HYDROGEN-BONDING IN N-SUBSTITUTED AMINO-ACIDS - CRYSTAL-STRUCTURE OF THE N,N-DIETHYL-BETA-ALANINE-BENZENE INCLUSION COMPOUND

Supersaturated solutions of N, N-diethyl-β-alanine (NNDEBA) in benzene deposit orthorhombic crystals, space group Pbcm, having four molecules of NNDEBA and four molecules of benzene in a unit cell with dimensions (160 K) a = 5.491 (1), b = 13.426 (3), c = 1 7.766 (6) Å. The amino acid molecules form hydrogen-bonded chains of zwitterions parallel to the b axis of the crystal. The molecules are situated on a crystallographic mirror plane, but the hydrogen-bonded oxygen appears to undergo large amplitude motion, so that the oxygen is ±0.46 A out of the mirror plane most of the time. This motion leads to a mean N-O distance of 2.66 (2) Å. The in-plane N-O distance is computed to be 2.594 (5) Å. The zwitterion chains stack to form sheets parallel to the ab plane, with the ethy;l groups nearly perpendicular to the sheets. Such a packing forms channels in which the benzene molecules are found. Electrostatic calculations in the point dipole approximation show that dipole-dipole interactions greatly stabilize an ab plane, but do not contribute significantly to the binding between adjacent ab planes. © 1979, American Chemical Society. All rights reserved.