the probe enantiomers and the chiral
substrate, a slight ee is created in both the solution and in the vapor phase. The apparatus transports the vapor away from the solution via N carrier gas such that equilibrium is not reached, and the ee can grow larger. The vapor is then condensed and collected for analysis using three-wave mixing rotational spectroscopy. The condensed vapor will consist only of the probe molecules that did not bind to the substrate, so there will be an excess of the enantiomer that did not bind as well with the substrate. There are several limitations inherent in the apparatus design. The simplicity of the setup allows for rapid assembly, and the equipment is inexpensive. However, depending on the identity of probe used, vapor pressures may be so low that suf cient distillate collection may be overly time-consuming. This potential issue could be remedied by the use of gentle heat or by increasing the ow rate of carrier gas, although these actions may make the predicted ee calculation less accurate. It is also possible for the vapor to exit the apparatus before it can suf ciently condense. This problem can be addressed by ensuring that the receiving ask is submerged in an ice bath or alternatively using rubber stoppers over the open arms of the round bottom ask.
eagent Selection The chiral probe chosen is , -propanediol because it forms two hydrogen bonds in many con gurations with -amino- -indanol AI , the substrate, due to its exible structure Figure . Other probe candidates considered were -phenylethanol, -butanol, and -butyn- -ol, but there were fewer possible intermolecular interactions for these molecules with AI, so the binding would be less pronounced. For example, -butyn-ol, is only capable of forming one type of interaction with AI based on the Three Point odel. The more interactions that are available, the more likely chiral discrimination will occur, meaning that the G will usually be larger and generate a larger ee. Additionally, there is evidence showing that , -propanediol produces suf cient separation using another separation method, chiral GC. To con rm the effectiveness of the three-wave mixing experiment, the low ee sample can also be analy ed with chiral GC. Previous research has shown that AI prefers one enantiomer over the other. Switching the enantiomer of the substrate should yield the opposite ee, so experiments with R, S - -cis-AI and S, R - - -AI should be performed to con rm that the substrate does have different binding with each enantiomer. Collection esults The apparatus was used to collect samples of , -propanediol from solutions of AI, and the results are summari ed in Table . ased on the thermodynamic calculations of chiral recognition, . would be observed for a ratio. However, AI did not readily dissolve in , -propanediol, and 3