`1`-Bromobutane is treated with sodium ethoxide in ethanol. The major product obrained is

Options

A. trans-but-`2`-ene
B. cis-But-`2`-ene
C. but-`1`-ene
D. `1`-ethoxybutane

Explanation

To determine the major product obtained when 1-bromobutane is treated with sodium ethoxide in ethanol, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Reactants**: The reactant is 1-bromobutane, which has the structure:
\[ \text{CH}_3\text{CH}_2\text{CH}_2\text{CH}_2\text{Br} \]
Here, the bromine (Br) is attached to the first carbon of the butane chain.

2. **Understand the Reaction Conditions**: Sodium ethoxide (NaOEt) is a strong base and ethanol (EtOH) is the solvent. Under these conditions, the reaction will likely proceed via an elimination mechanism (E2).

3. **Determine the Mechanism**: Since we are dealing with a strong base (sodium ethoxide), the elimination reaction will occur via the E2 mechanism. In E2, the base abstracts a proton (H) from a β-carbon (the carbon adjacent to the carbon with the leaving group), and the leaving group (Br) departs simultaneously.

4. **Identify β-Hydrogens**: In 1-bromobutane, the β-carbons are the second and third carbons in the chain. The β-hydrogens available for abstraction are:
- From the second carbon: 2 hydrogens
- From the third carbon: 2 hydrogens

5. **Elimination to Form Alkene**: The elimination can occur by removing a hydrogen from either the second or third carbon.
- If we remove a hydrogen from the second carbon, we would form but-2-ene:
\[ \text{CH}_3\text{CH}=\text{CH}\text{CH}_3 \]
- If we remove a hydrogen from the third carbon, we would also form but-2-ene.

6. **Determine the Major Product**: Since both pathways lead to the formation of but-2-ene, we need to consider the stability of the alkene. But-2-ene can exist as two isomers: cis and trans. The trans isomer is generally more stable due to less steric hindrance. Therefore, the major product is trans-but-2-ene.

7. **Final Answer**: The major product obtained from the reaction of 1-bromobutane with sodium ethoxide in ethanol is **trans-but-2-ene**.