Enantiomerically Pure Quaternary Ammonium Salts with a Chiral Alkyl Chain N(CH3)(n-C3H7)2(sec-C4H9)I: Synthesis and Physical Studies

A pair of enantiomerically pure quaternary ammonium salts with a chiral side chain, methyl-(R)-(1-methylpropyl)di(n-propyl) ammonium iodide I and methyl-(S)(1-methylpropyl) di (n-propyl) ammonium iodide 2, and the related racemate, methyl-(rac)-(1-methylpropyl) di (n-propyl) ammonium iodide 3, were synthesized through a reductive alkylation procedure, starting from enantiomerically pure and, also, racemic forms of (rac)-(I-methylpropyl)amine. A spectroscopic chiroptical signature in solution was provided by the Raman optical activity spectra of compounds 1 and 2. The crystallographic structures of 1, 2, and 3 were examined by single crystal X-ray diffraction. 1 crystallizes in the tetragonal space group P4(3)2(1)2 (no. 96), a = b = 12.826 (2) angstrom, c = 17.730 (2) angstrom, v = 2916.9 (5) angstrom(3), Z = 8, Flack coefficient 0.04 (2). 2 crystallizes in the tetragonal space group P4(1)2(1)2 (no. 92), a = b = 12.842 (1) angstrom, c = 17.749 (2) angstrom, V = 2927.0 (5) angstrom(3), Z = 8, Flack coefficient 0.05 (2). The crystal structures and space groups for 1 and 2 are enantiomorphs and the crystallographic investigation confirmed the absolute configuration of the stereocenter in both compounds. 3 crystallizes in the monoclinic space group P2(1)/n(no. 14), a = 8.178 (1) angstrom, b = 14.309 (2) angstrom, c = 12.328 (2) angstrom, beta = 96.811 (6)degrees, V = 1432.4 (2) angstrom(3), Z=4.Chirality 20:1085-1091,2008. (C) 2008 Wiley-Liss, Inc.