The chloride of the decyl ester of L-proline has been used as a chiral dopant where the achiral host detergent was tetradecyltrimethylammonium bromide. The twist and the sense of the helix were measured as a function of the chiral dopant concentration, using the fingerprint texture and Grandjean planes observed under a polarizing microscope. The magnitude of the twist as a function of the chiral dopant concentration initially rose and fell, while the sense of helix was positive. At about 10% the twist magnitude passed through zero, and then with increasing amounts of the chiral dopant the sense of the helix became negative. This inversion in the twist sense is thought to be due to a concentration-dependent distribution of the cis and trans molecular rotamers derived from rotation around the >CH-CO2- bond. The existence of cis and trans rotamers is confirmed using C-13 NMR.