Infrared Spectroscopy of Hydrocarbons

Hydrocarbons contain only carbon-carbon bonds and carbon-hydrogen bonds. An infrared spectrum does not provide enough information to identify a structure conclusively (unless an authentic spectrum is available to compare fingerprints ), but the absorptions of the carbon-carbon and carbon-hydrogen bonds can indicate the presence of double and triple bonds. 

Stronger bonds generally absorb at higher frequencies because of their greater stiffness. Carbon-carbon single bonds absorb around 1200cm ,C=C double bonds absorb around 1660 cm , and C=C triple bonds absorb around 2200 cm.  

As discussed for the octane spectrum, C — C single bond absorptions (and most other absorptions in the fingerprint region) are not very reliable. We use the fingerprint region primarily to confirm the identity of an unknown compound by comparison with an authentic spectrum. 

The effect of conjugation is even more pronounced in aromatic compounds, which have three conjugated double bonds in a six-membered ring. Aromatic C=C bonds are more like 11 bonds than true double bonds, and their reduced pi bonding results in less stiff bonds with lower stretching frequencies, around 1600 cm . 

Alkanes, alkenes, and alkynes also have characteristic C—H stretching frequencies. Carbon-hydrogen bonds involving sp hybrid carbon atoms generally absorb at frequencies just below (to the right of) 3000 cm those involving sp hybrid carbons absorb just above (to the left of) 3000 cm . We explain this difference by the amount of character in the carbon orbital used to form the bond. The x orbital is closer to the nucleus than the p orbitals, and stronger, stiffer bonds result from orbitals with more 5 character. 

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The Infrared Region 515 12-4 Molecular Vibrations 516 12-5 IR-Active and IR-lnactive Vibrations 518 12-6 Measurement of the IR Spectrum 519 12-7 Infrared Spectroscopy of Hydrocarbons 522 12-8 Characteristic Absorptions of Alcohols and Amines 527 12-9 Characteristic Absorptions of Carbonyl Compounds 528 12-10 Characteristic Absorptions of C—N Bonds 533 12-11 Simplified Summary of IR Stretching Frequencies 535 12-12 Reading and Interpreting IR Spectra (Solved Problems) 537 12-13 Introduction to Mass Spectrometry 541 12-14 Determination of the Molecular Formula by Mass Spectrometry 545... 

Pinto, A. Near-infrared spectroscopy of hydrocarbon functional groups. Spectrochim. Acta 28A, 585-597 (1972). 

Tosi, C. and A. Pinto, Near-Infrared Spectroscopy of Hydrocarbon Functional Groups. Spectrochim. 

Hudgins, D. M., and S. A. Sandford, Infrared Spectroscopy of Matrix Isolated Polycyclic Aromatic Hydrocarbons. 1. PAHs Containing Two to Four Rings, J. Phys. Chem. A, 102, 329-343 (1998a). 

The acid, base, and neutral Lewis base fractions consist of polar molecules capable of hydrogen bonding and, therefore, of intermolecular association. These polar fractions, which constitute nearly two-thirds of the 675°C+ residuum, have high concentrations of heteroelements in comparison to the nonpolar aromatic and saturate hydrocarbons, as shown in Table IX for the residuum from a Russian crude oil. Infrared spectroscopy of the acid fraction revealed mostly pyrroles with phenols but only traces of... 

Reed 332) has reported that reaction of ethylene oxide with the a,(a-dilithiumpoly-butadiene in predominantly hydrocarbon media (some residual ether from the dilithium initiator preparation was present) produced telechelic polybutadienes with hydroxyl functionalities (determined by infrared spectroscopy) of 2.0 + 0.1 in most cases. A recent report by Morton, et al.146) confirms the efficiency of the ethylene oxide termination reaction for a,ta-dilithiumpolyisoprene functionalities of 1.99, 1.92 and 2.0j were reported (determined by titration using Method B of ASTM method E222-66). It should be noted, however, that term of a, co-dilithium-polymers with ethylene oxide resulted in gel formation which required 1-4 days for completion. In general, epoxides are not polymerized by lithium bases 333,334), presumably because of the unreactivity of the strongly associated lithium alkoxides641 which are formed. With counter ions such as sodium or potassium, reaction of the polymeric anions with ethylene oxide will effect polymerization to form block copolymers (Eq. (80) 334 336>). 

Dougherty TP, Heilweil EJ. Transient infrared spectroscopy of (jj5-C5H5)Co(CO)2 photoproduct reactions in hydrocarbon solutions. J Chem Phys 1994 100(5) 4006-4009. 

Wu G, Kaltchev M, Tysoe WT (1999) The kinetics and infrared spectroscopy of Cj hydrocarbons adsorbed on clean and oxygen-modified Mo(lOO). Surf Rev Lett 6 13... 

