The biphenyl-monitored effective size of unsaturated functional or fluorinated ortho substituentsReportar como inadecuado




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Published in: Organic & Biomolecular Chemistry, vol. 8, p. 4463-4471 Publication date: 2010

The size of a series of typical substituents has been probed by dynamic NMR measurements of the barriers to aryl-aryl rotation of the corresponding biphenyls. The resulting B values are meaningful because only mono-ortho substituted compounds were investigated and thus the results are not compromised by the non-additivity of multiple steric effects. On the basis of the chosen model system ethynyl and cyano groups were found to be slightly smaller than a phenyl ring. In contrast, vinyl and, in particular, formyl groups proved to be larger than phenyl. The latter difference is due to the loss of conjugation forces at the planar transition state. alpha-Hydroxyhexafluoroisopropyl is slightly more bulky than tert-butyl. Pentafluorophenyl and trifluoromethoxy exhibit nearly the same effective size as phenyl and methoxy, respectively Trifluoromethyl is somewhat smaller than isopropyl.

Keywords: Electron-Diffraction ; Internal-Rotation ; Conformational-Analysis ; Perdeuterated Biphenyl ; Molecular-Structure ; Torsional Barriers ; Gaseous State ; Density ; Stereodynamics ; Energy Reference EPFL-ARTICLE-172314doi:10.1039/c0ob00136hView record in Web of Science





Autor: Ruzziconi, Renzo; Spizzichino, Sara; Mazzanti, Andrea; Lunazzi, Lodovico; Schlosser, Manfred

Fuente: https://infoscience.epfl.ch/record/172314?ln=en







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