Triple bond molecule frequencies

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... 

In contrast to n-paraffins, which exhibit no or only a slight C NMR CSA, aromatics or hydrocarbons with double or triple bonds show a much larger anisotropy. Therefore, benzene (57) and 2-butyne 14) were chosen as suitable probe molecules to study molecular motions by C NMR lineshape analysis. Theoretical lineshapes for different motional states of benzene and 2-butyne molecules are depicted in Figs. 3 and 4. The proton-decoupled C NMR spectra were recorded by means of the homemade NMR spectrometer UDRIS (University of Leipzig) and a BRUKER MSL 400 (Central Institute of Physical Chemistry, Berlin) at frequencies of 22.6 and 100.6 MHz (9,14,57). 

It is very surprising that the Si-S distances as well as the Ge-S distances for the disulfides are shorter than the distances for the monosulfides, because for the similar carbon compounds the triple bond in CS is significantly shorter than the double bond in CS2 (151.9 pm/154.7 pm). This unexpected increase of bond strength from SiS to SiS and from GeS to GeS is now confirmed by similar changes of the force constants, which are strengthened by about 1 % in the Si-and 7 % in the Ge case. These force constant calculations are based on corrected frequencies because the frequencies of matrix-isolated species could not be compared with any data from ab initio calculations since the latter ones correspond to the harmonic potential of the gas-phase molecule. 

The corresponding CEO modes are displayed in Figure 12. The top row of color plots shows the lowest frequency mode (a) of the joara )ligomers. PI (a) centered at the triple bond shows maximum coherences and is delocalized over the entire molecule. The... 

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