Skeletal vibration

/soPropyl and te/t.-butyl structures. Skeletal vibrations are usually very sensitive to changes in the immediate environment of the vibrating group and hence considerable frequency shifts can be caused. However, these considerations do not apply to branched 

Experimentally they have found that in paraffins up to and 

Similar calculations by the same authors for the isopropyl type skeletons indicate that the V2 and frequencies should occur near 1170 and 1145 cm and experimental evidence again confirms this. In the series 2-methylpropane to 2-methylnonane, they find one frequency to be constant in the range 1170—1167 cm , whilst the second falls steadily from 1170 cm in the first to 1142 cm in the last. The structure (CH3 )2C with no free hydrogen atom on the central carbon gives only a single band in this region [54] at 1195 cm . A second band near 1210 cm has been observed in some cases, but it is more variable in position [64]. 

These correlations have also been fully substantiated by the observations of Rasmussen [28]. Whilst differing in the interpretation of these bands, he has given empirical data obtained on a large number of branched-chain paraffins which confirm that bands at the positions indicated can be associated with these different types of branched-chain structure. These correlations appear to hold, also, for many non-hydrocarbons provided no oxygen atoms are attached 

In addition to these correlations, Simpson and Sutherland have pointed out that a third skeletal vibration ( 4) can also be predicted 

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Katritzky and Topsom have reviewed the information available, largely from infrared and n.m.r. studies, concerning the distortion of the tt-electron system in the benzene ring brought about in the ground state by substituents. Of particular interest is the observation that both n.m.r. studies (of m- F and chemical shifts) and infrared investigations (of the intensities of bands due to certain skeletal vibrations) suggest that the value of Taft s [Pg.226]

Armarego et have determined the infrared spectra of the four parent pyridopyrimidinos (148) in the solid phase as KBr discs, and have comiiared them with other di-, tri-, and tetraazanaphthalenes. Thirteen in-plane skeletal vibrations and ten CH bending vibrations... 

The most characteristic feature of the infrared spectra of all 5-mono- and -di-substituted-amino-l,2,3,4-thiatriazoles is a strong band in the 1540-1590 cm range, which without doubt is due to the C=N and N=N stretching vibrations of the heteroaromatic ring system. Various infrared bands between 889 and 1122 cm have been assigned to skeletal vibrations of the thiatriazole ring and a band... 

Katritzky, Topsom, and co-workers (14) have reported correlation of the integrated intensities of the 1600 cm" benzene skeletal vibration of substituted... 

The gold(III) complexes, ]Au(C N C)L ]" and [Au2(C N C)2(P P)[(C104)2 are emissive in acetonitrile at low temperature. The frozen-state (77 K) emission spectra of the mononuclear complexes [Au(C N C )L [" show well-resolved vibronic structures with spacings in the 1100-1300 cm range, which correlate with the skeletal vibrational frequency of the tridentate C N C ligand. By comparing the emission... 

Broclawik, E., Datka, J., Gil, B. et al. (2000) T-O-T skeletal vibration in CuZSM-5 zeolite IR study and quantum chemical modeling, Phys. Chem. Chem. Phys., 2, 401. 

Diffraction patterns and FTIR spectra of skeletal vibrations of the ZSM-5 and ferrierite zeolites indicated high crystallinity of the analyzed samples. The strong band with a chemical shift of about 55 ppm in the 27Al MAS NMR spectra of hydrated zeolites indicated the presence of more than 97 % Al in the framework in tetrahedral coordination the very low intensity of the peak at 0 ppm indicated less than 3 % rel. of Al in octahedral coordination. 

The prominent IR peaks for 1,2,4-thiadiazoles were attributed as follows to ring skeletal vibrations (1560-1590, 1490-1550 cm-1), to ring breathing and CH-in-plane deformations (1215-1270, 1080-1185, 1020-1050 cm-1), and to CH out-of-plane deformations ( 735 and 795-860 cm-1) <1982AHC285>. 

Pyda and co-workers [49, 60] measured the reversible and irreversible PTT heat capacity, Cp, using adiabatic calorimetry, DSC and temperature-modulated DSC (TMDSC), and compared the experimental Cp values to those calculated from the Tarasov equation by using polymer chain skeletal vibration contributions (Figure 11.7). The measured and calculated heat capacities agreed with each other to within < 3 % standard deviation. The A Cp values for fully crystalline and amorphous PTT are 88.8 and 94J/Kmol, respectively. 

The transfer of the expected ranges is particularly satisfactory for skeletal vibrations, whereas it is probably less precise in the case of C—H vibrations, since the vibrations of the H-atoms are more strongly infiuenced by the added proton, and since three additional fundamental vibrations can also arise. For this reason the assignment of the C—H vibrations in the intermediate frequency range is less reliable than for the other bands. 

In a study on acid-leached mordenites, Vansant and coworkers found a linear correlation between the frequency of a skeletal vibration mode and the framework... 

Al(HE), Ga(HE) as well as In(HE) porphyrin are typical porphyrins incorporated with a tervalent metal ion Characteristic Q and B bands in the visible and near-ultraviolet region, respectively, arise from the (7T,7T ) excitations in the porphyrin ring with only minor perturbation from the outershell electrons of the central metal ion. The Q band is of forbidden character, however, the Q band can borrow the intensity by vibronic couplings from the allowed B band (30). The intensity of the Q(1,0) band is much less sensitive to the peripheral substituents, the axial ligands and the central metal ions, while that of the Q(0,0) band without excitation in the skeletal vibrational modes is rather sensitive to various substituents. 

Far-infrared 700-200 14.3-50 Lattice vibrations Skeletal vibrations Fleavy atoms... 

When there are several bonds of similar strength between atoms of similar mass, we get several skeletal vibrations occurring over a wide frequency range an example is the C—C skeletal vibrations of organic molecules. 

Skeletal vibrations, 266, 268 Slater determinant, 48 Slater-type orbitals, 65 s levels, 181, 287 Snow, 328n... 

Now, in aromatic hydrocarbons intramolecular skeletal vibrations, rather than C—H vibrations, dominate the vibronic coupling contribution to the term J m = — . Furthermore, intermolecular vibrations will have negligible effect on the coupling of the electronic states of interest. Thus, in the case of internal conversion, where the (relatively large) matrix elements are solely determined by intramolecular vibronic coupling, no appreciable medium effect on the nonradiative lifetime is to be expected. On the other hand, intersystem crossing processes are enhanced by the external heavy atom effect, which leads to a contribution to the electronic coupling term. 

The infrared spectra of the cycloproparenes are characterized by a weak band that appears between 1660 and 1690 cm"1 due to a combination of the aromatic double bond stretch with the three-membered ring skeletal vibration. Angular fused cyclo-propa[a]naphthalene (10) has the highest value (1687 cm"1) while for linear 11 it is more usual at 1673 cm"1, and cyclopropa[6]anthracene falls between these at 1678 cm"1. The... 

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