Ortho-substituted para-terphenyl hydrocarbons exist as trans and cis atropisomers that have been identified by low temperature NMR spectroscopy. The interconversion barriers increase with the increasing dimensions of the ortho-substituents R, (R = Me, Et, i-Pr, t-Bu in compounds 1-4, respectively), the experimental values being matched by ab-initio calculations. Single crystal X-ray diffraction of compounds 1 (R =Me) and 4 (R = t-Bu) shows that only the trans atropisomer is present in the solid state. Low temperature NMR spectra of derivative 4, obtained in non equilibrium conditions, indicate that the cis is more populated than the trans atropisomer in solution, favored, it is suggested, by attractive interactions between the alkyl groups.
L. Lunazzi, A. Mazzanti, M. Minzoni, J. E. Anderson (2005). Structure, Conformation and Dynamic Processes of the Stereolabile Atropisomers of Hindered Terphenyl Hydrocarbons. ORGANIC LETTERS, 7, 1291-1294 [10.1021/ol050091a].
Structure, Conformation and Dynamic Processes of the Stereolabile Atropisomers of Hindered Terphenyl Hydrocarbons
LUNAZZI, LODOVICO;MAZZANTI, ANDREA;MINZONI, MIRKO;
2005
Abstract
Ortho-substituted para-terphenyl hydrocarbons exist as trans and cis atropisomers that have been identified by low temperature NMR spectroscopy. The interconversion barriers increase with the increasing dimensions of the ortho-substituents R, (R = Me, Et, i-Pr, t-Bu in compounds 1-4, respectively), the experimental values being matched by ab-initio calculations. Single crystal X-ray diffraction of compounds 1 (R =Me) and 4 (R = t-Bu) shows that only the trans atropisomer is present in the solid state. Low temperature NMR spectra of derivative 4, obtained in non equilibrium conditions, indicate that the cis is more populated than the trans atropisomer in solution, favored, it is suggested, by attractive interactions between the alkyl groups.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
