Reaction Pathway (Mermaid Diagram)

Selectivity of H-Abstraction

Stability of radical intermediate:

$\text{3° radical} > \text{2° radical} > \text{1° radical} > \text{methyl radical}$

This is because higher substitution provides more hyperconjugation stabilization of the $sp^{2}$-hybridized radical center.

Halogen selectivity (3° vs 1° H per-H ratio):

• $Br_{2}$: ~1600:1 (very high selectivity)
• $Cl_{2}$: ~5:1 (moderate selectivity)
• $F_{2}$: ~1:1 (no practical selectivity — too reactive)

Key Propagation Reactions (General)

$\text{R–H} + \text{X}^{\bullet} \xrightarrow{\Delta} \text{R}^{\bullet} + \text{HX} \quad \text{(H abstraction)}$

$\text{R}^{\bullet} + \text{X}_2 \rightarrow \text{R–X} + \text{X}^{\bullet} \quad \text{(product formation)}$