Nitriles group frequencies

Infrared spectroscopy is an excellent tool in iminoborane chemistry, which readily permits, to distinguish between iminoboranes and nitrile-borane adducts and to identify monomeric and dimeric forms of iminoboranes. This event is due to the fact that the i>CN of CN multiple bonds absorbs outside the fingerprint region and can be considered to be a valuable group frequency even when mixed with other vibrational modes. In some cases other vibrations like NH, BH, B-halogen or B-S stretching modes are helpful for determining the structure of iminoboranes. 

Nitrile groups in the substrate may also cause problems. Minnaard, Feringa and de Vries reported the enantioselective hydrogenation of a range of substituted 2-acetamido-cinnamates at 5 bar pressure using Rh/MonoPhos. Whereas most substrates could be hydrogenated with turnover frequencies (TOFs) of between 200 IT1 and 600 h-1, the 4-cyano-substituted substrate was hydrogenated very slowly at this pressure with a TOF of only 4 h 1 [40]. 

In contrast to some of the aforementioned cases, the stretching frequency of the C N triple bond in the nitrile group shifts to the blue when this group accepts a proton in a H-bond. This shift amounts to some 20-30 cm when HCN is paired with HF, and the band is intensified by a factor between two and three. Also shifted toward the blue is the bending frequency of the HCN molecule. The red shift in the HF stretch within the donor molecule is considerably smaller than when HF donates a proton to the more basic amines, as... 

Because of the participation of the enamine double bond in the resonance of the aromatic ring of heteroaromatic /J-enamino esters, the group frequency character of the individual bands is low. Thus the El band is essentially vc=Q. Similarly, jS-enamino nitriles do not exhibit coupled vibrations since the nitrile absorption does not participate.24,61... 

In the IR spectra, the partially saturated heterocyclic /S-enamino nitriles do not exhibit the normal group frequencies that the corresponding esters display. The comparison of the 13C-NMR spectra of nitriles 299,300,302, and 305 with those of the esters 8,71, and 72 reveal for the nitriles a greater high-field shift of 27 ppm (Table III). As a consequence, it is concluded that in the enamino nitriles the double bond is more polarized than that of the corresponding esters several canonical forms can be discussed (Scheme 85). This difference in polarization (8, 71, and 72 versus 299, 300, 302, and 305) leads to several significant differences in the chemical behavior, which are briefly discussed in the following sections. 

Experimental evidence confirms this view the interaction of water with the nitrile group (of acetonitrile) leads to an increase of the stretching frequency of the C=N bond from 2254 to 2261 cm-1 (A >CN = 7 cm-1 9)), indicating a moderate stabilization of this bond. The hypsochromic shift of the C=N stretching frequency is diagnostic for interaction of the nitrogen lone pair electrons with an electron acceptor, and has been observed in numerous other complexes interaction of the C=N bonding -electrons with an acceptor, on the other hand, leads to a batho-chromic shift of i>cn (Sect. 4.1). 

We calculate an index of hydrogen deficiency of three. A quick glance at the infrared spectrum reveals the source of unsaturation implied by an index of three a nitrile group at 2260 cm (index = two) and a carbonyl group at 1747 cm (index = one). The frequency of the carbonyl absorption indicates an unconjugated ester. The appearance of several strong C—O bands near 1200 cm confirms the presence of an ester functional group. We can rule out a CM2 bond because they usually absorb at a lower value (2150 cm ) and have a weaker intensity than compounds that contain C=N. 

The typical FT-IR difference spectra are illustrated in Fig 3. It is found that the most significant spectra alteration caused by mixing involves a slight shift to lower frequency of the aromatic C-H out of plane bending vibration band at about 700 cm- and also C-Cl stretching band at about 670 cm". In the case of PVC/aSAN system, we could observe the additional peak shift to the lower value at about 2230 cm- which is caused by the specific interaction between nitrile group and a-hydrogen ofPVC. 

FTIR spectroscopy was used for the analysis of ultrathin organic films on metals. FTIR in the reflection mode (IRRAS) was used to study the interaction of ultrathin films of dicyandiamide (hardener of most one-pack epoxy resins) with various substrates, model ones such as gold or zinc and industrial ones such as steel and zinc-coated steels. Pure zinc surfaces and, to a lesser extent, zinc-coated steels are shown to react with dicyandiamide after heating at 180 C, as evidenced by the frequency shift of the absorption band characteristic for nitrile groups. Some mechanically tested specimens are then analysed, after failure, by FTIR microspectrometry. The spectra obtained, corresponding to the fracture initiation zone which is about 100 micrometers in diameter, indicate the presence of an ultrathin layer of modified polymer still covering the substrate. 28 refs. 

Nitriles, The very strong triple bond present in the nitrile group (as in the case of the alkynes) contributes to an unusually high stretching frequency, and the polar character of the group gives rise to very intense bands (Table 8.18 also see Chapter 8W, IR section. Fig. W8.33). [Pg.549]

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