Dynamic NMR Analysis of Conformational Isomerism in a Diterpenoid Carboxamide

✍ Scribed by Richard C. Cambie; Michael J. Taylor; Peter S. Rutledge; Ralph J. Stevenson; Paul D. Woodgate

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 367 KB
• Volume: 34
• Category: Article
• ISSN: 0749-1581
• DOI: 10.1002/(sici)1097-458x(199605)34:5<360::aid-omr887>3.0.co;2-4

✦ Synopsis

Conformational changes in N,N-diethyl-14-hydroxy-l2,19-dimethoxypodocarpa-8,11,13-triene-l3-carboxamide were studied by variable-temperature 'H and I3C NMR over the range 228-328 K using three hydrogen and six carbon indicator sites. The parameters A H * = 48.7 f 2.0 kJ mol-l, AS* = -23 f 7 J K mol-' and AG&,, = 55.6 f 4.3 kJ mol-' were obtained, which were attributed to restricted rotation of the C-CONEt, bond. Restricted C-N rotation was also detected for which the free energy of activation at 250 K was eu. 53 kJ mol-'. Hydrogen bonding of the carboxamide to the adjacent hydroxy group can account for the low value of the C-N activation energy.