Issue 1, 2013

Atropisomerization of di-para-substituted propyl-bridged biphenyl cyclophanes

Abstract

The influence of electron donors and electron acceptors of variable strength in the 4 and 4′ position of 2 and 2′ propyl-bridged axial chiral biphenyl cyclophanes on their atropisomerization process was studied. Estimated free energies ΔG(T) of the rotation around the central biphenyl bond which were obtained from 1H-NMR coalescence measurements were correlated to the Hammett parameters σp as a measure for electron donor and acceptor strength. It is demonstrated that the resulting nice linear correlation is mainly based on the influence of the different substituents on the π-system of the biphenyl cyclophanes. By lineshape analysis the rate constants were calculated and by the use of the Eyring equation the enthalpic and entropic contributions were evaluated. Density functional theory calculations show a planar transition state of the isomerization process and the calculated energy barriers based on this reaction mechanism are in good agreement with the experimentally obtained free energies.

Graphical abstract: Atropisomerization of di-para-substituted propyl-bridged biphenyl cyclophanes

Supplementary files

Article information

Article type
Paper
Submitted
29 Jun 2012
Accepted
21 Sep 2012
First published
24 Sep 2012

Org. Biomol. Chem., 2013,11, 110-118

Atropisomerization of di-para-substituted propyl-bridged biphenyl cyclophanes

J. Rotzler, H. Gsellinger, A. Bihlmeier, M. Gantenbein, D. Vonlanthen, D. Häussinger, W. Klopper and M. Mayor, Org. Biomol. Chem., 2013, 11, 110 DOI: 10.1039/C2OB26243F

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