why is an ethyl radical more stable than a methyl radical?
The unpaired electron in the ethyl radical can be more easily delocalized by two carbon atoms, and through the increase in the number of resonance forms in a two-carbon chain.
The stability of a radical is influenced by several factors, including electron delocalization, hyperconjugation, and resonance. In the case of an ethyl radical (·CH2-CH3) compared to a methyl radical (·CH3), the ethyl radical is generally considered to be more stable. Here's why:
1. Electron delocalization: In a radical, an unpaired electron is present on a carbon atom. In the ethyl radical, this unpaired electron is shared between two carbon atoms (·CH2-CH3), whereas in the methyl radical, it is localized on a single carbon atom (·CH3). The sharing of the unpaired electron in the ethyl radical allows for greater electron delocalization and can stabilize the radical.
2. Hyperconjugation: Hyperconjugation occurs when the overlap of the σ-bonding orbital of a neighboring carbon-hydrogen (C-H) bond interacts with the vacant p-orbital of the radical carbon atom. In the ethyl radical, there are two additional C-H bonds compared to the methyl radical, meaning there are more C-H orbitals available for hyperconjugation. These additional interactions can increase electron density around the radical carbon, thereby enhancing stability.
3. Resonance: Resonance refers to the delocalization of electrons through pi (π) bonds. In the case of the ethyl radical, the unpaired electron can be delocalized across the entire ethyl group due to resonance, whereas in the methyl radical, resonance is not possible. This resonance effect contributes to the stability of the ethyl radical.
To summarize, the ethyl radical is more stable than the methyl radical due to the presence of electron delocalization, increased hyperconjugation, and resonance effects resulting from the additional carbon atom in the ethyl group.