The C O Stretching Vibration

The reaction coordinate is the C-O stretch vibration of the CO molecule in its transition state. The rate constant is... 

Molecules possess discrete levels of rotational and vibrational energy. Transitions between vibrational levels occur by absorption of photons with frequency v in the mid-infrared range (Table 8.1). The C-O stretch vibration, for example, is at 2143 cm 1. For small deviations of the constituent atoms from their equilibrium positions, the potential energy V(r) can be approximated by that of the harmonic oscillator ... 

Comparing with the normal mode calculation and the experimentally determined value for CO/Pt(lll) below, it seems likely that for the ontop bonded molecules the anharmonic coupling is to the frustrated translation. As expected, d(o is then negative as the C—O stretch vibration frequency decreases when going away from the ontop position. 

The C—O stretching vibration of formaldehyde is reduced from 1 746 cm 1 in the Sq state to 1 183 cm 1 in the S, slate because the strength of the C—O bond decreases when the antibonding tt orbital is populated. 

Fig. 15.3 Identification of the synwietnes of the C—O stretching vibrations (represented as vectors) for Fe(CO)j. The reducible representation. T, is derived by counting the number of vectors remaining unmoved during each operation of the point group (see Appendix D for character table). Its irreducible components are obtained by application of Eg. 3.1...

The spectroscopic properties of ethers are unexceptional. Like alcohols, they have no electronic absorption beyond 185 nm the important infrared bands are the C—O stretching vibrations in the region 1000-1230 cm-1 their proton nmr spectra show deshielding of the alpha hydrogens by the ether oxygen (6Hcaoc 3.4 ppm). The mass spectra of ethers and alcohols are very... 

The carbonyl complex 33 is obtained in a clean displacement reaction when carbon monoxide is passed through a solution of 32 in methanol. Due to the increased charge on the cation, the product precipitates in the process. The rather low frequency of the C O stretching vibration in the IR spectrum of the solid (KBr disc) at 1960 cm-1 points to a strong Fe-CO interaction (100), as expected for the highly basic NN4 ligand environment. Similarly low values (1940-1960 cm-1) were reported for the pentaamine iron(II) complexes... 

The applications of PM-IRRAS also include fatty acids, phospholipids, and protein conformations. Desbat and co-workers reported on the variation of the dissociation of a Langmuir monolayer of arachidic acid at the air-water interface as a function of the subphase pH and for several cations (Cd2+, Ca2 +, Mg2 +, and Na+) with the help of the PM-IRRAS method [92]. Fig. 14 shows the PM-IRRAS spectra of Langmuir monolayer of deuterated arachidic acid in the presence of CdCb as a function of the subphase pH. At low subphase pH (pH = 3.5), the spectrum only presents absorption bands related to the acid form, i.e., the C = O stretching vibration (v(C = O)) and the OH bending (<5(0-H)) located at 1720 and 1270 cm respectively. The frequency position of the v(C = O) is characteristic of a hydrogen-bonded carbonyl group. As the subphase pH is increased, the arachidic acid is progressively deprotonated to... 

Owing to the fact that the carbonyl frequency falls in the region of C=C absorption, the identification of the C—O stretching vibration has sometimes been established by isotopic substitution with 180 <71AHC(13)161,p.220,72BSF1385,73BSF3339). 

In the region of the C—O stretching vibrations, an important increase in absorbance was observed with maxima at 1060 cm-1 (a, (3-unsaturated ether bridges and a, (3-unsaturated alcohols), 1094 cm 1 (saturated secondary alcohols and saturated ethers) and 1175 cm-1 (lactone). 

The positions of the C—O stretching vibrations in the ions may be affected by interactions with solvents or counterions, and solid and solution spectra may differ slightly. 

Detailed vibrational assignments have been carried out on arene chromium and arene molybdenum tricarbonyl complexes (18, 19). Splitting of the E band in the carbonyl region was observed for substituted benzene chromium tricarbonyl complexes but not in (CgHg)Cr(CO)3 itself, showing that the concept of local symmetry (Cg ) is of very restricted validity when discussing the C—O stretching vibrations in such complexes (18). 

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