Journal
CHEMISTRY-A EUROPEAN JOURNAL
Volume 15, Issue 11, Pages 2645-2652Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/chem.200801963
Keywords
biphenyls; density functional calculations; NMR spectroscopy; steric effects
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Funding
- Universities of Perugia and Bologna
- Ministero dell'Istruzione
- Universita' e Ricerca [2004033322, 2005035330]
- Schweizerische Nationalfonds zur Forderung der wissenschaftlichen Forschung, Bern [20100'336-02]
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Torsional barriers of 15 ortho-substituted biphenyls have been determined computationally using the B3LYP density functional and experimentally by variable-temperature (dynamic) nuclear magnetic resonance. Taking advantage of the 3'-isopropyldimethylsilyl group as a novel and superior diastercotopicity probe and tracking coalescence temperatures down to -173 degrees C (100 K), activation energies of aryl-aryl rotation as small as 5 kcal mol(-1) can be assessed. The 2-X/2'-H repulsion increments thus derived are powerful parameters for rationalizing and predicting the conformational behavior of aromatic compounds carrying ortho substituents.
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