Using Trityl Carbocations to Introduce Mechanistic Thinking to German High School Students

Catharina Schmitt,Michael Schween

doi:10.12691/wjce-6-1-4

Abstract

Mechanistic problem-solving is the scientific core competence of organic chemistry. Hence, many students struggle with developing multivariate mechanistic thinking. They very often rely on memorized rules and propose products without providing a detailed mechanistic pathway. They simply apply problem-solving strategies from general chemistry, which is more product-oriented than organic chemistry. A process-oriented view that is highly demanded in organic chemistry requires the understanding and connection of basic principles and concepts. In order to practice the process-oriented approach and introduce advanced German high school students to mechanistic thinking, we developed a set of three new experiments to generate carbocations in model reactions for the observation of reactive intermediates. Trityl cations proved to be the best ones for an experimental investigation of a reaction’s progress which is accessible with a simple analysis that generates explicit results by changes in color and electric conductivity. The experiments are arranged in a guided inquiry workshop of six steps alternating theoretical (oral group discussions) and experimental phases.

Highlights

Mechanistic problem-solving is one of the most challenging tasks for students in organic chemistry
We developed three key experiments as contrasting cases focusing on carbocations in order to practice the process-oriented view of organic chemistry and to put the focus on the mechanistic pathway and its underlying concepts
A single experiment or workshop can only tackle this problem, but as the results show, it is very beneficial for high school students to start with practicing mechanistic thinking already at high school

Summary

Introduction

Mechanistic problem-solving is one of the most challenging tasks for students in organic chemistry. Proposing mechanisms is one form of mechanistic problem-solving and it requires deep understanding and connecting of different chemical basic concepts. Many students fail to predict the mechanism of reactions and give the products [2]. This corresponds closely to the thinking in general chemistry, which is mostly product-oriented. Organic chemistry takes a more processoriented view, focusing on the mechanistic pathway between reactants and products [3]. Moving on from general chemistry to organic chemistry, the molecular transformations that are taking place during a reaction move into focus.

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Conclusion