Question

A hydrocarbon 'P' (\(C_4H_8\)) on reaction with HCl gives an optically active compound 'Q' (\(C_4H_9Cl\)) which on reaction with one mole of ammonia gives compound 'R' (\(C_4H_{11}N\)). 'R' on diazotization followed by hydrolysis gives 'S'. Identify P, Q, R and S.

• A. \(P=CH_3-CH_2-CH=CH_2\), \(Q=CH_3-CH_2-CH_2-CH_2Cl\), \(R=CH_3-CH_2-CH_2-NH_2\), \(S=CH_3-CH_2-CH(OH)CH_3\)
• B. \(P=CH_3-CH=CH-CH_3\), \(Q=CH_3-CH_2-CH_2-CH_2-Cl\), \(R=CH_3-CH_2-CH(NH_2)CH_3\), \(S=CH_3-CH_2-CH_2-CH_2OH\)
• C. \(P=CH_3-CH=CH-CH_3\), \(Q=CH_3-CH_2-CH(Cl)CH_3\), \(R=CH_3-CH_2-CH(NH_2)CH_3\), \(S=CH_3-CH_2-CH(OH)CH_3\)
• D. P=Cyclobutane, Q=Chlorocyclobutane, R=Cyclobutylamine, S=Cyclobutanol

Hint:

In multi-step organic synthesis problems, use key information like "optically active" to eliminate possibilities early on. Working forwards or backwards through the reaction sequence can help confirm the structure of all intermediates. Remember the stereochemical implications of reactions.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:

A hydrocarbon P with molecular formula C₄H₈ undergoes a sequence of reactions to form compounds Q, R, and S. A crucial clue is that compound Q is optically active, which means it must contain a chiral carbon atom. Using this information, we deduce the structures step by step.

Step 2: Detailed Explanation:

Reaction 1: P (C₄H₈) + HCl → Q (C₄H₉Cl, optically active)

Compound P is an alkene. Possible isomers of C₄H₈ are: But-1-ene, But-2-ene (cis/trans), and 2-methylpropene.

For the product Q to be optically active, it must have a chiral carbon (a carbon attached to four different groups).

Addition of HCl to the alkenes gives:
• But-1-ene + HCl → mainly 2-chlorobutane (chiral) • But-2-ene + HCl → 2-chlorobutane (chiral) • 2-Methylpropene + HCl → tert-butyl chloride (achiral)

Thus, P cannot be 2-methylpropene. So, P is either But-1-ene or But-2-ene, and Q is 2-chlorobutane (CH₃CH₂CH(Cl)CH₃).

Reaction 2: Q + NH₃ → R (C₄H₁₁N)

This is an ammonolysis (nucleophilic substitution) reaction in which the chlorine atom is replaced by an amino group.

2-Chlorobutane + NH₃ → Butan-2-amine
Structure of R: CH₃CH₂CH(NH₂)CH₃

Reaction 3: R → S (Diazotization followed by hydrolysis)

Diazotization of a primary aliphatic amine using nitrous acid results in replacement of the –NH₂ group by –OH.

Butan-2-amine → Butan-2-ol
Structure of S: CH₃CH₂CH(OH)CH₃

Step 3: Matching with Options:

The deduced sequence is:
P = But-2-ene (or But-1-ene) Q = 2-Chlorobutane R = Butan-2-amine S = Butan-2-ol

Among the given options, only Option (C) correctly represents this complete reaction sequence.

Final Answer:

The correct option is (C).