Unprecedented detection of enantiomerization pi-barriers due to restricted aryl torsion: case of 1,8-di-arylbiphenylenes.
Dynamic NMR spectroscopy allowed, for the first time, the determination of the pi-barriers responsible for the enantiomerization processes in derivatives bearing two aryl substituents bonded to a planar framework: this could be achieved in the case of 1,8-di-m-tolylbiphenylene (1) and 1,8-di-m-xylylbiphenylene (2). In derivative 1, the three possible conformers predicted by DFT computations (anti-in, syn, and anti-out) were detected, and in addition, the steric barrier responsible for their interconversion could be measured. The barriers predicted by DFT calculations were found in satisfactory agreement with experimental data.
Lunazzi
Lodovico
L
Department of Organic Chemistry "A. Mangini", University of Bologna, Viale, Risorgimento 4, Bologna 40136, Italy.
Mancinelli
Michele
M
Mazzanti
Andrea
A