The electronic structures and energies of (H2O)(n) . CCH and (H2O)(n) . HCC complexes (n = 1-3) between CCH and water have been theoretically investigated at the UB3LY-P/6-311++G(2df,p)//UB3LYP/6-311G(d,p) level. The complexes with n = 2-3 are cyclic structures with homodromic hydrogen-bond chain. The (H2O)(n) . CCH (n = 1-3) complexes show increasing stabilities towards CCH- or H2O-eliminations of 2.3, 5.8 and 7.6 kcal/mol and are energetically more stable than the corresponding (H2O)(n) . HCC complexes by 0.8, 2.7 and 3.4 kcal/mol, respectively, due to the charge-separation-enhanced hydrogen bonds within (H2O)(n) . CCH (n = 2,3). Strong interactions between CCH and (H2O)(2) and (H2O)(3) clusters suggest special solvent effects of water on the chemical behavior of unsaturated radicals. (C) 2002 Elsevier Science B.V. All rights reserved.