1H and 13C NMR study of substituted 3-OH pyridines
nJHH, nJCH and δ13C values have been measured for a series of X substituted 3-hydroxypyridines (X = 2-NH2, 2-NO2, 5-Cl, 6-CH3, 2-Cl, 2-Br, 2-I). The results show that the additivity of δ13C provides a valuable criterion to differentiate the phenolic from the zwitterion structure. This conclusion is...
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| Autores principales: | , |
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| Formato: | JOUR |
| Acceso en línea: | http://hdl.handle.net/20.500.12110/paper_00222860_v221_nC_p299_DeKowalewski |
| Aporte de: |
| Sumario: | nJHH, nJCH and δ13C values have been measured for a series of X substituted 3-hydroxypyridines (X = 2-NH2, 2-NO2, 5-Cl, 6-CH3, 2-Cl, 2-Br, 2-I). The results show that the additivity of δ13C provides a valuable criterion to differentiate the phenolic from the zwitterion structure. This conclusion is based on the fact that in the first case, for 2-NH2-, 2-NO2-, 5-Cl- and 6-CH3-3-hydroxypyridines, there is agreement between the experimental and the additivity δ13C values, while in the three halogen derivatives (2-Cl-, 2-Br- and 2-I-3-hydroxypyridines) the δexp-add C3 values of -4.95, -7.25 and 9.05 are probably due to the negative charge present on the three position of the zwitterion. Since the additivity of 1JCH values holds in all substances examined (unlike the case of the 2-pyridone derivatives) it is not possible to use that criterion to differentiate between the phenolic and dipolar structures. The above conclusions are in agreement with IR, pK, NQR, RX, kinetics experiments and quantum chemical calculations of other authors. © 1990. |
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