8] Crystal structure analysis of 6 : monoclinic. P2,/a, a = 17.919(18). b = 16.238(16), c = 34.53(3) A, j3 = 90.83(6)", V = 10047 A3, Z = 8; 7501 reflections (I> 2 4 four-circle diffractometer, Mo,, radiation, w scan), R = 0.065, R, = 0.059 (As, Si, 0, C anisotropic, H in calculated positions, isotropic temperature factors, phenyl rings as rigid groups, 921 parameters).'"' [9] The arsaalkenes 8 and 9 were characterized by 'H NMR as well as " C NMR spectroscopy and also mass spectrometry. The 1,3,2,4-dioxadisilethane 7 [a(' %) = -6.38; MS (EI, 70 eV): m/z 900 ( M i , 84(%), 435(Is,SiH+, IOO)] is identical with the product from the oxidation of

The energies of complexation of methyl (R)/(S)‐2‐chloropropionate [(R)/(S)‐2] with heptakis(3‐O‐acetyl‐2,6‐di‐O‐pentyl)‐β‐cyclodextrin (1) and the structures of the corresponding complexes were determined by molecular‐dynamcis (MD) simulations at 300 and 333 K. The geometry of the complexes, the conformations of complexed and uncomplexed 1 and (R)/(S)‐2 and the closest H–H distances between host and guest in the complexes were determined from the trajectories. The results correspond to the experimental findings from enantioselective gas chromatography.

Übereinstimmend folgt die größere Stabilität des Komplexes aus (S)‐2‐Chlorpropionsäuremethylester (S1 und dem hydrophoben Cyclodextrinderivat 2 aus gaschromatographischen und NMR‐spektroskopischen Studien sowie aus Moleküldynamiksimulationen der Systeme (RS)‐1/2, R)‐1/2 und (S‐1/2. Die 1H‐NMR‐Signale des (S‐Enantiomers werden durch die Komplexierung um bis zu δσ = 0.5 gegenüber denen des (R)‐Enantiomers tieffeldverschoben, d.h. Cyclodextrine können somit nicht nur für Enantiomerentrennungen, sondern auch als chirale Verschiebungsreagentien verwendet werden. R2 = R6 = η‐Pentyl, R3 = Acetyl.

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