AbstractReactions of Cu2with several small molecules have been studied in the gas phase, under thermalized conditions at room temperature, in a fast‐flow reactor. They fall into one of two categories. Cu2does not react with O2, N2O, N2, H2, and CH4at pressures up to 6 torr. This implies bimolecular rate constants of less than 5 × 10−15cm3s−1at 6 torr He. Cu2reacts with CO, NH3, C2H4, and C3H6in a manner characteristic of association reactions. Second‐order rate constants for all four of these reagents are dependent on total pressure. The reactions with CO, NH3, and C2H4are in their low pressure limit at up to 6 torr He buffer gas pressure. The reaction with C3H6begins to show fall‐off behavior at pressures above 3 torr. Limiting low‐pressure, third‐order rate constants are 0.66 ± 0.10, 8.8 ± 1.2, 9.3 ± 1.4, and 85 ± 15 × 10−30cm6s−1in He for CO, NH3, C2H4, and C3H6, respectively. Modeling studies of these rate constants imply that the association complexes are bound by at least 20 kcal mol−1in the case of C2H4and C3H6and at least 25 kcal mol−1in the other cases. The implications of these results for Cu‐ligand bonding are developed in comparison with existing work on the interactions of these ligands with Cu atoms, larger clusters, and surfaces