Vibrational spectroscopy isomers distinguished using

Where a molecule is fairly symmetrical different structures can be distinguished using vibrational spectroscopy. This method has been used, for example, to characterize geometrical isomers of substituted octahedral complexes. The point groups and symmetry classes of the normal v(C0) vibrations for octahedral complexes M(CO) L. are listed in Table 5.6. Sometimes infrared spectroscopy... 

It is a straightforward process to distinguish between them using techniques such as NMR or vibrational spectroscopy. But when we think a little deeper we realize that each of the two isomers can be drawn in different ways. Structure 2.1, a square-based pyramid, can also be drawn as a trigonal bipyramid, with the O atom in either the equatorial (2.III) or axial position (2.IV), and stmcture 2.II has O-F staggered with respect to the S-F bonds, but in principle it could also be eclipsed (2.V). 

This sort of analysis provides a powerful use of spectroscopy to aid in the identification of molecular structure through the application of symmetry. If we had made a sample of difluorobenzene and believed it to be a pure isomer of either the 1,4- or 1,2-form, vibrational spectroscopy would provide one way to distinguish which isomer we had made. 

Infrared spectroscopy may be used to distinguish between cis and trans isomers of compounds. The structural symmetry of the molecule is used to determine the point group, the vibrational selection rules then being applied to determine which vibration bands are observed. 

Ultraviolet photoelectron spectroscopy (UPS) of anionic C provides information on the electron affinity (EA), and electronic and vibrational structures of the corresponding neutral species. The size dependence of EAs and the vibrational fingerprints are useful to distinguish isomers when combined with mass spectrometry. In 1988 Yang et al. reported the first experimental indication of the presence of monocyclic carbon clusters C in laser vaporization of graphite in helium gas [17]. For clusters C ... 

Infrared (IR) spectroscopy is particularly helpful to study organometallic compounds [8, 9] especially carbonyl complexes. This is also true in aqueous solutions, although one has to take into consideration the water absorbances in the IR spectral region. The CO stretching vibrations are intense and characteristic of the chemical environment. In the case of several carbonyls in the same molecule, the intensity ratios give structural information and can help to distinguish isomers. In water the useful spectral domain is limited by solvent absorbances and one must use a shorter optical pathlength and compensate for water absorbance. 

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