Consider the following sequence of reaction and identify the final product (Z).
`CH_3-CH=CH_2overset(HBr)(rarr)(P)overset(aq.NaOH)(rarr)(Q)underset(K_2Cr_2O_7//H^+)overset("oxidation")(rarr)(R )`

Options

A. `CH_3CH_2CH_3`
B. `CH_3CH_2CHO`
C. `CH_3CH_2COOH`
D. `CH_3COCH_3`

Answer

To solve the problem, we need to analyze the sequence of reactions step by step.

### Step 1: Addition of HBr to Propene
The starting compound is propene (CH₃-CH=CH₂). When HBr is added to propene, it undergoes an electrophilic addition reaction. The double bond between the carbon atoms breaks, and a bromine atom and a hydrogen atom are added across the double bond.

- The addition of HBr follows Markovnikov's rule, which states that the hydrogen atom will attach to the carbon with the greater number of hydrogen atoms (the less substituted carbon), leading to the formation of a more stable carbocation.
- In this case, the more stable secondary carbocation is formed at the second carbon atom.

**Intermediate Product (P):** CH₃-CHBr-CH₃ (2-bromopropane)

### Step 2: Reaction with Aqueous NaOH
Next, the intermediate product (P) reacts with aqueous NaOH. This reaction is a nucleophilic substitution where the bromine atom is replaced by a hydroxyl group (OH).

- The bromine atom is a good leaving group, and the hydroxide ion (OH⁻) from NaOH will attack the carbon atom bonded to the bromine, resulting in the formation of an alcohol.

**Intermediate Product (Q):** CH₃-CHOH-CH₃ (2-propanol)

### Step 3: Oxidation with K₂Cr₂O₇/H⁺
The final step involves the oxidation of the alcohol (Q) using potassium dichromate (K₂Cr₂O₇) in an acidic medium (H⁺).

- Secondary alcohols are oxidized to ketones. In this case, 2-propanol (Q) will be oxidized to acetone.

**Final Product (R):** CH₃-CO-CH₃ (acetone or propan-2-one)

### Summary of the Reaction Sequence
1. Propene (CH₃-CH=CH₂) + HBr → 2-bromopropane (P)
2. 2-bromopropane (P) + aq. NaOH → 2-propanol (Q)
3. 2-propanol (Q) + K₂Cr₂O₇/H⁺ → Acetone (R)

### Final Answer
The final product (Z) is acetone (CH₃-CO-CH₃).

---