The missing structures A and B in the reaction sequence :
`CH_(3) - CH = CH_(2) overset(B_(2)H_(6))to A overset (H_(2)O_(2)+NaOH) to B ` are given by the set :

Options

A. `CH_(3) - CH_(2) - CH_(2) - BH_(2), CH_(3) - CH_(2) - CH_(2) OH`
B. `(CH_(3) - CH_(2)-CH_(2))_(3) B, CH_(3) - CH_(2) - CH_(2)OH`
C. `(CH_(3))_(2) CH - CH_(2) - _(2), CH_(3) - CH(OH) - CH`
D. `(CH_(3) CHCH)_(2) BH, CH_(3)-CH_(2) - CH_(2) OH`

Answer

To determine the missing structures A and B in the reaction sequence involving the alkene CH₃-CH=CH₂, we will analyze the hydroboration-oxidation reaction step by step.

### Step 1: Identify the starting material
The starting material is the alkene CH₃-CH=CH₂. This is propene, which has a double bond between the second and third carbon atoms.

### Step 2: Hydroboration with B₂H₆
When propene reacts with diborane (B₂H₆), hydroboration occurs. In this reaction, the boron atom adds to the less substituted carbon atom of the double bond.

- **Mechanism**: The boron atom from B₂H₆ will preferentially add to the terminal carbon (the less substituted carbon), resulting in the formation of an alkyl borane.

The structure of A after hydroboration will be:
\[ \text{A: CH}_3-\text{CH}_2-\text{CH}_2\text{B}(\text{H})_2 \]
This structure indicates that the boron atom is attached to the primary carbon, resulting in the formation of tri-n-butylborane.

### Step 3: Oxidation with H₂O₂ and NaOH
The next step involves the oxidation of the alkyl borane (structure A) using hydrogen peroxide (H₂O₂) and sodium hydroxide (NaOH).

- **Mechanism**: In this step, the boron atom is replaced by a hydroxyl group (-OH) through an oxidation process. The reaction leads to the formation of an alcohol.

The structure of B after oxidation will be:
\[ \text{B: CH}_3-\text{CH}_2-\text{CH}_2\text{OH} \]
This indicates that we have formed butanol as the final product.

### Summary of Structures
- **Structure A**: CH₃-CH₂-CH₂B(H)₂ (alkyl borane)
- **Structure B**: CH₃-CH₂-CH₂OH (butanol)

### Final Answer
The missing structures A and B in the reaction sequence are:
- **A**: CH₃-CH₂-CH₂B(H)₂
- **B**: CH₃-CH₂-CH₂OH