Infrared mechanical coupling

The band positions associated with the various vibrations are primarily dependent on mass- and force-constant effects. They are sensitive to small, but highly specific perturbations, induced by effect of stereo chemistry, mechanical coupling, intramolecular electrical effects, and intermolecular interaction. Thus, the physical state of the compound, liquid, amorphous solid, crystalline solid (including polymorphism) may alter the frequency of absorption. When using band-by-band correlation with a standard compound for identification of an unknown, these factors should be considered. More detailed information appears in the textbooks on infrared spectroscopy (48-53). 

An infrared (IR) spectrum of MA is shown in Fig. 1-5. The most characteristic anhydride bands appear at -- 1780 and 1850 cm The exact position of these bands is slightly dependent on the nature of the sample as well as the solvent used. This doublet is usually ascribed to mechanical coupling of carbonyl vibrations. Thus, the high-frequency band is produced by the symmetric (in-phase) stretching mode whereas the low-frequency band is produced by the asymmetric (out-of-phase) mode. The 1780-cm band is very strong and can be conveniently used to estimate the amount of MA in a mixture by quantitative IR ( 1%). The method is quite useful when solutions are examined by IR. In solutions such as chloroform, benzene, etc., MA has been studied in detail and assignments have been made. In the presence of other anhydrides,particularly polyesters,this could be a valuable method. Of course, all standard methods and limitations of quantitative IR determination apply. Infrared spectra of gaseous MA and Raman spectra are also reported. 

The eigenvalue problem was introduced in Section 7.3, where its importance in quantum mechanics was stressed. It arises also in many classical applications involving coupled oscillators. The matrix treatment of the vibrations of polyatomic molecules provides the quantitative basis for the interpretation of their infrared and Raman spectra. This problem will be addressed tridre specifically in Chapter 9. 

Kinetic measurements of the ring-opening polymerization of trimethylene carbonate (TMC) versus the enchainment of oxetane and CO2 to provide poly (TMC) reveal that these processes in the presence of (salen)CrCl and an ammonium salt have similar free energies of activation (AG ) at 110°C. This similarity in reactivity coupled with the observation that in situ infrared studies of the copolymerization of oxetane and CO2 showed the presence of TMC during the early stages of the reaction has led to the overall mechanism for copolymer production shown in... 

The flame retardant mechanism of PC/ABS compositions using bisphenol A bis(diphenyl phosphate) (BDP) and zinc borate have been investigated (54). BDP affects the decomposition of PC/ABS and acts as a flame retardant in both the gas and the condensed phase. The pyrolysis was studied by thermogravimetry coupled with fourier transform infrared spectroscopy (FUR) and nuclear magnetic-resonance spectroscopy. Zinc borate effects an additional hydrolysis of the PC and contributes to a borate network on the residue. 

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