CORRELATIONS OF STRUCTURE WITH BINDING ABILITY INVOLVING 9 HEMICARCERAND HOSTS AND 24 GUESTS

Hemicarcerands 1-9, composed by coupling through four O(CH2)(4)O or fo ur 1,3-(OCH2)(2)C6H4 bridging units in different pair combinations of three tetrol bowls (varying spanners, O(CH2)(n)O, n = 1, 2, or 3), hav e been examined for their abilities to incarcerate a variety of organi c guest compounds of widely differing structures. When the conformatio nally flexible tetrol bowl (spanners = O(CH2)(3)O) was coupled lip-to- lip to either of two rigid bowl units (spanners OCH2O or O(CH2)(2)O), the rigid units tended to impose their shapes on the mobile units in t he resulting hosts (H-1 NMR spectral and crystal structure evidence). Complexes were formed by heating to high temperatures host dissolved i n a large excess of guest. High structural recognition in complexation was observed for the 1,3-(OCH2)(2)C6H4-bridged hosts to favor binding of 1,2-disubstituted as compared to 1,3- and 1,4-disubstituted benzen es as guests. Three new crystal structures of hemicarceplexes identica l except for their spanner lengths are compared, and a fourth new stru cture allows comparison of identical hosts with different guests. Deco mplexation rates are compared in some cases. Interesting new kinds of restricted rotations of guests with respect to hosts were observed. Th ree examples of trace impurities in guests being scavenged by the host were encountered.