Stereodynamics and edge-to-face CH-pi aromatic interactions in o-phenethyl-substituted biaryls |
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Authors: | Jennings W Brian Farrell Brid M Malone John F |
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Institution: | Department of Chemistry and Analytical & Biological Chemistry Research Facility, University College Cork, Cork, Ireland. brianj@ucc.ie |
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Abstract: | As part of a search for systems that exhibit intramolecular aromatic edge-to-face interactions, a series of four biaryl compounds containing a phenethyl side chain were prepared. These compounds exist as a slowly interconverting mixture of two atropisomers due to steric hindrance to rotation about the biaryl bond. The more thermodynamically stable isomer exhibits an abnormal shielding of an ortho-proton in solution indicative of an edge-to-face CH-pi interaction with the terminal phenyl ring on the side chain. This tilted-T type of geometry was observed in the X-ray crystal structure of one of the compounds. The edge-to-face conformation in solution is estimated by variable temperature NMR studies to be energetically favored by ca. 1.6 kcal mol(-1) but entropically disfavored by ca. 5.0 cal K(-1) mol(-1). |
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