Chapter 9: Free Radical Substitution Reaction of Alkanes

Generally speaking, alkane is the type of compound that is inert in most organic reactions. There are only C-C and C-H σ bonds involved in the structure of alkanes. A σ bond is formed by head-to-head orbital overlapping, which is the most effective way of overlapping, as it makes the bond strong and stable. Furthermore, both C-C and C-H bonds are non-polar, so none of the atoms has any significant charges, which means no nucleophile nor electrophile is possible in alkanes. Overall, alkanes are rather unreactive compounds, and they rarely undergo any organic reactions. One exception is the reaction we will learn about in this chapter, which is halogenation substitution via a radical mechanism. We will first talk about how to produce radicals and then see radicals promote the substitution reaction of alkanes.

Learning Objectives for this chapter:

• Understand, explain and show the radical substitution mechanism of alkanes, including the intermediates, transition state and reaction coordination diagram.
• Explain the process of radical formation, and compare the properties, stability and reactivity of different types of alkyl radicals.
• Understand the reactivity difference between different halogens, and how the difference affects the application of radical substitution reaction.