SN2 and SN1

Also called

SN2 · SN1 · nucleophilic substitution · haloalkanes · bromoethane · tertiary bromide · backside attack · inversion of configuration · Walden inversion · carbocation · racemisation · racemic mixture · leaving group · nucleophile · hydroxide ion · primary and tertiary halides · transition state · हैलोऐल्केन · नाभिकस्नेही प्रतिस्थापन · कार्बधनायन

Topics

• Haloalkanes undergo nucleophilic substitution: a nucleophile replaces the halogen, which leaves as a halide ion.
• SN2 is one step: the nucleophile attacks the carbon from the side opposite the halogen as the C–X bond breaks.
• The other three groups swing through a flat transition state and end up inverted, like an umbrella in the wind.
• SN2 inverts the configuration (Walden inversion); primary halides and strong nucleophiles favour it.
• SN1 is two steps: the C–X bond breaks first, slowly, giving a planar carbocation; then the nucleophile adds.
• The nucleophile can add to either face of the flat carbocation, so a chiral halide gives a racemic mixture.
• Tertiary halides favour SN1: alkyl groups stabilise the carbocation and crowd the back of the carbon.
• Reactivity: SN1 3° > 2° > 1°, SN2 1° > 2° > 3°. Polar protic solvents such as water favour SN1.

About this model

A GLB file of about 246 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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