The use of chemical shifts <Emphasis Type="Italic">vs.</Emphasis> coupling constants for studying tautomerism: a combined experimental and theoretical approach |
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| Authors: | Dionisia Sanz Rosa M Claramunt Ibon Alkorta José Elguero |
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| Institution: | (1) Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, Universidad Nacional de Educación a Distancia (UNED), Senda del Rey 9, 28040 Madrid, Spain;(2) Instituto de Química Médica, Consejo Superior de Investigaciones Científicas (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain |
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| Abstract: | When observing average NMR signals originated from a rapid equilibrium, the procedure to estimate the composition of the mixture
is to use interpolation. To illustrate the difficulties of this approach, the much-studied case of the NH and OH tautomers
of pyrazolinones will be reexamined. Calculated absolute shieldings and coupling constants were compared with experimental
data. Although the large predominance of the OH tautomer in DMSO was confirmed, the result is a little disappointing because
no consistency in the percentages was achieved using chemical shifts and coupling constants. |
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| Keywords: | 13C NMR 15N NMR CP/MAS GIAO Coupling constants Tautomerism |
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