mixture of hydrocarbon gases. By such methods the possible qualitative constituents of the sample must, of course, be known and their number limited to a maximum probably simultaneously present. 

Supercritical fluid extraction uses a supercritical fluid (Box 25-2) as the extraction solvent.20 C02 is the most common supercritical fluid because it is inexpensive and it eliminates the need for costly disposal of waste organic solvents. Addition of a second solvent such as methanol increases the solubility of polar analytes. Nonpolar substances, such as petroleum hydrocarbons, can be extracted with supercritical argon.21 The extraction process can be monitored by infrared spectroscopy because Ar has no infrared absorption. 

The dipolar MSSR applies strictly to a flat metal surface. However, the consideration by Pearce and Sheppard (93) that adsorbed layers are typically a few angstroms (tenths of nanometers) thick in relation to the diameters of larger metal particles in catalysts (up to tens of nanometers) led to the consideration that the MSSR could have substantial effects on the intensities of infrared absorptions from adsorbed species on metal catalysts with large particles. It has been estimated that parallel modes of vibration will have their infrared absorption bands substantially attenuated at metal particle diameters of greater than 2 nm (94). This is proving to be a very important consideration in the interpretation of the infrared spectra from adsorbed hydrocarbon species on metal catalysts (20, 95, 96) and has recently become widely accepted as valid (52, 54, 57, 62, 97). 

Fig. 5. A summary of the infrared absorption bands exhibited by hydrocarbon ligands on metal atoms in various model compounds. Surface species on metals may give absorptions varying by ca. 50 cm 1 from the band positions in the model-compound spectra in the fingerprint region below 1400 cm. The patterns of band-positions and intensities are significant. M indicates MSSR-allowed modes for an analogous species on a flat surface when the adsorbed species is on a site of high symmetry (--) indicates other absorptions that may occur for adsorption on less symmetrical sites or on small metal particles, vs—very strong s—strong ms—medium strong m—medium mw—medium weak w—weak.

Francis, S. A. Absolute intensities of characteristic infrared absorption bands of aliphatic hydrocarbons. J. chem. Phys. 18, 861—865 (1950). 

Furthermore, the conformation and orientation of the hydrocarbon chains of MS in the MS-C20 binary and MS-C2o-AL18 ternary systems were investigated by using infrared absorption spectroscopy. In this respect, deuterated arachidic acid (C2o-d) and deuterated n-octadecane AL %-d) were utilized to separate infrared bands due to the hydrocarbon chains of MS from those arising from C2o and AL18. Fig. 26 shows polarized infrared spectra A of 10-layer LB films of pure cadmium arachidate (CdC20), MS-C20- binary and MS-C20-t/-AL18-t/... 

Fig. 28(b) depicts polarized infrared absorption spectra of 10-layer LB films of pure CdC2()-r/, and the MS-C2o binary and MS-C20-AL18-r/ ternary systems [80,82]. In the case of CdC20-r/ LB film, peaks at 2193 and 2089 cm-1 are assigned to the CD2 antisymmetric and symmetric stretching modes of the hydrocarbon chain, respectively, and their peak positions are characteristic of the stW-trans conformation of the hydrocarbon chain. The LB film of the MS-C20 binary system does not show the peak, as a matter of course. The film of the MS-C20-AL18 ternary system yields the peaks at 2194 and 2089 cm suggesting the presence of AL 18-d with the all-/ra//,v conformation. 

Table 6.33 Main infrared absorption lines of hydrocarbons (referring to a transparency <50%)...

The hydrogen-bonding group of each polymer has been taken as equivalent to that of the parent mononrer. (The hydrogen-bonding tendency can be assigned qualitatively in the order alcohols > ethers > ketones > aldehydes > esters > hydrocarbons or setniquantitatively from infrared absorption shifts of CH rOD in a reference solvent and in the liquid of interest (7J.)... 

No gas-phase photolyses have yet been reported with these diazirines. Pyrolysis of the cycloheptyldiazirine yields a mixture of hydrocarbons, and the relative yields of these products are very close to the values obtained by the pyrolysis of diazocycloheptane. Photolysis of these diazirines in the liquid phase yields a hydrocarbon mixture similar to that obtained by pyrolysis, but with small increases in some of the minor products. The photoisomerization reaction leading to the normal diazo compound is readily observed for these two diazirines since the diazo compounds formed are relatively stable. In both cases, during photolysis of the (colorless) diazirines, a deep orange solution develops, and ultraviolet and infrared absorption spectra indicate the formation of the diazo compounds. Photolysis of cycloheptyldiazirine in the presence of acetic acid yields 47% of cycloheptylacetate, which indicates that the photoisomerization reaction under these conditions is a major primary reaction. Under the same conditions cyclooctyldiazirine yields 28% of the corresponding acetate. 

Pendleton Y. J., Sandford S., AUamandola L., Tielens A. G. G. M., and Sellgren K. (1994) Near infrared absorption spectroscopy of interstellar hydrocarbon grains. Astrophys. J. 437, 683-696. 

Table 13.3 lists infrared absorption frequencies characteristic of various groups. We shall look more closely at the infrared spectra of hydrocarbons in Sec. 13.15 and, in following chapters, at the infrared spectra of other families of compounds. 

Slightly or non polar aproticsolvents like ethersand hydrocarbons. The absorption spectrum is observed in the infrared domain with a maximum at wavelengths higher than 2000 nm for example, 2200 nm for tetrahydrofuran. 

V vs. SHE by surface enhanced Raman spectroscopy, and on a Cu deposited Pt electrode by infrared absorption spectroscopy.2° These facts established tliat CO is intermediately formed at a copper electrode during CO2 reduction and further reduced to hydrocarbons and alcohols. 

See Table 1 of the 1956 paper by Clark, Hogan, Banks, and Lanning, Ind. Eng. Chem. 48,1152, which contained this statement about the earliest polypropylene made from Phillips catalyst "Contains a solid fraction, insoluble in hydrocarbons, which is identical in X-ray diffraction and infrared absorption to the isotactic polymer described by Natta."... 

The concentrations of NO, NO2, N2O and propene were measured at steady state in the outlet gas flow using analysers based on chemiluminescence for NO (Cosma Topaze 2000), UV-Visible absorption for NO2 (Rosemount Binos 1004) and Infrared absorption for N2O (Cosma Beryl 100). The rate of conversion of NO to N2 was obtained from the difference between the total conversion rate of NO and the rate of NO oxidation. N2O was never detected at a significant level. Hydrocarbon concentrations were measured with a FID (Cosma Graphite 55). 

When two or more olefinic groups occur in the hydrocarbon molecule, the infrared absorption spectrum shows the additive and combined absorption of the unsaturated... 

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