Alkanes infrared spectrum

The infrared spectrum of erythromycin is commonly used for its identification. Figure 2 shows the spectrum of a 75 mg./ml. chloroform solution. The bands at 1685 and 1730 cm- are due to the ketone carbonyl and the lactone carbonyl, respectively. The absorption peaks between 1000 and 1200 cm-1 are due to the ethers and amine functions. The CH2 bending is evidenced by peaks between 1340 and 1460 cm-, and alkane stretching peaks appear between 2780 and 3020 cm-. Hydrogen bonded OH and water appear as bands between 3400 and 3700 cm-1. 

The compound is soluble in acetone, chloroform, methylene chloride, and nitromethane. It is insoluble in alkanes and cold water and stable toward water in the cold but gives an acidic solution when boiled with water. The infrared spectrum shows a single band at 2510 cm.-1, about 50 cm.-1 higher wave number than in the monobromo compound. The nB spectrum gives a doublet 18.9 p.p.m. upfield from trimethyl borate Jb-h = 155 Hz. The proton spectrum in methylene chloride shows a sharp singlet at 2.91 p.p.m. downfield from external tetramethylsilane and 0.20 p.p.m. farther downfield than the monobromo compound. Boron-attached hydrogens are not detectable. 

A total of 310.3 g of methyl ester were pyrolysed to yield 204.4 g of liquid product which corresponds to a 65.9% actual liquid yield. The theoretical yield based on a typical Cie, C composition of soybean oil, and the y-hydrogen transfer mechanism is approximately 76%. Therefore, the yield based on this limitation is approximately 87%. "niis shows that random cracking of the ester chain does not play a significant role in the reaction. The infrared spectrum shows no carbonyl peaks at 1720 cm. Peaks appearing at 907 cm" and 965 cm arc probably absorptions due to terminal alkenes and trans alkenes, otherwise the spectrum looks like that of a typical alkane. Consistent with these results, elemental analysis gave 83.7% carbon, 14.56%... 

An alkane is unreactive toward most chemical reagents. Its infrared spectrum lacks the absorption bands characteristic of groups of atoms present in other families of organic compounds (like OH, C -Q,, C C, etc.). 

The infrared spectrum of an alkane is fairly uninformative because no functional groups are present and all absorptions are due to C-H and C-C bonds. Alkane C-H bonds always show a strong absorption from 2850 to 2960 cm", and saturated C-C bonds show a number of bands in the 800-1300 cm" range. Since most organic compounds contain saturated alkane-like portions, most organic compounds have these characteristic IR absorptions. The C-H and C-C bands are clearly visible in the three spectra shown in Figure 12.13. 

The limit of detection (LOD) for an acceptable GC-IR response for most compotmds is between about 1 and 20 ng (injected) per component, the actual value depending on the chemical nature of the analyte. The LOD is often defined with respect to the strongest band in the spectrum. Most bands in the infrared spectrum of nonpolar compounds are fairly weak and so these compounds tend to have the highest LODs, but even these compounds usually have at least one band in the spectrum with a high absorptivity. Examples include the C-H stretching bands of alkanes and the aromatic C-H out-of-plane deformation bands of polycyclic aromatic hydrocarbons. Detection limits also depend on the width of the GC peak the wider the peak, the more dilute the analyte and the higher the LOD. 

Shpol skii spectrofluorimetry has been used for the determination of PAHs in crude enviromnental sample extracts with minimum sample cleanup. This technique gives a vibrationally resolved fluorescence spectrum of samples dissolved in a suitable solvent (usually an -alkane) at cryogenic temperatures, e.g., 26 K. It combines the selectivity of an infrared spectrum with the sensitivity of fluorimetry, though the sensitivity suffers considerably from the presence of large amounts of interfering substances such as fatty components in crude extracts since these give a poor-quality matrix with a high sample absorbance. 

Let us first consider the vibrational spectra (infrared) of IPP in the melt (Figure 3-9a) [74], In this physical state, polymer chains possess a conformationally irregular structure like any liquid branched n-alkane. We expect the infrared spectrum to consist of relatively few bands easily identified as the group frequencies of CH3 and CH2 and CH groups. Other modes may be identified with caution, but their location is irrelevant to the present discussion. The experimental infrared spectrum of Figure 3-9a is in full agreement with the expectations. 

Let us take two samples of crystalline orthorhombic n-alkanes with an odd number of carbon atoms. They show properties identical to those observed for Cl 9. Let us make by suitable methods a mechanical mixture say of C21 and C23. The infrared spectra of the mechanical mixtures at low temperature are just the superposition of the spectra of the two independent components. Let us focus on the crystal held splitting, say of the doublets near 940 cm (C23) and 925 cm (C21) (Figure 3-59). If the mechanical mixture is brought near the solid-solid phase transition the infrared spectrum evolves with time. Time- and temperature-dependent spectra show that the doublets become singlets thus showing that chains have moved (Figure 3-59). The final product is a mixed crystal of C21 and C23 as also proved by parallel DSC studies. These studies were first reported by Ungar and Keller [156] and were re-examined and interpreted as reported in [155]. 

These modes give rise to characteristic bands found in the infrared spectrum of alkanes, such as in the spectrum of n-hexane shown in Figure 8.2. 

Alkanes show very few absorption bands in the infrared spectrum. They yield four or more C—H stretching peaks near 3000 cm" plus CH2 and CH3 bending peaks in the range 1475-1365 cm". ... 

Determine the structure for a compound with formula C3H5CIO. The IR spectrum, NMR, NMR, DEPT, COSY, and HETCOR (HSQC) spectra are included in this problem. The infrared spectrum has a trace of water that should be ignored (region from 3700 to 3400 cm ). The HETCOR spectrum should be carefully examined, for it provides very important information. You will find it helpful to consult Appendix 5 (alkanes and cyclic alkanes) for values of coupling constants. Determine the coupling constants from the NMR spectrum, except for proton c, and compare the calculated values to those shown in Appendix 5. Draw the structure of the compound, and label the protons on the structure. 

Fortunately, a way around the problem of mineral oil s infrared bands is a technique called the split mull method. The sample is first prepared as a mull in mineral oil and its spectrum is measured. Then a second mull of the sample is made using a mulling agent called Fluorolube , which is a mixture of long-chain fluorocarbons made by replacing all the C-H bonds in long-chain alkanes with C-F bonds. The infrared spectrum of Fluorolube is shown in Figure 4.10. 

Carbon atoms of an aromatic ring absorb in the range 110 to 140 8 in the 13C NMR spectrum, as indicated by the examples in Figure 15.16. These resonances are easily distinguished from those of alkane carbons but occur in the same range as alkene carbons. Thus, the presence of l3C absorptions at 110 to 140 8 does not in itself establish the presence of an aromatic ring. Confirming evidence from infrared, ultraviolet, or 1H NMR is needed. 

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... 

The chemistry of all of these molecules is fascinating but, concentrating on the origins of life, a detailed look at the organic species is appropriate to see what molecules are present and how they might have been formed. The only alkane detected directly in the ISM is methane but this is due to the problem of detection. All alkanes are non-polar and so do not have a pure rotation spectrum. However, there is one allowed vibration of methane that is infrared active and with the low moment of inertia of methane the vibration-rotation spectrum can be observed and a rotational progression identifies the molecule with confidence. 

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