Visualizing Molecular Chirality in the Organic Chemistry Laboratory Using Cholesteric Liquid Crystals

Abstract

Although stereochemistry is an important topic in second-year undergraduate organic chemistry, there are limited options for laboratory activities that allow direct visualization of macroscopic chiral phenomena. A novel, guided-inquiry experiment was developed that allows students to explore chirality in the context of cholesteric liquid crystals. As part of the experiment, which requires no specialized equipment, students visually distinguish two enantiomers. A chiral imine is synthesized in one step from an assigned (but unknown to students) enantiomer of 1-phenylethylamine and then dissolved in a nematic liquid crystal host, inducing a helical structure. The resulting cholesteric liquid crystalline material selectively reflects circularly polarized light with a handedness that depends on the absolute configuration of the starting amine, easily detected using circularly polarizing filters from disposable 3D glasses. Working in teams, students examine the behavior of both dopant enantiomers and the racemic mixture. Analysis of our students’ responses to post-lab questions indicates comprehension of most of the ideas introduced in lab.

Thermotropic Liquid Crystal-Assisted Chemical and Biological Sensors

“…Nematic LCs, such as 5CB, can be turned into chiral (N* or cholesteric LCs) when mixed with chiral dopants [ 4 , 48 , 87 ]. The response of cholesteric films in contact with aqueous solutions of surfactants is rather peculiar (See Figure 13 ).…”

“…Cholesteric LCs may provide relatively inexpensive, efficient and highly sensitive gas or environmental sensors [ 4 , 12 , 87 , 88 ] based on the ability of cholesteric phases to selectively reflect polarized light. An important application could be to detect the presence of specific volatile organic compounds (VOC) in the human body that can serve as a biomarker for certain diseases, such as lung cancer and diabetes [ 89 , 90 , 91 , 92 ].…”

An in-depth Study of the Concept of Chirality in Organic and Pharmaceutical Chemistry: Using Crystal Structure Data with 3D Visualization Software

“…In the future teaching process, we will search and use more novel auxiliary means. Other researchers have provided us with many options, such as the cholesterol liquid crystals method, the crystalline sponge method and the paper helicopter method, [41][42][43] as well as other more intuitive methods to enable students to learn to understand the concept of chirality. We believe that diversified teaching methods can improve students' interest and memory of knowledge.…”

Real-Time Interactive Simulation and Visualization of Organic Molecules

“…A mental picture of atomic-scale phenomena is essential to develop this skill, but there is no microscope that can provide a movie of atomic-scale phenomena in general. This makes it difficult to design lab activities to teach molecular concepts and help students connect them to macroscopic phenomena. , Computer generated visualizations can serve this purpose and are regularly employed in chemistry courses to build students’ intuition about atomic effects. Physically accurate molecular behavior can be generated with first-principles simulations, and visualizations of such simulations have been in regular use since the mid-1990s. − These visualizations can be instrumental in making abstract concepts accessible and building understanding of microscopic chemical phenomena in both students and researchers alike. − …”

“…This makes it difficult to design lab activities to teach molecular concepts and help students connect them to macroscopic phenomena. 6,7 Computer generated visualizations can serve this purpose and are regularly employed in chemistry courses to build students' intuition about atomic effects. Physically accurate molecular behavior can be generated with first-principles simulations, and visualizations of such simulations have been in regular use since the mid-1990s.…”