Consider the following statements about S_N 2 reactions:
1. They are bimolecular reactions.
2. They proceed with inversion of configuration. complete
3. They involve the formation of an intermediate.
4. No rearrangement is involved in them.
Select the correct answer from the codes given below.

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UP LT Grade Teacher (Science) 2018 Official Paper

Answer 1

CONCEPT:

SN₂ Reaction

SN₂ reactions are bimolecular nucleophilic substitution reactions.
They follow a one-step mechanism where the nucleophile attacks the substrate and the leaving group departs simultaneously.
The reaction leads to inversion of configuration, known as the "Walden inversion."
No rearrangements occur in SN₂ reactions because there is no carbocation intermediate involved.

EXPLANATION:

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Statement 1: "They are bimolecular reactions."
- Correct. SN₂ reactions involve two species (nucleophile and substrate) participating in the rate-determining step.
Statement 2: "They proceed with inversion of configuration."
- Correct. The backside attack by the nucleophile causes inversion of the stereochemistry of the product.
Statement 3: "They involve the formation of an intermediate."
- Incorrect. SN₂ reactions do not involve the formation of a carbocation or any other intermediate; the reaction proceeds in a single concerted step.
Statement 4: "No rearrangement is involved in them."
- Correct. Since SN₂ reactions lack a carbocation intermediate, rearrangements do not occur.

The correct option is 4, "Only 1, 2 and 4 are correct."