Chapter Exam

Chapter-6 Haloalkanes and Haloarenes — Online MCQ Test

Q: What is the IUPAC name of CH₃-CHBr-CH₂-CH₃?

Answer: A. 2-bromobutane — The longest carbon chain has 4 atoms, and Br is at position 2 when numbering from the end nearest to the halogen.

Q: Which of the following is a haloalkane?

Answer: B. Chloroethane — Haloalkanes contain halogen bonded to sp³ hybridized carbon. Chloroethane (C₂H₅Cl) is a haloalkane, while others are haloarenes.

Q: The formula of a haloalkane with 3 carbon atoms and one chlorine is:

Answer: A. C₃H₇Cl — For alkane CₙH₂ₙ₊₂, a 3-carbon alkane is C₃H₈. Replacing one H with Cl gives C₃H₇Cl.

Q: What is the correct IUPAC name for (CH₃)₃C-Br?

Answer: B. 2-bromo-2-methylpropane — The structure is a 3-carbon chain with Br and CH₃ both at position 2 (the central carbon), giving 2-bromo-2-methylpropane.

Q: Which factor does NOT affect the rate of SN2 reaction?

Answer: D. Concentration of leaving group only — SN2 rate depends on both substrate and nucleophile concentrations. Leaving group concentration alone doesn't significantly affect rate in typical conditions.

Q: In aqueous solution, (CH₃)₃C-Br undergoes hydrolysis to form (CH₃)₃C-OH. Which mechanism operates here?

Answer: B. SN1 — Tertiary haloalkane undergoes hydrolysis via SN1 mechanism because tertiary carbocation is relatively stable.

CHEMISTRY · Grade 12 · CBSE(NCERT)

Practice Chapter-6 Haloalkanes and Haloarenes with a free chapter-wise online MCQ test for CBSE(NCERT) Grade 12 CHEMISTRY. This chapter covers: nomenclature - SN1 mechanism - SN2 mechanism - chemical reactions. AI-generated questions from basic to board-exam level, with instant results and explanations.

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Chapter-6 Haloalkanes and Haloarenes — Important Questions & Answers (FAQ)

Frequently asked questions from CBSE(NCERT) Grade 12 CHEMISTRY — Chapter-6 Haloalkanes and Haloarenes, with answers and explanations. These are sample questions; the exam has its own separate question set.

What is the IUPAC name of CH₃-CHBr-CH₂-CH₃?

A. 2-bromobutane ✓
B. 1-bromobutane
C. 3-bromobutane
D. 2-bromopropane

Answer: A. 2-bromobutane
The longest carbon chain has 4 atoms, and Br is at position 2 when numbering from the end nearest to the halogen.

Which of the following is a haloalkane?

A. Chlorobenzene
B. Chloroethane ✓
C. Bromobenzene
D. Iodobenzene

Answer: B. Chloroethane
Haloalkanes contain halogen bonded to sp³ hybridized carbon. Chloroethane (C₂H₅Cl) is a haloalkane, while others are haloarenes.

The formula of a haloalkane with 3 carbon atoms and one chlorine is:

A. C₃H₇Cl ✓
B. C₃H₆Cl
C. C₃H₈Cl
D. C₃H₅Cl

Answer: A. C₃H₇Cl
For alkane CₙH₂ₙ₊₂, a 3-carbon alkane is C₃H₈. Replacing one H with Cl gives C₃H₇Cl.

What is the correct IUPAC name for (CH₃)₃C-Br?

A. 3-bromo-3-methylpropane
B. 2-bromo-2-methylpropane ✓
C. 1-bromo-1-methylpropane
D. tert-butyl bromide

Answer: B. 2-bromo-2-methylpropane
The structure is a 3-carbon chain with Br and CH₃ both at position 2 (the central carbon), giving 2-bromo-2-methylpropane.

Which factor does NOT affect the rate of SN2 reaction?

A. Concentration of nucleophile
B. Nature of solvent
C. Temperature
D. Concentration of leaving group only ✓

Answer: D. Concentration of leaving group only
SN2 rate depends on both substrate and nucleophile concentrations. Leaving group concentration alone doesn't significantly affect rate in typical conditions.

In aqueous solution, (CH₃)₃C-Br undergoes hydrolysis to form (CH₃)₃C-OH. Which mechanism operates here?

A. SN2
B. SN1 ✓
C. E1
D. E2

Answer: B. SN1
Tertiary haloalkane undergoes hydrolysis via SN1 mechanism because tertiary carbocation is relatively stable.

Why does 1-bromo-2-methylpropane NOT undergo SN2 reaction readily?

A. Because the carbon bearing Br is primary
B. Because the nearby methyl group causes severe steric hindrance (neopentyl system) ✓
C. Because Br is a poor leaving group
D. Because primary carbocations are unstable

Answer: B. Because the nearby methyl group causes severe steric hindrance (neopentyl system)
Despite being primary, the neopentyl structure has a bulky tert-butyl-like hindrance from the adjacent isopropyl group, blocking nucleophilic backside attack.

Consider the reaction: R-Br + NaI → R-I + NaBr (Finkelstein reaction). Why is this reaction driven forward in acetone?

A. NaI is more reactive than NaBr
B. I⁻ is a better nucleophile than Br⁻ in acetone
C. R-I is less soluble/NaBr is more soluble in acetone, shifting equilibrium ✓
D. Both a and b

Answer: C. R-I is less soluble/NaBr is more soluble in acetone, shifting equilibrium
NaBr is more soluble in acetone and precipitates out, while R-I remains soluble, driving the SN2 reaction forward.

In the reaction of optically active (S)-2-iodooctane with KCN in DMSO via SN2 mechanism, what is the stereochemical outcome?

A. Retention of S configuration
B. Inversion to R configuration with high optical purity ✓
C. Racemic mixture of R and S
D. S configuration is maintained with loss of optical activity

Answer: B. Inversion to R configuration with high optical purity
SN2 proceeds with Walden inversion. (S)-2-iodooctane inverts to give (R)-2-cyanooctane with high stereochemical purity.

Compound A (sec-butyl chloride) is dissolved in water containing ¹⁸OH. After the reaction, the ¹⁸O label is found in the product. What mechanism predominantly operates, and what is the evidence?

A. SN2, because ¹⁸O directly attacks from backside
B. SN1, because ¹⁸O can attack both faces of carbocation intermediate equally ✓
C. E1, because labeled water attacks the carbocation π-system
D. SN2, because water solvates the leaving group

Answer: B. SN1, because ¹⁸O can attack both faces of carbocation intermediate equally
Presence of ¹⁸O in product indicates nucleophilic water attack. In aqueous solution with secondary halide, SN1 carbocation pathway operates with water attacking from both faces.

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