Which reaction produce 1-methylcyclohexene

Options

A.
`overset((i) aq.KOH)underset((ii) CH_3MgBr,"ether",(iii)H^(+),H_2O)to`
B.
`overset((i)HBr) underset((ii)"alcoholic " KOH.Delta)to`
C.
`overset((i)Mg,"ether")underset((ii)CH_2O,(iii)H^(+),H_2O)to`
D.
`overset((i)HI)underset((ii)aq. NaOH)to`

Answer

To determine which reaction produces 1-methylcyclohexene, we need to analyze the provided options step by step.

### Step-by-Step Solution:

1. **Understanding the Product**:
- The target product is 1-methylcyclohexene. This means we have a cyclohexene ring with a methyl group attached to the first carbon of the double bond.

2. **Analyzing the First Option**:
- The first option involves a dibromocyclohexane reacting with aqueous KOH followed by a Grignard reagent (CH3MgBr).
- The aqueous KOH will replace the bromine atoms with hydroxyl groups, leading to a diol.
- The diol will then undergo dehydration to form a ketone-like structure, which is not the desired product. Thus, the first option does not yield 1-methylcyclohexene.

3. **Analyzing the Second Option**:
- The second option starts with a cyclohexyl bromide reacting with HBr.
- This reaction will form a carbocation. The more stable carbocation will be formed at the tertiary position due to the presence of a methyl group.
- The bromide ion will then attack the carbocation, leading to the formation of a bromo compound.
- When treated with alcoholic KOH, the base will abstract a hydrogen atom, resulting in the formation of 1-methylcyclohexene. This option successfully yields the desired product.

4. **Analyzing the Third Option**:
- The third option involves a Grignard reagent reacting with a compound to form an alcohol.
- The product from this reaction will not lead to the formation of 1-methylcyclohexene but rather an alcohol, which is not the target product.

5. **Analyzing the Fourth Option**:
- The fourth option also involves a carbocation formation but leads to a different product when treated with aqueous NaOH.
- The product formed here is an alcohol, not 1-methylcyclohexene.

### Conclusion:
After analyzing all options, we find that the **second option** is the correct reaction that produces **1-methylcyclohexene**.