Accurate 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 diastereotopicity probe and tracking coalescence temperatures down to –173 °C (100 K), activation energies of aryl-aryl rotation as small as 5 kcal/mol 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

B-Values as a Sensitive Measure of Steric Effects

LUNAZZI, LODOVICO;MAZZANTI, ANDREA;
2009

Abstract

Accurate 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 diastereotopicity probe and tracking coalescence temperatures down to –173 °C (100 K), activation energies of aryl-aryl rotation as small as 5 kcal/mol 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
CHEMISTRY-A EUROPEAN JOURNAL
R. Ruzziconi; S. Spizzichino; L. Lunazzi; A. Mazzanti; M. Schlosser
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11585/82953
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