A Level Chemistry OCR Practice Exam

What is the termination step in a radical substitution reaction?

1. The step where a radical starts a reaction

2. The step where two radicals combine to form a molecule

3. The step where reactants are converted to products

4. The step where intermediates are formed

The correct answer is: The step where two radicals combine to form a molecule

In a radical substitution reaction, the termination step is characterized by the combination of two radicals to form a stable molecule. This process effectively terminates the reaction because it reduces the number of reactive radicals in the system. When two radicals collide, they can share their unpaired electrons to form a new covalent bond, resulting in a non-radical product. This step is crucial as it brings the radical chain mechanism to an end, ultimately leading to the formation of stable products. Radical mechanisms involve initiation, propagation, and termination steps. The initiation step generates radicals, the propagation steps allow for the continuation of radical reactions, while the termination step specifically addresses the reduction of radical species. Understanding this final step is essential when analyzing the complete mechanism of radical substitution reactions.