The major product (A) formed in the following reaction is
` CH_(3) - overset( CH_3) overset(|) CH-CH_2 - underset(CH_(3))underset(|) overset(CH_(3)-CH_() -CH_(3) ) overset(|)N-overset( o+)CH_(2) -CH_(3) underset( Delta ) overset( OH^(-)) (A)`

Options

A. `CH_2 =CH_2`
B. `CH_3 underset(CH_3 ) underset(|) C = CH_(2)`
C. `CH_(3 ) -CH=CH_(2 )`
D. `CH_(3 ) - CH=CH_3`

Answer

To determine the major product (A) formed in the given reaction, we will follow these steps:

### Step 1: Identify the Reactant Structure
The given reactant is a quaternary ammonium compound with the following structure:
- A central nitrogen atom bonded to four carbon groups:
- One carbon is part of a CH3 group.
- Another carbon is part of a CH2 group.
- The other two carbons are part of CH3 groups.
- The nitrogen has a positive charge.

### Step 2: Understand the Reaction Conditions
The reaction is treated with a base (OH⁻) and heat (Δ). This indicates that we are likely dealing with a Hoffman elimination reaction, which typically involves the formation of an alkene from a quaternary ammonium salt.

### Step 3: Mechanism of Hoffman Elimination
In the Hoffman elimination:
1. The base (OH⁻) abstracts a proton (H⁺) from the carbon adjacent to the nitrogen (the alpha position).
2. The nitrogen will then lose its positive charge and form a double bond with the adjacent carbon, resulting in the formation of an alkene.

### Step 4: Identify Possible Products
Since we have a quaternary ammonium compound, we can consider the potential elimination of hydrogen atoms from the alpha positions:
1. The nitrogen can lose a hydrogen from the CH2 group.
2. The nitrogen can also lose a hydrogen from one of the CH3 groups.

### Step 5: Determine the Products
1. **Product 1**: If the hydrogen is removed from the CH2 group, we will form an alkene with the structure CH3-CH=CH2.
2. **Product 2**: If the hydrogen is removed from one of the CH3 groups, we will form an alkene with the structure CH2=CH-CH3.
3. **Product 3**: If the hydrogen is removed from the other CH3 group, we will form an alkene with the structure CH3-CH=CH2.

### Step 6: Analyze Substitution of Alkenes
According to Zaitsev's rule, the more substituted alkene is generally favored. However, in this case, we are looking for the major product, which will be the least substituted alkene:
1. **Alkene from CH2**: 1 substituent (CH3)
2. **Alkene from CH3**: 0 substituents (only H)
3. **Alkene from the other CH3**: 1 substituent (CH3)

### Step 7: Conclusion
The least substituted alkene, which will be the major product, is the one formed by removing the hydrogen from the CH2 group, resulting in the structure CH2=CH2 (ethylene).

Thus, the major product (A) formed in the reaction is:
**A = CH2=CH2**