Four substituted simple alkanes - 1-bromo-2-chloroethane, 1-chloropropane, 1,1-dichloropropane, and 1,1,2-trichlorotrifluoroethane - can exist in gauche positive (G), gauche negative (G'), and trans (T) conformers. The G and G' conformers are optical rotamers, while the T conformer is achiral. Here, the first observation of the preferential population of the optical rotamers in these alkanes induced by the molecular flow through molecular drag pumps is reported. The molecular mechanism of the observed enantiomeric excess of the studied alkanes is rationalized in the general framework of the molecular chirality generated through oriented collisions involving flowing molecules in macroscopic translation-rotational motions induced by a rotating surface. (C) 2011 Elsevier B.V. All rights reserved.