Haloalkanes and Haloarenes — Class 12 Chemistry NCERT Solutions (Free)

Free step-by-step NCERT solutions for Class 12 Chemistry chapter "Haloalkanes and Haloarenes" — 9 important questions with detailed answers for CBSE board exam preparation.

TL;DR: Free step-by-step NCERT solutions for Class 12 Chemistry chapter "Haloalkanes and Haloarenes" — 9 important questions with detailed answers for CBSE b…

By Syllab.in · Updated

Key Questions Covered:

  1. What is the difference between haloalkanes and haloarenes? Give one example o…
  2. Explain the mechanism of nucleophilic substitution in alkyl halides. How does…
  3. Write the IUPAC name of CH3-CHBr-CH2-CH3.
  4. Explain the effect of the halogen atom on the reactivity of the benzene ring …
  5. Describe the Wurtz reaction. Write the equation for the reaction of CH3Br wit…
  6. What is the Finkelstein reaction? Explain with an example how it is used in t…
  7. + 3 more questions in the full chapter

Solutions Summary:

Question Status
What is the difference between haloalkanes and haloarenes… ✓ Solved
Explain the mechanism of nucleophilic substitution in alk… ✓ Solved
Write the IUPAC name of CH3-CHBr-CH2-CH3. ✓ Solved
Explain the effect of the halogen atom on the reactivity … ✓ Solved
Describe the Wurtz reaction. Write the equation for the r… ✓ Solved
What is the Finkelstein reaction? Explain with an example… ✓ Solved

Showing 6 of 9 questions

Q1: What is the difference between haloalkanes and haloarenes? Give one example of each.

Haloalkanes are compounds where halogen atoms are bonded to sp3 hybridized carbon atoms of alkane chains. Example: CH3CH2Br (bromoethane). Haloarenes are compounds where halogen atoms are bonded to sp2 hybridized carbon atoms of benzene rings. Example: C6H5Cl (chlorobenzene). Key difference: In haloalkanes, the C-X bond can undergo nucleophilic substitution easily. In haloarenes, the C-X bond is stronger due to partial double bond character from resonance, making nucleophilic substitution diff...

Q2: Explain the mechanism of nucleophilic substitution in alkyl halides. How does it differ from that in aryl halides?

In alkyl halides (haloalkanes): SN2 mechanism: Nucleophile attacks from the back side, opposite to the leaving group. This is a one-step process with inversion of configuration. Occurs with primary haloalkanes. SN1 mechanism: Forms carbocation intermediate, then nucleophile attacks. Two-step process with racemization. Occurs with tertiary haloalkanes. In aryl halides (haloarenes): Nucleophilic aromatic substitution is extremely slow under normal SN2/SN1 conditions because: - The C-X bond has p...

Q3: Write the IUPAC name of CH3-CHBr-CH2-CH3.

IUPAC name: 2-bromobutane Naming steps: 1. Main chain has 4 carbons = butane 2. Bromine (halogen) is the functional group at position 2 3. Numbering starts from the end nearest to the substituent to give the lowest number 4. Position 2 gives '2', position 3 would give '3', so position 2 is correct 5. Common name: sec-butyl bromide or secondary butyl bromide

Q4: Explain the effect of the halogen atom on the reactivity of the benzene ring in haloarenes. Why is chlorobenzene less reactive than benzene toward electrophilic substitution?

In haloarenes (e.g., chlorobenzene C6H5Cl): The halogen atom attached to the benzene ring is deactivating for electrophilic aromatic substitution despite being electron-donating by the inductive effect. Reason: - Halogens are electronegative (inductive effect: withdraw electron density) - Through resonance, halogens can donate electrons to the ring: lone pairs on halogen can form π bonds with the benzene ring - The resonance donation is weak because halogens are highly electronegative - Net ef...

Q5: Describe the Wurtz reaction. Write the equation for the reaction of CH3Br with Na in dry ether.

Wurtz reaction: Two alkyl halides react in the presence of sodium metal in dry ether to form an alkane with the union of the two alkyl groups. General equation: 2R-X + 2Na → R-R + 2NaX For CH3Br: 2 CH3Br + 2 Na → CH3-CH3 + 2 NaBr (bromoethane gives ethane) Mechanism: 1. R-X + Na → R-Na + NaX (formation of alkyl sodium, a very strong nucleophile) 2. R-Na + R-X → R-R + NaX (nucleophilic attack by R-Na on the other R-X) Limitations: When using two different alkyl halides (R-X and R'-X), a mixtu...

Q6: What is the Finkelstein reaction? Explain with an example how it is used in the lab.

Finkelstein reaction: An alkyl halide is converted to an alkyl iodide by reaction with sodium iodide (NaI) in dry acetone solvent. General equation: R-X + NaI → R-I + NaX Example: CH3Br + NaI → CH3I + NaBr (acetone solvent) Mechanism: This is an SN2 reaction. Iodide ion (I-) is an excellent nucleophile and attacks the alkyl halide, displacing the halide as a leaving group. Why acetone is used: - NaI is soluble in acetone - NaBr and NaCl (products) are insoluble in acetone and precipitate out...

Showing 6 of 9 questions. Visit the full page for complete solutions.

More Class 12 Chemistry NCERT Solutions