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 given question, we will analyze each step of the reaction sequence and identify the final product (Z).

### Step 1: Reaction of Propene with HBr
The starting compound is propene (CH₃-CH=CH₂). When HBr is added to propene, an electrophilic addition reaction occurs. According to Markovnikov's rule, the hydrogen atom from HBr will attach to the carbon with more hydrogen atoms (the terminal carbon), leading to the formation of a more stable carbocation.

1. **Identify the carbocation formation:**
- The hydrogen (H) will add to the terminal carbon (C1), creating a secondary carbocation at C2.
- The bromide ion (Br⁻) will then attack the secondary carbocation.

2. **Product Formation:**
- The product formed is 2-bromopropane (P), which has the structure CH₃-CHBr-CH₃.

### Step 2: Reaction of 2-bromopropane with aqueous NaOH
Next, the product 2-bromopropane (P) reacts with aqueous NaOH. This reaction is a nucleophilic substitution reaction (SN2 mechanism) where the hydroxide ion (OH⁻) acts as a nucleophile.

1. **Nucleophilic substitution:**
- The hydroxide ion (OH⁻) will attack the carbon atom bonded to bromine (C2), leading to the displacement of bromide ion (Br⁻).

2. **Product Formation:**
- The product formed is propan-2-ol (Q), which has the structure CH₃-CHOH-CH₃.

### Step 3: Oxidation of propan-2-ol with K₂Cr₂O₇ in acidic medium
The next step involves the oxidation of propan-2-ol (Q) using potassium dichromate (K₂Cr₂O₇) in an acidic medium.

1. **Oxidation Process:**
- K₂Cr₂O₇ is a strong oxidizing agent and will oxidize the secondary alcohol (propan-2-ol) to a ketone.

2. **Product Formation:**
- The final product (R) formed from this oxidation is acetone, which has the structure CH₃-CO-CH₃.

### Final Product (Z)
Thus, the final product (Z) after the sequence of reactions is acetone (R).

### Summary of the Steps:
1. Propene + HBr → 2-bromopropane (P)
2. 2-bromopropane + aq. NaOH → propan-2-ol (Q)
3. Propan-2-ol + K₂Cr₂O₇/H⁺ → acetone (R)

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

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