The Triple-Bond Region

Explain why the presence of a triple bond is much easier to detect in the 1R spectrum of 1-hexyne than it is in the spectrum of 3-hexyne. 

Nitriles Nitriles are readily identified by the absorption due to the CN triple bond that appears in the region of 2260—2220 cm-1. This band is relatively strong because the bond is polar. 

Mosl types of spectroscopy can be used for quantitative analysis because the intensity of an absorption band—that is, the amount of light absorbed at a particular wavelength—is proportional to the amount of compound in the sample. A group of chemists at the University of Denver has developed a device that can measure the amount of carbon monoxide and hydrocarbons in the exhaust of an automobile by remote sensing— that is, in the street as the automobile passes by. 

Poorly maintained automobiles pollute by emitting carbon monoxide and hydrocarbons, products of incomplete combustion. Because carbon monoxide is very poisonous and hydrocarbons contribute to the formation of smog, it is desirable to minimize the emission of bolh of these pollutants. 

The amounts of carbon monoxide, hydrocarbons, and carbon dioxide are recorded by a computer, and a video camera records a picture of the license plate of the car. The accompanying picture shows the video screen with the percent CO in the exhaust listed at the lower left, the percent hydrocarbon in the middle, and the percent C02 at the right. This particular vehicle was a high polluter, emitting 10.35% CO, 0.36% hydrocarbons, and 7.69% C02. The emission of a well-maintained, low-polluting vehicle contains about 0% CO, 0% hydrocarbons, and 15% C02. Because about 10% of the vehicles emit about 65% of the pollution, the identification and repair of these high polluters could substantially reduce the air pollution caused by automobiles. 

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The triple bond region (2500-2000 cm 1), where contributions from gas phase CO (2143 cm 1) and linearly adsorbed CO (2000-2200 cm 1) are seen,... 

The carbonyl groups in nickel carbonyl may be replaced by isonitriles as well as by phosphines etc. 162) in general all the carbonyl groups are replaced in the direct reaction, but a compound (MeNC)3Ni(CO) has been obtained. Cotton and Zingales have measured the infrared spectra of a few of these compounds in the triple-bond region (46), and some interesting facts emerge. The frequencies are shown in Table III and it is clear that... 

Cyanopentakis(benzyl isonitrile)iron(II) bromide, which represents a new class of iron isonitrile complexes, was investigated in some detail. This complex is diamagnetic and dissociates in nitrobenzene into two univalent-univalent ions as indicated by cryoscopic and conductivity measurements. It exhibits two peaks in the triple bond region of the infrared spectrum one at 2200 cm.—1 assigned to the isonitrile groups and another at 2092 cm.-1 assigned to the cyano group. The structure proof of cyanopentakis (benzyl isonitrile) iron (II) bromide is ... 

The band in the triple bond region at 2150-2100 cm-1 is much stronger for 1-hexyne than it is for the more symmetrical 3-hexyne. In addition, the =CH band near 3300 cm 1 in the spectrum of I-hexyne confirms the presence of the triple bond. 

Infrared spectroscopy is one of the most powerful tools for functional studies of hemoproteins reactive to external hgands with infared absorptions in the triple bond region (1900-2200 cm ) where the background level due to absorptions of proteins and water molecules is quite low as described above. However, recent improvement in the sensitivity and stability of the FTIR apparatus with an MCT detector has enabled infrared spectroscopic examination of the protein moiety also. In fact, one of the most sensitive methods for monitoring the dissociation of a COOH group is infrared spectroscopy. 

All infrared spectra have many absorptions, but those useful for identifying specific functional groups are usually found in the region from 1500 cm to 3300 cm" Pay particular attention to the carbonyl region (1670-1780 cm" ), the aromatic region (1660-2000 cm" ), the triple-bond region (2000-2500 cm" ), and the C-H region (2500-3500 cm" ). 

Recent results obtstined at higher spinning speeds reveal the presence of some residual absorption in the triple bond region (95 to 102 ppm) for the material with 6 Br per repeat unit. 

This is illustrated by the example of propyne (2)2 The electronic density in the triple bond region of 2 is essentially symmetrically distributed with... 

The application of infrared difference spectroscopy as demonstrated in their work provides a new way to study metal-protein complexes with ligands such as carbon monoxide, cyanide, azide, and others, which absorb in the triple-bond region. 

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