title: Topically resolved intramolecular CH-pi interactions in phenylalanine derivatives.
abstract: NMR spectra of imines and nitrones derived from benzophenone and phenylalanine or tyrosine show clear evidence of an aromatic edge-to-face interaction in solution. At low temperatures the two ortho protons of the edge interacting phenyl ring become topically resolved with the ortho proton NMR signal involved in the CH-pi interactions shifted well upfield (delta 5.4-5.8 at -88 degrees C) of the other ortho signal. Introduction of a para substituent into the phenylalanine ring has a modest effect on the upfield shift. The edge-to-face arrangement also manifests in the X-ray crystal structures of two of these compounds. Barriers to rotation around the syn phenyl-imino bond are also reported (10.5-11.1 kcal mol(-1)).
authors.affiliation: Department of Chemistry and Analytical & Biological Chemistry Research Facility, University College Cork, Cork, Ireland. brianj@ucc.ie
authors.forename: W Brian
authors.initials: WB
authors.lastname: Jennings
authors.forename: Noel J P
authors.initials: NJ
authors.lastname: McCarthy
authors.forename: Padraig
authors.initials: P
authors.lastname: Kelly
authors.forename: John F
authors.initials: JF
authors.lastname: Malone
mesh_terms: D001577:Benzophenones / Q000737:chemistry; D018360:Crystallography, X-Ray; D007097:Imines / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009589:Nitrogen Oxides / Q000737:chemistry; D010649:Phenylalanine / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D001577:Benzophenones; D007097:Imines; D009589:Nitrogen Oxides; C015388:nitrones; D010649:Phenylalanine; C047723:benzophenone