Commercially-available dicyclohexano-18-crown-6 (DC18C6) is a mixture of two easily-resolved isomers, cis-syn-cis and cis-anti-cis, differing in whether the cyclohexyl rings are linked to the main macroring with both substituents on-the same side or on opposite sides, respectively. We have investigated the reactions of DC18C6 and its alkali metal ion complexes in a solvent-free, gas-phase environment. Both isomers have greater free energies of alkali cation attachment in the gas phase than unsubstituted 18-crown-6 (18C6), with the greatest differences between the substituted and unsubstituted ligands (>10 kJ mol(-1)) occurring for the smallest metal ions. This is rationalized in terms of the greater polarizability of DC18C6. Comparison with solution data indicates there must be a greater cost in free energy for desolvating the cavity of DC18C6 than for 18C6. The efficiency of metal transfer from 18C6 to DC18C6 is high (greater than or equal to 20% for all alkali metal ions with either isomer) and increases with decreasing alkali ion size, Li+ being nearly a factor of 3 faster than Cs+ for the anti isomer. The variation in rates with cation size can be explained on the basis of decreasing barrier height on the potential energy surface for cation transfer as the depths of the wells for metal binding increase. The syn and anti isomers differ measurably in free energy of cation attachment, in kinetics of cation uptake from 18C6-alkali metal complexes, and in the rates at which 2:1 ligand-metal complexes form. The latter for both isomers are slower than for unsubstituted 18C6, reflecting greater steric hindrance in the substituted crown.