NEET · Chemistry · STD 12 - 6. Haloalkanes and Haloarenes

In the following reaction sequence, X and Z respectively are :
\( CH _3 CH _2 CH _2- OH + PCl _5 \longrightarrow CH _3 CH _2 CH _2 Cl +X+ HCl \)
\( CH _3 CH _2 CH _2 Cl \xrightarrow[\Delta]{\text { alc. } KOH } Y \xrightarrow[\left( C _6 H _5 CO \right)_2 O _2]{ HBr } Z\)

A \(X= POCl _3 ; Z= CH _3- CH ( Br )- CH _3\)
B \(X=POCl_3 ; Z=CH_3 CH_2 CH_2-Br\)
C \(X= H _3 PO _3 ; Z= CH _3- CH ( Br )- CH _3\)
D \(X= H _3 PO _3 ; Z= CH _3 CH _2 CH _2- Br\)

Verified Solution

Answer & Solution

Correct Answer

(B) \(X=POCl_3 ; Z=CH_3 CH_2 CH_2-Br\)

Step-by-step Solution

Detailed explanation

(B) \(X=POCl_3 ; Z=CH_3 CH_2 CH_2-Br\)
Reaction of primary alcohol with \(PCl _5\) gives alkyl chloride, \(POCl _3\), and HCl
\(CH_3 CH_2 CH_2 OH+PCl_5 \longrightarrow CH_3 CH_2 CH_2 Cl+POCl_3+HCl\)
Thus, \(X= POCl _3\).
Dehydrohalogenation of 1-chloropropane with alcoholic KOH yields propene.
\(CH_3 CH_2 CH_2 Cl \xrightarrow{\text { alc. } KOH, \Delta} CH_3 CH=CH_2\)
Thus, \(Y= CH _3 CH = CH _2\).
Addition of HBr to propene in the presence of peroxide follows anti-Markovnikov addition.
\(CH_3 CH=CH_2+HBr \xrightarrow{\left(C_6 H_5 CO\right)_2 O_2} CH_3 CH_2 CH_2 Br\)
Thus, \(Z= CH _3 CH _2 CH _2 Br\).

Apply the relevant identity from the chapter and substitute the values established in the previous step, keeping the original constraint in view.

Use the simplified expression to isolate the unknown, then plug the result back into the question setup to confirm the working is internally consistent.

Cross-check against a boundary or limiting case. Both the dimensional balance and the qualitative behaviour at the extreme should agree with the candidate answer.

Combine the steps above to identify the correct option. The remaining choices each fail at least one of the consistency, dimensional, or boundary checks.

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Match List I with List II:

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(b) Euchromatin	(ii) Densely packed and dark-stained
(c) Frederick Griffith	(iii) Loosely packed and light-stained
(d) Heterochromatin	(iv) DNA as genetic material confirmation

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In the following reaction sequence, X and Z respectively are :\( CH _3 CH _2 CH _2- OH + PCl _5 \longrightarrow CH _3 CH _2 CH _2 Cl +X+ HCl \)\( CH _3 CH _2 CH _2 Cl \xrightarrow[\Delta]{\text { alc. } KOH } Y \xrightarrow[\left( C _6 H _5 CO \right)_2 O _2]{ HBr } Z\)

Step-by-step Solution

In the following reaction sequence, X and Z respectively are :
\( CH _3 CH _2 CH _2- OH + PCl _5 \longrightarrow CH _3 CH _2 CH _2 Cl +X+ HCl \)
\( CH _3 CH _2 CH _2 Cl \xrightarrow[\Delta]{\text { alc. } KOH } Y \xrightarrow[\left( C _6 H _5 CO \right)_2 O _2]{ HBr } Z\)