Substitution and Elimination Reactions in Living Organisms
Start with the big picture
Biological organohalide chemistry is shaped by enzymes that favor nucleophilic substitution or elimination and reductive dehalogenation; free-solution S_N1/E1 pathways are uncommon in the cellular environment. Haloalkane dehalogenases, glutathione S-transferases, and L-2-haloacid dehalogenases illustrate distinct forms of substitution. Reductive dehalogenases cleave carbon–halogen bonds through electron transfer, while halogenating enzymes install halogens during biosynthesis or through peroxidase systems. Thyroid deiodinases provide a specialized example of reductive dehalogenation with a role in hormone regulation. The lesson also considers how substrate positioning, transition-state stabilization, and leaving-group ability influence biological reactivity.
What you'll learn
- Distinguish common enzyme-mediated organohalide reactions from rare S_N1/E1 pathways.
- Describe the catalytic sequence of haloalkane dehalogenases.
- Compare organohalide substitution by GSTs and L-2-haloacid dehalogenases.
- Explain the roles of reductive dehalogenation and enzymatic halogenation.
- Relate thyroid deiodinase activity and leaving-group ability to biological function.
Continue your study
Work through the complete notes and reinforce the topic with the study tools available in the full lesson.
