Rotational Energy Barrier around the C1–C11 Single Bond in Lamellarins: A Study by Variable-Temperature NMR
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In order to estimate the free energy barrier to rotation around the C1-C11 single bond in lamellarins, new lamellarin analogues (1a), (1b), (2a), and (2b) possessing diastereotopic protons or carbons at the C1 aryl moiety were synthesized. Variable-temperature 1H and 13C NMR measurements of these analogues revealed that the free energy barriers to rotation around the C1-C11 axis in 5,6-saturated and 5,6-unsaturated lamellarins were around 72-74 and 83-87 kJ/mol, respectively.
HETEROCYCLES 88(2), 1121-1133, 2014