ISSN:
0377-0486
Schlagwort(e):
Chemistry
;
Analytical Chemistry and Spectroscopy
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
Raman spectra of styrene (S), 3-fluorostyrene (3FS), 3-chlorostyrene (3CS) and 3-methylstyrene (3MS) and their complexes in α-, β- and γ-cyclodextrins (α-, β-, γCD) were recorded at various temperatures. The substituted styrene molecules were found to provide good group frequencies, namely, vC=C and vC—H, for probing the guest molecules. Generally, the C=C oscillator is shown to be a good probe for studying conformational equilibria of the guest molecule perturbed by complex formation with the various CD molecules. The CH oscillators provide information concerning plausible structures for the complexes. On the whole, all the spectral observations are consistent with different types of structures for the (S, 3MS)-αCD and (3FS, 3CS)-αCD complexes. In particular, the Raman spectroscopic results suggest that, for 3MS-αCD the vinyl group keeps some rotational freedom. For 3FS-αCD and 3CS-αCD, it is suggested that the most electronegative fluorine and chlorine atoms are left outside the the CD cavity, with the vinyl group rotationally hindered. For the γCD complexes, the wider CD cavity sould be able to accommodate all the guest molecules considered keeping the conformer distributions of the pure liquids approximately. However, the inclusion process seems to hinder the internal rotation in such a way that even below 200 K the conformer distribution remains similar to that of the pure liquid at room temperature.
Zusätzliches Material:
7 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/jrs.1250250721
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