Dynamic NMR Analysis of Conformational Isomerism in a Diterpenoid Carboxamide

Autor:	Paul D. Woodgate, Richard C. Cambie, Ralph J. Stevenson, Peter S. Rutledge, Michael J. Taylor
Rok vydání:	1996
Předmět:	Hydrogen Hydrogen bond medicine.drug_class Stereochemistry chemistry.chemical_element Carboxamide General Chemistry Activation energy Carbon-13 NMR Terpenoid chemistry medicine General Materials Science Carbon Conformational isomerism
Zdroj:	Magnetic Resonance in Chemistry. 34:360-364
ISSN:	1097-458X 0749-1581
DOI:	10.1002/(sici)1097-458x(199605)34:5<360::aid-omr887>3.0.co;2-4
Popis:	Conformational changes in N,N-diethyl-14-hydroxy-12,19-dimethoxypodocarpa-8,11,13-triene-13-carboxamide were studied by variable-temperature 1H and 13C NMR over the range 228–328 K using three hydrogen and six carbon indicator sites. The parameters ΔH≠ = 48.7±2.0 kJ mol−1, ΔS≠ = −23±7 J K mol−1 and ΔG298≠ = 55.6±4.3 kJ mol−1 were obtained, which were attributed to restricted rotation of the C-CONEt2 bond. Restricted C—N rotation was also detected for which the free energy of activation at 250 K was ca. 53 kJ mol−1. Hydrogen bonding of the carboxamide to the adjacent hydroxy group can account for the low value of the C—N activation energy.
Databáze:	OpenAIRE
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