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Paper
Org. Biomol. Chem., 2009, 7, 5156 - 5162, DOI: 10.1039/b916021n
Topically resolved intramolecular CH-
interactions in phenylalanine derivativesW. Brian Jennings, Noel J. P. McCarthy, Padraig Kelly and John F. Malone
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-
interactions shifted well upfield (
5.4–5.8 at -88 °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).
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