Advanced Topic 788 of 1102 Organic Chemistry
SN2 Reaction
A one-step bimolecular substitution with backside attack and inversion of configuration.
In-depth explanation of SN2 Reaction
The SN2 reaction is a one-step bimolecular nucleophilic substitution in which a nucleophile attacks the carbon from the side opposite the leaving group. The rate law is rate equal to k times the haloalkane concentration times the nucleophile concentration, reflecting the single concerted transition state. The nucleophile approaches from the back, so the stereochemistry is inverted in a process called Walden inversion. It is favoured by methyl and primary substrates, strong nucleophiles and polar aprotic solvents such as acetone or DMSO, while hindered substrates react slowly.
Going deeper: SN2 Reaction
Key ideas: Bimolecular, single-step backside attack with inversion of configuration (Walden inversion); rate equals k times halide times nucleophile. Reactivity: methyl > primary > secondary >> tertiary because of steric hindrance. Favoured by strong nucleophiles and polar aprotic solvents (DMSO, DMF, acetone) that leave the nucleophile unsolvated. Needs a good leaving group (I > Br > Cl >> F).
Common mistakes and connections: Students think the transition state is an intermediate; it is a pentacoordinate state with partial bonds. Another mistake is expecting SN2 at a tertiary or sp2 carbon. Neopentyl halides, though primary, react very slowly. Links to Williamson ether synthesis, the Finkelstein reaction and nucleophile strength.
Visualization of SN2 Reaction
The nucleophile attacks from the back as the leaving group leaves in a single concerted step, inverting the stereocentre. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Bromoethane reacts with cyanide ion by SN2 to give propanenitrile, CH3CH2Br plus CN- giving CH3CH2CN.
Frequently asked questions about SN2 Reaction
What is SN2 Reaction?
A one-step bimolecular substitution with backside attack and inversion of configuration.
Is SN2 Reaction a beginner, intermediate or advanced topic?
SN2 Reaction is a advanced topic in Organic Chemistry. It builds on beginner and intermediate topics, so review those first if needed.
What should I learn before SN2 Reaction?
Study these earlier topics in Organic Chemistry first: Directing Effects, Haloalkanes, SN1 Reaction.
What comes after SN2 Reaction?
The next topics in Organic Chemistry are E1 Elimination and E2 Elimination.
Can I practise SN2 Reaction with quizzes?
Yes. The interactive lesson includes a self-check question on SN2 Reaction, and the Organic Chemistry quiz draws on every topic in this area.
Where SN2 Reaction fits in Organic Chemistry
SN2 Reaction is topic 60 of 148 in Organic Chemistry.