Benzene infrared absorption frequencies

Compounds of zirconium and hafnium metal tetrahalides with the bidentate ligands ( )4As2C2H4 and ( )4P2C2H4 were prepared 447) by the reaction of the tetrahalide and the ligand in a suspension in benzene. These are presumably species with a coordination number of eight. The infrared absorption frequencies in the 460-250 cm region are tabulated in Table VII. 

Except in simple cases, it is very difficult to predict the infrared absorption spectrum of a polyatomic molecule, because each of the modes has its characteristic absorption frequency rather than just the single frequency of a diatomic molecule. However, certain groups, such as a benzene ring or a carbonyl group, have characteristic frequencies, and their presence can often be detected in a spectrum. Thus, an infrared spectrum can be used to identify the species present in a sample by looking for the characteristic absorption bands associated with various groups. An example and its analysis is shown in Fig. 3. 

The Hammett relation, og(hyjko)= pa, has been applied for many years to substituent eifects on reaction kinetics in solution, and has been particularly successful for reactions of benzene compounds. Attempts have also been made to apply Hammett correlations to other phenomena such as infrared (T. L. Brown, 1960), ultraviolet (Jaffe and Orchin, 1962a) and nuclear magnetic resonance absorption frequencies (Bothner-By and Glick, 1956). 

On the base of work by Gordy and Stanford, the spectroscopic criterion, related to the extent of the shift to lower frequencies of the OD infrared absorption of deuterated methanol, was selected. It provides a measure of the hydrogen-bonding acceptor power of a sol-vent. The spectrum of a deuterated methanol solution in the test solution was compared with that of a solution in benzene and the hydrogen-bonding parameter was defined as... 

Hexaethoxycyclotriphosphazatriene is a colorless, odorless liquid for which n is 1.4522. The compound is soluble in petroleum ether, benzene, diethyl ether, carbon tetrachloride, or chloroform, but almost insoluble in water. The frequencies of the principal absorption maxima in the infrared spectrum are 3000, 1225, 1170, 1036, 972, 899, 813, 800, and 751 cm. The frequency at 1225 cm. is characteristic of a six-membered ring in this case. 

Another way of comparing low-frequency Raman and far-IR data is to compare the absorption coefficient a(P) with the Raman spectrum in the R(P representation. Examples are shown in Fig. 3 for benzene and hexafluorobenzene [14,15]. The approximate expression, Ra(P) in Eq. (2) was used. Both molecules do not posses permanent molecular dipole moments, so the infrared spectrum is caused solely by induced dipole moments. Accordingly, the band shapes for the absorption coefficient and the R(P) representation are very similar [5]. When a permanent molecular dipole moment is present, the librational motion of this will give the main contribution to the far-IR intensity, whereas the intensity in the low-frequency Raman spectrum is determined by the anisotropy of the static molecular polarizability. In this case, it should be taken into account that the band shape in IR... 

Examples of these infrared bands are seen in Fig. 8.7. The first two rows of spectra illustrate benzene rings with alkane substituents. For these, the adjacent hydrogen wag bands tend to increase in frequency somewhat as the a carbon of the substituent is more highly substituted. We can note absorptions for toluene at 728 cm ethylbenzene at 745 cm isopropylbenzene at 759 cm and /ert-butylbenzene at 763 cm ... 

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