The current cryogenic distillation technology used for olefin-paraffin separation incurs extensive capital and operating costs. An alternative olefin-paraffin separation process, based on reactive absorption, could yield significant cost reductions. The research efforts described herein explored the structural characteristics of an NMP-CuCl-aniline absorption solution with ethylene to aid future development of olefin-paraffin separation systems. Solution IR and 1 H NMR spectroscopy suggested weak and labile Cu(I)-ethylene and Cu(I)-aniline coordination, which point to the coexistence of multiple structures in solution. Experiments also revealed solvent-dependent and temperature-dependent coordination. The agreement of the collected spectral data with literature implied single ethylene coordination, whereas the Cl À ion likely remained coordinated with Cu(I). Solvent interference prohibited detailed investigation of IR spectra, but 1 H NMR spectroscopy showed more promise as an analytical technique for the NMP-CuCl-aniline-ethylene system. Finally, a tradeoff appears to exist between ethylene capacity and complex stability, and thus, an optimal ligand must be found that balances these two competing needs.