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Part 3 Chemistry Extended Summary:

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. The nucleophile on an Sn2 reaction has to approach from behind due to the empty anti-bonding orbital on the central carbon. Otherwise, a bonding interaction cannot occur. 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. Christine and Lauren are approached from the back by Lisa, who is a nucleophile. After the three of them practice together in a representation of the transition state where the central carbon atom (Christine) is bonded to both the nucleophile (Lisa) and leaving group (Lauren) at the same time, Lisa kicks Lauren out of the group because she's a better fit for the group. All of this happens in one step, with Lisa approaching and Lauren leaving all at the same time.

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