Triple bonds infrared spectroscopy

Much earlier information on the structure of diazonium ions than that derived from X-ray analyses (but still useful today) was obtained by infrared spectroscopy. The pioneers in the application of this technique to diazonium and diazo compounds were Le Fevre and his school, who provided the first IR evidence for the triple bonds by identifying the characteristic stretching vibration band at 2260 cm-1 (Aroney et al., 1955 see also Whetsel et al., 1956). Its frequency lies between the Raman frequency of dinitrogen (2330 cm-1, Schrotter, 1970) and the stretching vibration frequency of the C = N group in benzonitrile (2255 cm-1, Aroney et al., 1955). In substituted benzenediazonium salts the frequency of the NN stretching vibration follows Hammett op relationships. Electron donor substituents reduce the frequency, whereas acceptor substituents increase it. The 4-dimethylamino group, for example, shifts it by 103 cm-1 to 2177 cm-1 (Nuttall et al., 1961). This result supports the hypothesis that... 

The differences in selection rules between Raman and infrared spectroscopy define the ideal situations for each. Raman spectroscopy performs well on compounds with double or triple bonds, different isomers, sulfur-containing and symmetric species. The Raman spectrum of water is extremely weak so direct measurements of aqueous systems are easy to do. Polar solvents also typically have weak Raman spectra, enabling direct measurement of samples in these solvents. Some rough rules to predict the relative strength of Raman intensity from certain vibrations are [7] ... 

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. 

The molecules OCO, SCS, and OCS are linear. Bond lengths are given in Tables 21.5 and 21.6. In carbon dioxide the carbon-oxygen bond is intermediate in length between a double and triple bond. The studies of CO2 and CS2 by high resolution infrared spectroscopy provide an example of the use of this method for molecules which cannot be studied by the microwave method because they have no permanent dipole moment. The structure of the CS2 molecule has also been studied in the crystalline state. (C—S, 1-56 A). Under a pressure of 30 kbar CS2 polymerizes to a black solid for which a chain structure has been suggested. ... 

The analysis of the resulting copolymers were established by H NMR, infrared and UV—visible spectroscopies. Table 26 shows the copolymerization results by metal catalysts. The H-NMR spectra of both the monomer and the polymer are shown in Figure 33. As the polymerization proceeded, the acetylenic proton peak at around 1.96 ppm disappeared and a new vinylic proton peak appeared in the aromatic region. Also, the IR spectra of the polymer showed no absorption peaks at 3290 and 2140 cm , which are expected to be present for the acetylenic carbon—hydrogen bond stretching and carbon—carbon triple bond stretching in the monomer, respectively. 

Alkynyliodonium salts can be conveniently identified by IR and NMR spectroscopy. In the infrared spectrum, the most characteristic absorption is the triple bond band between 2120 and 2190 cm . In the C NMR spectrum, the most distinctive signals are the acetylenic a- and p-carbons, with the former generally between 10 and 40 ppm and the latter at 110-120 ppm. 

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. 

Adsorbed CO2 can be reduced via equation (2.11). At a potential below 0.4 V versus RHE, CO2 reduction is favored because there is sufficient Pt- OH j promoting CO2 electroreduction. Beden et al. [56] investigated the nature of reduced CO2 by infrared (IR) spectroscopy and found that the reduction of CO2 involved reaction with adsorbed hydrogen. They also found that reduced CO2 yielded a significant amount of highly coordinated adsorbed CO species rather than the linearly bonded CO species formed by direct CO adsorption. However, the exact structure and adsorption form of these surface species have not yet been clarified they could be linear, bridge, or triple-bonded CO [56-61]. Studies have also found CO/COOH radicals [21], COOH ds, as well as COHads [58,62-64] during CO2 reduction. 

Infrared spectroscopy is helpful in identifying terminal alkynes. Characteristic stretching bands appear for the alkynyl hydrogen at 3260-3330 cm and for the C=C triple bond at 2100-2260 cm . There is also a diagnostic Pq-h bending absorption at 640 cm ... 

Infrared spectroscopy is useful for determining the presence and identity of functional groups. These spectra measure the frequency of bending and stretching of bonds where the bond dipole changes with the movement. The stretching vibrations of double and triple bonds in alkenes and alkynes... 

---