ROH does not react with NaBr, but adding H2 SO4 forms RBr. Explain. Br^-, an extremely weak Brön

step 1 Addition of hydrogen on double pond of propene yields isopropyl iodide and not N propyl iodide a

ROH does not react with NaBr, but adding H2 SO4 forms RBr....

ROH does not react with $\mathrm{NaBr}$, but adding $\mathrm{H}_2 \mathrm{SO}_4$ forms $\mathrm{RBr}$. Explain. $\mathrm{Br}^{-}$, an extremely weak Brönsted base. cannot displace the strong base $\mathrm{OH}^{-}$. In acid, $\mathrm{ROH}_2$ is first formed. Now, $\mathrm{Br}^{-}$displaces $\mathrm{H}_2 \mathrm{O}$, which is a very weak base and a good leaving group.

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Key Concepts

Acid Catalysis

Acid catalysis involves using an acid to protonate a functional group, thereby enhancing its reactivity. In the context of converting an alcohol to an alkyl bromide, the acid protonates the hydroxyl group (–OH), transforming it into water (H?O), a much better leaving group.

Leaving Group Ability

The effectiveness of a leaving group is critical in substitution reactions. By protonating the alcohol, the hydroxyl group becomes a water molecule, which is a weak base and an excellent leaving group. This enhancement facilitates the substitution reaction where water is displaced by the nucleophile.

Bronsted Acid-Base Concept

The Bronsted acid-base theory focuses on proton transfer between species. In this reaction, the strong acid donates a proton to the alcohol (a weak base), forming a protonated intermediate. This step prevents the more basic hydroxyl ion from interfering and allows the weak base bromide ion to perform the nucleophilic attack.

Nucleophilic Substitution Mechanism

The nucleophilic substitution mechanism under acid catalysis involves the initial protonation of the alcohol to create a better leaving group, followed by the attack of a nucleophile, in this case, the bromide ion. This process leads to the replacement of the leaving group by the nucleophile, resulting in the formation of the desired alkyl bromide.

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