Different spectra: structural data obtainable

Many different spectroscopy techniques can be used to provide stmctural information concerning polymers. In terms of vibrational spectroscopy, Strobl and Hagedom (1978) showed how the Raman spectrum of polyethylene could be considered in terms of characteristic bands associated with the crystalline phase, a melt-like amorphous phase and a disordered phase of anisotropic nature. Comparison of structural data obtained in this way with equivalent measures obtained by densitometry and X-ray scattering revealed agreement. Similar approaches have... 

The precise geometrical data obtained by microwave spectroscopy allow conclusions regarding bond delocalization and hence aromaticity. For example, the microwave spectrum of thiazole has shown that the structure is very close to the average of the structures of thiophene and 1,3,4-thiadiazole, which indicates a similar trend in aromaticity. However, different methods have frequently given inconsistent results. 

Denaturation. The stability of LADH and its denaturation has been studied under a variety of conditions including acid pH, and different concentrations of urea and guanidine hydrochloride. At pH 5, LADH loses its activity while still in the dimeric state, and at lower pH dissociation occurs, as can be seen in the drastic change in the fluorescence polarization spectrum.1410 The spectral data obtained are consistent with unfolding of the tertiary structure, some of which occurs before subunit dissociation. 

Nuclei that are typically analyzed with this technique include those of 13C, 31P, 1SN, 2SMg, and 23Na. Different crystal structures of a compound can result in perturbation of the chemical environment of each nucleus, resulting in a unique spectrum for each form. Once resonances have been assigned to specific atoms of the molecule, information on the nature of the polymorphic variations can be obtained. This can be useful early in drug development, when the single-crystal structure may not be available. Long data acquisition times are common with solid-state NMR, so it is often not considered for routine analysis of samples. However, it is usually a very sensitive technique, and sample preparation is minimal. NMR spectroscopy can be used either qualitatively or quantitatively, and can provide structural data, such as the identity of solvents bound in a crystal. 

Compound (95) showed a molecular formula of C60H82O8, also by HRFAB-MS and its 13C-NMR spectrum. The main difference with (94) was the absence of the C-6 -C-7 double bond, confirmed by 2D NMR spectroscopy. The absolute configuration was determined-as in the former case-by analysis of its CD spectrum. According to the data obtained, the structure of (95) was assigned as 6 ,7 -dihydro-scutionin aB, Fig. (51). 

Compound (98) showed a molecular formula of C90H122O12, according with its FAB-MS and 13C-NMR spectra. Analysis of the data obtained from the H-NMR spectrum and the 2D NMR experiments, showed that (98) was an isomer of (97), with different substitution of the subunits. Its absolute configuration was determined by its CD curve. The lingkages between the units were determined to be C3-0-C2 , C4-0-C3 and C6 -0-C2 , C7 -0-C3 , respectively. According to the data obtained, the structure of (98) is showed below, and the compound was called triscutin B, Fig. (54). 

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