Consider the reaction
`[CH_(3)CH_(2)CH_(2)-underset(CH_(3))underset(|)overset(CH_(3))overset(|)(.^(o+)(N))-CH_(2)CH_(3)]OH^(-)overset("Heat")(to)`
Which of the following is formed in major amount ?

Options

A. `CH_(2)=CH_(2)`
B. `CH_(3)CH=CH_(2)`
C. Both (A) and (B) in equal amount
D. None, as no reaction takes place

Answer

To solve the given problem, we need to analyze the reaction involving a quaternary amine undergoing Hoffman elimination. Here’s a step-by-step breakdown of the solution:

### Step 1: Identify the Reactant
The reactant is a quaternary amine, which has the structure:
\[ [CH_3CH_2CH_2-CH(CH_3)(N)-CH_2CH_3] \]
This compound contains a nitrogen atom bonded to four carbon groups.

### Step 2: Understand the Reaction
The reaction is a Hoffman elimination, where heating a quaternary amine leads to the formation of a tertiary amine and an alkene. The general reaction can be represented as:
\[ \text{Quaternary Amine} \xrightarrow{\text{Heat}} \text{Tertiary Amine} + \text{Alkene} \]

### Step 3: Determine the Products
In this case, we need to identify the possible alkenes that can be formed. The quaternary amine can lose a hydrogen atom from one of the carbon atoms adjacent to the nitrogen, resulting in the formation of two possible alkenes:
1. Ethene (from the ethyl group)
2. Propene (from the propyl group)

### Step 4: Analyze Substitution of Alkenes
In the context of alkenes, we need to consider the degree of substitution:
- Ethene is a less substituted alkene (only 2 carbons).
- Propene is a more substituted alkene (3 carbons).

According to Zaitsev's rule, the less substituted alkene is favored in Hoffman elimination reactions.

### Step 5: Identify the Major Product
Since ethene is the less substituted alkene, it will be formed in a major amount compared to propene. Therefore, the major product of the reaction is:
- Ethene (C2H4)

### Step 6: Identify the Tertiary Amine
The tertiary amine formed from the reaction will have the structure:
\[ (CH_3)_2CH-CH_2 \]
This corresponds to a tertiary amine with two methyl groups and one propyl group.

### Conclusion
The major product formed in the reaction is:
- **Ethene** (C2H4)

### Final Answer
The correct option is **A: Ethene**.

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