Why are methyl radicals short-lived?

Methyl radicals are short-lived because they are highly reactive species containing a single, unpaired electron. Because of this odd electron, they possess a strong tendency to achieve stability by pairing their electrons.1

They typically disappear rapidly and spontaneously through several processes:

• Dimerization: Methyl radicals frequently combine with one another to form ethane ($C{H}_{3}C{H}_3$).23
• Chemical Reaction: They react readily with other atoms or molecules, such as abstracting hydrogen from organic solvents to form methane or reacting with metals and other radicals to form stable compounds.123

Due to this high reactivity, methyl radicals exist only as transient intermediates in chemical processes, such as chain reactions or high-temperature reactions, rather than as stable, long-term substances.2