What Happens When Two Radicals Meet? A Practical Approach to Free Radical Reaction Mechanisms

Abstract

Molecular modeling can be used as an excellent teaching method for providing better insight into the mechanism of free radical reactions. Due to its highly visual nature, it can affect and improve students' perception and visualization of chemistry phenomena. The majority of chemistry students will know how to represent a reaction between two free radicals symbolically (either with electron pushing arrows or with the representation of the paired and unpaired electrons). However, the problem arises when they are asked to explain what happens between the radicals at the microscopic level. In some elementary chemical reactions the reactants and products differ in spin multiplicity. Thus, these reactions need to be described in terms of two-state reactivity. Such a reaction occurs on two spin surfaces and includes spin inversion along the reaction coordinate. In this work, we demonstrate a procedure that aims to explain the progression of a coupling reaction between two radicals yielding toluene. This example showcases how one singlet molecule can be obtained from two doublets. To verify the impact of molecular modeling on students' knowledge about free radical reactions, we conducted a study that involved 44 chemistry students. The three questionnaires, two knowledge tests (pretest and post-test), and one survey were carried out to obtain the data. The obtained data imply that this practical approach has a significant impact on students' knowledge and can help them to better understand the free radical reactions, particularly at the microscopic level.