ISSN:
0030-4921
Keywords:
Chemistry
;
Analytical Chemistry and Spectroscopy
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
A new type of crown ethers containing a diphenyl ether unit has been prepared, the ring size ranging from 12 to 36. 1H and 13C NMR spectra of both free ligands and their metal-ion complexes have been recorded. For 18- and 21-membered compounds a general downfield shift was observed for both methylene and aromatic proton resonances on metal-ion complexation. The stoichiometry of K+ and Na+ complexes was deduced from chemical shift dependence on metal-ion concentration. The K+ and Na+ complexes of 18- and 21-membered rings have a guest to host ratio of 1:1, whereas the K+ salt of the 15-membered ring exists as a 1:2 complex in solution. The 1H shift observed on salt formation was attributed to electric-field and conformational effects. The 13C resonances for the aryl carbons, C-1, C-2 and C-3, and the α-methylene carbon in 15- and 18-membered rings were shifted upfield when an equivalent amount of KSCN was added in CDCI3-DMSO-d6. The shift changes were independent of the anion, and similar results were obtained for SCN-, Br-, and I- salts. The upfield shift is explained by conformational factors. The spectral changes were slight for 12- and 36-membered rings. In 15- and 18-membered rings, complexation induces conformational changes which force the C-α carbon into the plane of the benzene ring. The solution conformation of these molecules is discussed.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/mrc.1270120403
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