Stereodynamics and edge-to-face CH-pi aromatic interactions in o-phenethyl-substituted biaryls.
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).
Jennings
W Brian
WB
Department of Chemistry and Analytical & Biological Chemistry Research Facility, University College Cork, Cork, Ireland. brianj@ucc.ie
Farrell
Brid M
BM
Malone
John F
JF
D001643:Bridged Bicyclo Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008958:Models, Molecular; D008968:Molecular Conformation; D012680:Sensitivity and Specificity; D013237:Stereoisomerism; D013696:Temperature; D013816:Thermodynamics
D001643:Bridged Bicyclo Compounds