13C NMR STUDY OF SUBSTITUENT EFFECTS IN 1,2,4-OXADIAZOLE AND 1,2,4-THIADIAZOLE DERIVATIVES |
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Authors: | Hıkmet Ağirbaş Yeşim Kara |
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Institution: | Kocaeli University , Izmit, Turkey |
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Abstract: | 13C chemical shifts of C═N, C═O and C═S carbons of 3,4-disubstituted-1,2,4-oxadiazole-5-ones(thiones) and 3,4-disubstituted-1,2,4-thiadiazole-5-ones have been determined in CDCl3 solution. Exceptionally good Hammett correlations of 13C NMR chemical shifts of these carbons with σ were obtained. The negative ρ values observed (inverse substituent effects) indicate π-polarization of the C═N, C═O and C═S bonds. As expected, the long distance C═O and C═S 13C chemical shifts were found less susceptible to substituent-induced electronic changes. |
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Keywords: | 1 2 4-oxadiazole-5-ones(thiones) 1 2 4-thiadiazole-5-ones 13C NMR substituent effects |
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