The major product of the following reaction, if it occurs by SN2 mechanism is
Phenol + 1-bromo-3-met

Q: Why doesn't the double bond react?

The double bond is electron-rich, just like the phenoxide nucleophile. Nucleophiles attack electron-deficient centers, which in this case is the carbon attached to the electronegative bromine atom.

Q: Could an $S_N1$ reaction happen here?

Yes, allylic halides are excellent substrates for $S_N1$ reactions because the resulting allylic carbocation is resonance-stabilized. However, the question explicitly restricts us to the $S_N2$ pathway.

Q: What is the role of acetone?

Acetone is a polar aprotic solvent. It dissolves the reactants but does not strongly solvate the nucleophile (phenoxide ion) through hydrogen bonding. This keeps the nucleophile 'naked' and highly reactive, favoring the $S_N2$ mechanism.

Q: Why does the nucleophile attack the $CH_2$ group and not the tertiary carbon?

In an $S_N2$ mechanism, steric hindrance is the primary factor. The primary $CH_2$ carbon is much less sterically hindered than the tertiary carbon, making it the preferred site for backside attack.

Q: Why is $K_2CO_3$ used instead of a stronger base like NaOH?

$K_2CO_3$ is a mild base, perfectly suited to deprotonate phenol (which is a relatively strong weak acid, $pK_a \approx 10$) without causing unwanted side reactions that a stronger base might trigger.

Question

The major product of the following reaction, if it occurs by $S_N2$ mechanism is

Sigma Percentile · Accepted Answer

### Analyzing the Setup
We are given a reaction involving phenol and an allylic bromide, specifically 1-bromo-3-methylbut-2-ene. The reaction conditions specify the use of potassium carbonate ($K_2CO_3$) and acetone.

Our primary objective is to determine the major product, with a crucial constraint provided by the question: the reaction proceeds strictly via an $S_N2$ mechanism.

### The Role of the Base
The first step in this chemical journey is understanding the role of potassium carbonate. $K_2CO_3$ acts as a mild base.

Phenol is a weak acid, possessing an acidic proton on its hydroxyl group. The base abstracts this proton in an acid-base reaction.

This deprotonation generates the phenoxide ion ($PhO^-$). The oxygen atom now carries a full negative charge, transforming it into a highly potent nucleophile ready to seek out an electron-deficient center.

### The Master Equation: $S_N2$ Execution
With our nucleophile ready, we turn our attention to the alkyl halide. Acetone, a polar aprotic solvent, is the perfect environment for this. It dissolves the reactants but does not strongly solvate the phenoxide ion, keeping its nucleophilicity high.

The question explicitly dictates an $S_N2$ mechanism. In an $S_N2$ reaction, the nucleophile attacks the electrophilic carbon from the backside, and the leaving group departs simultaneously in a single, concerted step.

**Crucially, no carbocation intermediate is formed.** The phenoxide oxygen directly attacks the primary carbon attached to the bromine atom, pushing the bromide ion out.

### Final Calculation and Conclusion
As the bromide leaves, the oxygen forms a new, stable ether bond with the $CH_2$ group.

Because the reaction is strictly $S_N2$, the rest of the allylic chain remains completely unchanged. There is no opportunity for the double bond to shift or for carbocation rearrangements to occur.

The final resulting product is **phenyl 3-methylbut-2-enyl ether**. Comparing this structure to our given options, it perfectly matches option (d).

### The Way Forward
It is worth pondering: what if the $S_N2$ mechanism wasn't specified? Allylic halides are notorious for undergoing $S_N1$ reactions because they can form highly stable, resonance-delocalized allylic carbocations.

If an $S_N1$ pathway were allowed, we would likely see a mixture of products, including attack at the more substituted tertiary carbon. However, the strict $S_N2$ constraint simplifies our path, leading directly to the un-rearranged substitution product. Always read the reaction conditions carefully!

Animated Solution for Chemistry - Organic Chemistry: The major product of the following reaction, if it occurs by $S_{N} 2$ mechanism is

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Visualized Solution

Analyzing the Reactants

Role of $K_{2} CO_{3}$

Formation of Phenoxide Ion

$S_{N} 2$ Attack