C—N Stretching Vibrations

Aromatic amines display strong C—N stretching absorption in the 1342-1266 cm1 region. The absorption appears at higher frequencies (shorter wavelengths) than the corresponding absorption of aliphatic amines because the force constant of the C—N bond is increased by resonance with the ring. 

Characteristic strong C—N stretching bands in the spectra of aromatic amines have been assigned as in Table 3.4. 

FIGURE 3.29. Octylamine. A. The N—H stretch, hydrogen-bonded, primary amine coupled doublet asymmetric, 3372 cm-1. Symmetric, 3290 cm-1. (Shoulder at about 3200 cm1, Fermi resonance band with overtone of band at C.) B. Aliphatic C—H stretch, 2925, 2850 cm-1 SCH2, 2817 cm-1. C. The N—H bend (scissoring) 1617 cm-1. D. SsCH2 (scissoring), 1467 cm-1. E. The C—N stretch, 1073 cm-1. F. The N—H wag (neat sample), -900-700 cm-1. 

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Gold (I) cyanide [506-65-0] M 223.0, m dec on heating. The lemon yellow powder is sparingly soluble in H2O and EtOH but soluble in aqueous NH3. It is obtained by heating H[Au(CN)2] at 110°. Wash well with H2O and EtOH and dry at 110°. It has an IR band at v 2239cm typical fo C=N stretching vibration. [Handbook of Preparative Inorg anic Chemistry (Ed. Brauer) Vol II 1064 7965.] CARE may evolve HCN. 

The only doubly bonded tin compound for which the IR spectrum has been reported is the stannaketenimine [2,4,6-(CF3)3C6H2]2Sn= C=N[2,4,6-(CH3)3C6H2)]. The C—N stretching vibration (2166 cm-1) is shifted relative to that of mesityl isocyanide (2118 cm-1) this phenomenon is also observed for isocyanide-transition-metal complexes.87... 

For the series of silver complexes with cyanide, the C-N stretching vibrations are observed as follows. The species containing three or four cyanide ions are observed only in solutions containing high concentrations of CNT... 

Compared to the structures of Li+-water solvates, the structures of Li+-acetonitrile solvates are in general less studied. The Li+ ion was found to be four coordinate with the use of different techniques, e.g., by NMR where acetonitrile was gradually replaced by water in a 1.6 M solution of LiC104 (130), or based on IR intensities measured for the acetonitrile C-N stretching vibration (131,132). Even mixed coordination of a counter ion and acetonitrile were reported to be four coordinate, viz., in [Li(CH3CN)3Br] for 0.58 M LiBr in CH3CN (133). Extensive... 

For further investigations f-BuNC, which is isolobal to CO, was used. With PhLi and t-BuLi, the characteristic vibrational mode of the lithium isonitrile adduct (2135 cm ) was observed at a lower wavenumber than that of the free isonitrile (2179 cm ). Unfortunately, n-BuLi did not undergo complexation. As indicated by the C=N stretching vibrational mode at 1510 cm, only f-BuLi—CN—R reacted further to afford the lithiated Schiff base up to —20°C (equation 2) . ... 

Doubts about C=N stretching vibrations of dithiazolines (53) and (54) and of the 3-imino-dithiazolidine (44) appeared, when Dickore et al. <62AG(E)594> reported that they can be distinguished as they have between 1550-1590 and 1630 cm respectively, but later workers assigned a 1600 cm for compounds which were claimed to be of type (44) though... 

Also present in this region are the C—C and C=N stretching vibrations (Scheme 3.9), but these are generally much weaker than the carbonyl absorptions. 

X-Ray diffraction shows that the [Pt(CN)6]2 ion is regular octahedral with linear Pt—C—N bonds.3"2 The IR and Raman spectra of K2[Pt(CN)6] have C—N stretching vibrations at higher frequencies and C—N force constants which are larger than the corresponding divalent complexes.303,304 This correlates with less n back-donation from the metal to the empty n orbitals of the cyanide ligand in the PtIV complexes. 

Bands resulting from the primary and secondary N—H bending vibrations appear near 1650 cm-1 and 1550 cm-1 respectively in the solid phase, and the large difference in these amide II bands enables primary and secondary amides to be distinguished. The 1550 cm -1 band is not a simple N—H bending mode, but is believed to result from coupling of this deformation with a C—N stretching vibration. 

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