C---H Stretching Vibrations

An ultrashort mid-IR pulse excited a C-H stretching vibration (-3000 cm ) of neat acetonitrile at 300 K. The loss of C-H stretching energy occurred in 3 ps. Only 1% of that energy was transferred to the C N stretch (2250 cm ), where it remained for -80 ps. Most of the energy was lost from the C-H stretch by the process,... 

The inequality of the C—H bonds in the radical cation implies that all C—H bonds do not have the same force constants. In a simplistic approximation, the zero-point vibrational energy (ZPVE) of a C—H stretching vibration will be proportional to (k/mn), where k is the force constant of the C—H bond and j// is the mass of the hydrogen nucleus. The effect on the ZPVE of replacing one proton by a deuteron will hence depend on the deuteration site, such that the ZPVE will be lowered more if the deuteron occupies a site with a larger fcrce constant, i.e. a shorter bond. This, in general, means a site with low unpaired spin density. 

Hunt JH, Guyot-Sionnest P, Shen YR. 1987. Observation of C H stretch vibrations of mono-layers of molecules. Optical-sum frequency generation. Chem Phys Lett 133 189-192. 

Five bands are observed in the region near 3000 cm-1 corresponding to C—H stretching vibrations. (The band at 2947 cm-1, which appears as a shoulder in Fig. 15, is seen as a separate peak when the spectrum is observed on an expanded transmission scale.) Detailed identification of these bands will be deferred, but the weak band at 3055 cm-1 suggests that the hydrocarbon fragment is olefinic. 

Quantitative calculations of the IMECs of the C=C stretching and C-H bending bands confirmed this trend (Table 1). Furthermore, for Ca2+ and Mg2+ cations the IMEC values exceed those for the free molecules, while for the Na+ ions there is little effect. This indicates a stronger polarization of the C=C bond in ji-complexes of propene with bivalent than with monovalent cations. As follows from Table 1 the IMECs of the C-H stretching vibrations of propene adsorbed by different cations are strongly decreased in comparison with the free molecule. The ratio of the IMECs for C=C and C-H stretching bands is increased for propene adsorbed by Mg2+ cations in comparison with the ratio obtained for the free molecule. 

C-H-stretching vibrations C=0-stretching of 5-membered ring lactam (cyclol)... 

Complex of strong bands due to the overlapping C-H stretching vibrations of the various methyl and methylene groups. 

Figure 9.29 XPS, FTIR and RBS of a CrO,ySi02/Si( 100) after polymerization of ethylene at 160 °C all reveal the presence of a significant amount of polyethylene, visible in the C Is peak in XPS, the symmetric and asymmetric C-H stretch vibrations of CH2 groups in transmission IR, and a C peak in RBS (adapted fromThiine etal. [92]).

Example Calculate the approximate frequency of the C—H stretching vibration from the following... 

The Hamiltonian operator that preserves the symmetry of the molecule can now be constructed. Since all the bonds in Figure 6.1 are equivalent, the most general lowest order Hamiltonian for C-H stretching vibrations of C6Hg is... 

C-H stretching vibrations of C6H6 are therefore characterized by five quantities AH, Ahh, A, h, Xj1//, and h- If. instead of C6H6, one wishes to study C6D6, which has the same symmetry D6h of C6H6, the same Hamiltonian (6.24) will apply except that now the five quantities AH, AHH, X jj and the... 

For the synthesis of MgPz (2), the alkylated maleonitrile was treated with Mg butanolate. Because of the template effect of magnesium, maleonitrile molecules cyclotetramerize to form magnesium porphyrazine. MgPz is soluble in number of common solvents like chloroform, acetone etc. and little soluble in ethanol and methanol. The absence of CN peaks in IR spectram can easily be attributed to the cyclotetramerization, and the only strong peak was observed at 2,922 cm for C-H stretching vibration of 3-metylbutane groups. 

The earliest experiments with lasers in absorption spectroscopy were performed with the high-gain infrared line X = 3.39p of the He-Ne laser the first gas laser Several authors Miscovered that this laser line is absorbed by many hydrocarbon molecules, causing a vibrational-rotational transition in a band which belongs to the excitation of a C-H stretching vibration . ... 

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