The self-complementary (Z)-configured U*[c e ]A ( * ) dinucleotide analogues 6, 8, 10, 12, 14, and 16, and the A*[c e ]U ( * ) dimers 19, 21, 23, 25, 27, and 29 were prepared by partial hydrogenation of the corresponding ethynylene linked dimers. Photolysis of 14 led to the (E)-alkene 17. These dinucleotide analogues associate in CDCl 3 solution, as evidenced by NMR and CD spectroscopy. The thermodynamic parameters of the duplexation were determined by vant Hoff analysis. The (Z)-configured U*[c e ]A ( * ) dimers 14 and 16 form cyclic duplexes connected by Watson -Crick H-bonds, the (E)-configured U*[c e ]A dimer 17 forms linear duplexes, and the U*[c e ]A ( * ) allyl alcohols 6, 8, 10, and 12 form mixtures of linear and cyclic duplexes. The C(6/I)-unsubstituted A*[c e ]U allyl alcohols 19 and 23 form linear duplexes, whereas the C(6/I)-substituted A*[c e ]U* allyl alcohols 21 and 25, and the C(5'/I)-deoxy A*[c e ]U ( * ) dimers 27 and 29 also form minor amounts of cyclic duplexes. The influence of intra-and intermolecular H-bonding of the allyl alcohols and the influence of the base sequence upon the formation of cyclic duplexes are discussed.