The major product of the following reaction is :
H3C-C(CH3)=CH-CH2-CH2-C(CH3)(OH)-CH=CH2 + Dil. H2SO

Q: Why does the positive charge shift to the primary carbon? Isn't tertiary more stable?

While a tertiary carbocation is generally more stable, the primary allylic carbocation is in equilibrium with it due to resonance. The cyclization from the primary position forms a stable six-membered ring, which drives the reaction forward.

Q: Why doesn't the double bond attack the tertiary carbocation directly?

If the double bond attacked the tertiary carbocation directly, it would form a highly strained four-membered or five-membered ring. Six-membered rings are much more stable and kinetically favored.

Q: What is the role of dilute sulfuric acid?

The acid provides the proton needed to turn the $-OH$ group into a good leaving group ($-OH_2^+$). Being dilute means there is enough water present to act as a nucleophile in the final step.

Q: Could the reaction proceed via an $S_N2$ mechanism?

No, the substrate is a tertiary alcohol, which is too sterically hindered for an $S_N2$ attack. Furthermore, the acidic conditions strongly favor the formation of a carbocation ($S_N1$/$E1$ pathway).

Q: What would happen if we used concentrated acid and heat?

Concentrated acid and heat would favor elimination over substitution. The final tertiary alcohol would likely dehydrate again, forming a diene product like limonene.

Question

The major product of the following reaction is :

Sigma Percentile · Accepted Answer

### Analyzing the Setup

Imagine you are looking at a complex organic molecule, a diene with a tertiary alcohol group, specifically **linalool**. We are treating this molecule with dilute sulfuric acid ($H_2SO_4$).

Whenever you see an alcohol in an acidic medium, your first instinct should be protonation. The acid acts as a catalyst, turning the poor hydroxyl leaving group into an excellent leaving group: water.

### The Reaction Mechanism

Let's break down the mechanism step-by-step. First, the oxygen atom of the hydroxyl group grabs a proton ($H^+$) from the acid. This forms an $-OH_2^+$ group, which promptly leaves as a neutral water molecule. The departure of water leaves behind a **tertiary carbocation**.

Now, look closely at this carbocation. It is not just any carbocation; it is an **allylic carbocation**. This means it is situated right next to a carbon-carbon double bond, allowing it to be stabilized by resonance. Through resonance, the $\pi$ electrons shift, and the positive charge moves to the terminal carbon atom.

$$ 	ext{Tertiary Allylic Carbocation} \leftrightarrow 	ext{Primary Allylic Carbocation} $$

You might wonder, why would the positive charge move to a less stable primary position? The answer lies in the geometry of the molecule. The primary carbocation is perfectly positioned for an **intramolecular attack**. The isolated double bond on the other side of the molecule swoops in and attacks this terminal positive charge. This cyclization forms a highly stable **six-membered cyclohexene ring**.

### The Final Product

After the ring closes, a new tertiary carbocation is generated on the side chain. Since we are in a dilute acidic medium, there is plenty of water around. A water molecule attacks this new carbocation. After a quick deprotonation step, we are left with a new tertiary alcohol group.

The final product of this elegant cyclization is **$\alpha$-terpineol**. When we compare our derived structure with the given options, it perfectly matches option (c).

This reaction is a beautiful example of how resonance and intramolecular forces can drive a molecule to rearrange itself into a completely new cyclic structure!

Animated Solution for Chemistry - Organic Chemistry: The major product of the following reaction is :

Select Answer:

Visualized Solution

$V i s u a l A n c h or$

$L o g i c B r i d g e$

$R a w S e t u p$

$A t o mi c C o m p u t e : R eso nan ce$

$A t o mi c C o m p u t e : C y c l i z a t i o n$

$A t o mi c C o m p u t e : H y d r a t i o n$

$F ina l A n s w er$

$T h e W a y F or w a r d$

The Sigma Insight: Alcohols, Phenols, Ethers

Analyzing the Setup

The Reaction Mechanism

The Final Product

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