Another 15 pairs of diastereomeric 1 ,Zdisubstituted 1,2-diarylethanes have been separated by thin-layer chromatography on silica gel using solvent systems with and without secondary solvent effects. The results obtained, together with those from a previous study, indicate a correlation of RF+rylhro, > RFohreo) for 50 of the 52 diastereomeric pairs studied. Qualitative analysis by means of the Snyder's theory has been used to specify the scope and limitation of this correlation for diastereomers.of the type studied.
INTRODUCXON
In our first paper of this series1 we reported the correlation HFCergthro, > R fcllueo, obtained by thin-layer chromatography (TLC) on silica gel of 37 diastereomerit pairs of 1,2-clisubstituted 1,2-diarylethanes of the type 1. On the basis of general considerations, this result was attributed to two-point, and less sterically hindered, adsorption of only the fhreo-isomers. It was suggested that the correlation could be used for the assignment of the relative configurations of newly synthesized diastereomers of the type 1. At-CHcX)-CHIYI-Ar' X and Y = N&, , d-i, CqH or their derivatives 1 terythro and three) Ar and At-' P Ph or alkoxyphenyl CooperZ studied the TLC on silica gel of four c&tram pairs of compounds 2 and 3; in contrast to our study, a definite correlation was _ .-_> .
the related not found. This is not surprising as there is no reason to expect the same TLC separation order for diastereomers which differ in their molecular geometry as do 1, 2 and 3, and as do 2 and 3. Moreover the effective volumes of the strongly adsorbing groups are different, naxnel!l X and Y verms Ar and Xin these two studies. Subsequent papers have