A Student-Friendly Approach to Introduce the Evolution of Planar Chirality

Chirality continues to intrigue scientists because of its implications in various scientific areas, including the long-unsolved question of its development and link with the origin of life. Chirality plays a significant role in medicine with the advent of chiral drugs and the consequent importance of asymmetric synthesis. For many undergraduate students, stereochemistry, in particular chirality, is challenging, because the topic is highly conceptual, requiring virtual visualization of a molecule in 3-dimensions, contrasting with normal 2-dimensional representations on paper, a board, or a computer screen. Among the various types of chirality, planar chirality is perhaps the most difficult to grasp. Understanding this topic as well as the associated term "chirality plane" (sometimes referred to as a "chiral plane" in textbooks) can be problematic. In this manuscript, we introduce an alternative approach to explain the geometrical requirements leading to the occurrence of planar chirality based on the "dimensional chiral simplex" concept. This pedagogical approach may be better than the standard textbook-based method, as established through a logical comparison of the student performance in a multiple-choice question based test on planar chirality, conducted before and after the dimension-based idea was taught. Moreover, the difference between axial chirality in biaryl systems and planar chirality in cyclophanes, ansa compounds, etc., is explained. The teaching of "atropisomerism", which is generally reserved for biaryls with restricted rotation, is described in relation to compounds with planar chirality.