Structural sensitivity of the catalytic reactions is one of the most important problems in heterogeneous catalysis [1,2]. It has been rather thoroughly studied for metals, while for oxides, especially for dispersed ones, situation is far less clear due to inherent complexity of studies of their bulk and surface atomic structure. In last years, successful development of such methods as HREM and STM along with the infrared spectroscopy of test molecules has formed a sound bases for elucidating this problem in the case of oxides. In the work presented, the results of the systematic studies of the bulk/surface defect structure of the oxides of copper, iron, cobalt, chromium, manganese as related to structural sensitivity of the reactions of carbon monoxide and hydrocarbons oxidation are considered. 

Reed has reported that reaction of ethylene oxide with the a,(a-dilithiumpoly-butadiene in predominantly hydrocarbon media (some residual ether from the dilithium initiator preparation was present) produced telechelic polybutadienes with hydroxyl functionalities (determined by infrared spectroscopy) of 2.0 + 0.1 in most cases. A recent report by Morton, et al. confirms the efficiency of the ethylene oxide termination reaction for a,ta-dilithiumpolyisoprene functionalities of 1.9, 1.92 - i reported (determined by titration using Method B of ASTM... 

Spectroscopic studies have been performed on aqueous dispersions of di (10,12-tricosadiynoyl) phosphatidylcholine before and after polymerization with ultraviolet light. Non-resonance Raman and infrared spectroscopies of both the polymer and monomer reveal the structure of the hydrocarbon chains and head groups of the lipids. 

Oomens J, Tielens AGGM, Sartakov BG, Von Helden G, Meijer G (2003) Laboratory infrared spectroscopy of cationic polycyclic aromatic hydrocarbon molecules. Astrophys J 91 968-985... 

Most hydrocarbon resins are composed of a mixture of monomers and are rather difficult to hiUy characterize on a molecular level. The characteristics of resins are typically defined by physical properties such as softening point, color, molecular weight, melt viscosity, and solubiHty parameter. These properties predict performance characteristics and are essential in designing resins for specific appHcations. Actual characterization techniques used to define the broad molecular properties of hydrocarbon resins are Fourier transform infrared spectroscopy (ftir), nuclear magnetic resonance spectroscopy (nmr), and differential scanning calorimetry (dsc). 

Infrared Spectroscopy (ir). Infrared curves are used to identify the chemical functionality of waxes. Petroleum waxes with only hydrocarbon functionality show slight differences based on crystallinity, while vegetable and insect waxes contain hydrocarbons, carboxyflc acids, alcohols, and esters. The ir curves are typically used in combination with other analytical methods such as dsc or gc/gpc to characterize waxes. 

Methods utilizing characteristic physical properties have been developed for several chlorinated hydrocarbon insecticides. Daasch (18) has used infrared spectroscopy for the analysis of benzene hexachloride. By this means it is possible to determine the gamma-isomer content, as well as that of the other isomers of technical benzene hexachloride, provided the product is substantially free of the higher chlorinated cyclohexanes. 

Infrared diode laser spectroscopy has been used for the measurement of hydrocarbon and CO concentrations in exhaust (13, 14, 15). The adsorption path length, and thus the absorption cell volume, required for hydrocarbon measurement is rather large, limiting the time-resolution of the measurement. The absorption path length required for CO measurement, however, is relatively short and approximately equal to the diameter of a standard exhaust pipe. This allows CO to be measured with high time-resolution by an infrared laser beam passed through an... 

Topnir Not a chemical process but an instrumental process for on-line monitoring of hydrocarbon process streams by infrared spectroscopy. Developed by BP and offered for license in 1997. 

Infrared spectroscopy has been applied to the determination of particulate organic carbon in non-saline sediments, aliphatic hydrocarbons and total organic carbon in saline sediments and mixtures of organics in sludges. 

Concawe [8] have described a method for the determination of aliphatic hydrocarbons in soil based on carbon tetrachloride extraction followed by infrared spectroscopy or gas chromatography. 

Analysis for total petroleum hydrocarbons (EPA Method 418.1) provides a one-number value of the petroleum hydrocarbons in a given environmental medium. It does not, however, provide information on the composition (i.e., individual constituents) of the hydrocarbon mixture. The amount of hydrocarbon contaminants measured by this method depends on the ability of the solvent used to extract the hydrocarbon from the environmental media and the absorption of infrared light (infrared spectroscopy) by the hydrocarbons in the solvent extract. The method is not specific to hydrocarbons and does not always indicate petroleum contamination, since humic acid, a nonpetroleum material and a constituents of many soils, can be detected by this method. 

Therefore, for infrared spectroscopic methods, the total petroleum hydrocarbons comprise any chemicals extracted by a solvent that are not removed by silica gel and can be detected by infrared spectroscopy at a specified wavelength. The primary advantage of the infrared-based methods is that they are simple and rapid. Detection limits (e.g., for EPA 418.1) are approximately 1 mg/L in water and 10 mg/kg in soil. However, the infrared method(s) often suffer from poor accuracy and precision, especially for heterogeneous soil samples. Also, the infrared methods give no information on the type of fuel present in the sample, and there is little, often no information about the presence or absence of toxic molecules, and no specific information about potential risk associated with the contamination. 

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