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Help me! I'm Diene!

Teaching Organic Chemistry through Fiction


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Sn Reactions - Concept Explanation - Pt 3: Sn2 Reactions: What are they?
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Part Three Concept Explanation:
Sn2 Reactions; What are they?


An important type of reaction in organic chemistry is a nucleophilic substitution reaction, where a nucleophile replaces another nucleophile on a central carbon atom. Bimolecular nucleophilic substitution reactions, or Sn2 reactions, occur in one step; the rate determining step of an Sn2 reaction consists of two nucleophiles. Therefore, an Sn2 reaction has a state where there are two nucleophilies attached to the central carbon atom at once.

An Sn2 reaction occurs when a nucleophile attacks from the backside of the molecule, kicking out the leaving group in front. Thus, there is a point during the Sn2 reaction where there exists a transition state, a point where both are attached yet not attached to the central carbon atom. This is a state unique to Sn2 chemistry.

Sn2 reactions typically do not occur on tertiary carbons, as the substituents attached to the central carbon atom hinder the nucleophile from attacking the back due to the fact that they are there taking up space. Therefore, Sn2 reactions typically happen on primary carbons and occasionally on secondary carbons.

Lisa serves as the nucleophile in the case of this reaction. Her arrival takes Christine and Lauren by surprise as she approaches from the back. After they practice together, all three of them, in a representation of the transition state where the central carbon atom (Christine) is bonded to both the nucleophile and leaving group (Lisa and Lauren respectively), Christine agrees to kick Lauren out of the group because she finds Lisa a better fit for the band (or molecule).

Back to Part Three
Continue to Part Four
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