Electronic effects in polyarylvinyl propellers. Solid state structures and dynamic behaviour in solution of several crowded enol derivatives

Abstract

By means of dynamic NMR (DNMR) investigations the dynamic behaviour of several crowded enol derivatives 5–11 and of the enols 12 and 13 has been studied. The NMR data are in agreement with the presence of vinyl propeller structures in solution, which fits the results of X-ray structural analysis. As deduced from a comparison with electrochemical data for the compounds investigated a severe electronic influence of the residue R attached at the enol ether oxygen atom on the rotation barriers can be ruled out. For Mes₂CC(Ph)OR systems, two different kinds of dynamic processes have been deduced on the basis of the DNMR data: first, an isolated rotation of the phenyl ring with a low activation barrier and, secondly, a correlated rotation of the two β-mesityl rings with a substantially higher barrier.