SOLUTION-STATE CONFORMATIONAL HOMOGENEITY IN 8-MEMBERED RINGS CONTAINING VICINAL LONE-PAIRS OF ELECTRONS

-6-phenyl-3,4-dihydro-2H,6H-1,5,4-benzodioxazocine (1) gives crystals belonging to the monoclinic space group P2(1)/n, and at 293 K: a = 13. 309(1), b = 6.1615(6), c = 16.753(1) Angstrom, beta = 100.522(5)degree s, V = 1350.6(2) Angstrom(3), Z = 4, R(F) = 0.045, and R(w)(F) = 0.049 . The solid-state structure was found to be a twist-chair-flattened ch air conformation (TCfC) in which the benzo ring is located in the flat tened-chair portion of the molecule, the N-methyl group occupies and e quatorial orientation vis-a-vis the -(C) under bar H-2 (C) under bar H 2N- fragment, and the phenyl ring resides in an exo quasi-equatorial p osition relative to the -(C) under bar H(Ph)-O-N- fragment. The magnit udes of the H-1 NMR vicinal coupling constants in the -OCH2CH2NO- frag ment are consistent with the same TCfC conformation and N-configuratio n as found in the crystal in which the vicinal nitrogen lone pair (LP) of electrons is as far away from each of the two oxygen lone pairs as possible (two anticlinal LP-N-O-LP arrangements minimize unfavorable electrostatic interactions).