A conformational study on the 1-butyl-3-methylimidazolium chloride (bmimCl) is presented to test the influence of the conformers in the estimation of physicochemical properties. Twenty starting structures were proposed, and 12 different conformers were obtained after geometry optimization at DFT (BVP86/TZVP/DGA1) level. COnductor-like Screening MOdel (COSMO) methodology was applied to estimate their properties in the liquid phase. Sigma-profiles and sigma-potentials were computed for the conformers that are most ionic, least ionic, and energetically most stable. COSMO-Real Solvents method was used to test predictions of boiling point, density, and viscosity for these individual conformers and for a statistical mixture of conformers. © 2012 Wiley Periodicals, Inc.