Off-center oxygen-arene interactions in solution: a quantitative study

reaction: see text] Triptycenes with C1-MeO/RCOO (R = H, Me, Et, i-Pr, CF3) and C9-XC6H4CH2 (X = Me, H, F, CN, CF3) have been prepared to determine lone pair-arene interactions in the off-center configuration. The ratios of the syn and anti conformers were determined by low-temperature NMR spectroscopy. The syn conformer allows the attached arene and the MeO/ester to interact with each other while the anti conformer does not. The free energies of interaction have been derived from the syn/anti ratios. Compound 7 in the ester series with X = H and R = CF3 is the only compound that shows a slightly repulsive interaction (0.08 kcal/mol). Compound 2e in the MeO series with X = CF3 exhibits an attractive interaction (-0.47 +/- 0.05 kcal mol). All other compounds show smaller attractive interactions.