Precise-Source-Target Arrow (PSTA): A Modified Method for Drawing Curved Arrows in Organic Chemistry

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Kassem Hallal
Sami Tlais


Teaching; Organic Chemistry; Curved Arrows; Arrow Pushing; Mechanism


Curved arrows are indispensable explanatory tools routinely used by organic chemists to illustrate reaction mechanisms. However, for students, curved arrows are vague, useless, and difficult to understand owing to the ambiguity associated with their starting point or endpoint, leading to regioselectivity or formal charge uncertainty. The drawn curved arrows also affect students’ understanding of the electron flow processes in chemical reactions, forcing them to resort to memorization and rote learning. Given the importance of this study, it aimed to develop a modified method for drawing arrows to clarify the ambiguity associated with curved arrows and enhance students’ ability to understand and use them. This study also aimed to compare students' performance in predicting products of perplexing reaction patterns using traditional curved arrows and the new method to assess its efficiency. The newly developed method, Precise-Source-Target Arrows, (PSTA) was tested to locate the starting point (source) and endpoint (target) of drawn arrows and eliminate any regioselectivity or formal charge uncertainty. This study was conducted on 148 students enrolled in two organic chemistry courses at the Lebanese International University and used Edpuzzle videos to explain the new method and collect students’ responses to the embedded questions. The study found out that the PSTA method enhanced students' performance in predicting products and assigning charges compared to the traditional method and effectively clarified the uncertainties associated with a wide variety of arrow pushing patterns. It also enhanced students’ performance, their positive evaluation, high preference for using it as an alternative to the traditional method, and its applicability for a broad spectrum of mechanisms. The encouraging results of this preliminary study call for a more detailed study incorporating more reaction patterns, larger student samples, and an assessment of the short and long-term effects of using PSTA on student learning of reaction mechanisms.



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Abstract 103