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Atropisomerization of di-para-substituted propyl-bridged biphenyl cyclophanes.
MedLine Citation:
PMID:  23059962     Owner:  NLM     Status:  Publisher    
Abstract/OtherAbstract:
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 (1)H-NMR coalescence measurements were correlated to the Hammett parameters σ(p) 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.
Authors:
Jürgen Rotzler; Heiko Gsellinger; Angela Bihlmeier; Markus Gantenbein; David Vonlanthen; Daniel Häussinger; Wim Klopper; Marcel Mayor
Publication Detail:
Type:  JOURNAL ARTICLE     Date:  2012-10-11
Journal Detail:
Title:  Organic & biomolecular chemistry     Volume:  -     ISSN:  1477-0539     ISO Abbreviation:  Org. Biomol. Chem.     Publication Date:  2012 Oct 
Date Detail:
Created Date:  2012-10-12     Completed Date:  -     Revised Date:  -    
Medline Journal Info:
Nlm Unique ID:  101154995     Medline TA:  Org Biomol Chem     Country:  -    
Other Details:
Languages:  ENG     Pagination:  -     Citation Subset:  -    
Affiliation:
Department of Chemistry, University of Basel, St. Johannsring 19, 4056 Basel, Switzerland. marcel.mayor@unibas.ch daniel.haeussinger@unibas.ch.
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