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-substituentsI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
