Nature of C-X Bond - UNSOLVED PRACTICE SET
Chapter: Haloalkanes and Haloarenes | Topic: Nature of C-X Bond
NATURE OF C-X BOND - UNSOLVED PRACTICE SET
Topic: Nature of C-X Bond
Multiple Choice Questions
Q1. The C–X bond in haloalkanes is:1. The C–X bond in haloalkanes is:
- Non-polar covalent
- Polar covalent
- Ionic
- Coordinate
Q2. The bond length of C–X bond increases in the order:
- C–Cl < C–Br < C–I
- C–I < C–Br < C–Cl
- C–Br < C–Cl < C–I
- C–Cl < C–I < C–Br
Q3. The bond dissociation energy of C–X bond decreases in the order:
- C–F > C–Cl > C–Br > C–I
- C–I > C–Br > C–Cl > C–F
- C–Cl > C–F > C–Br > C–I
- C–F > C–Br > C–Cl > C–I
Q4. The C–X bond in haloarenes is shorter and stronger than in haloalkanes because of:
- Resonance
- Inductive effect
- Hyperconjugation
- Steric hindrance
Q5. The dipole moment of CH₃Cl is greater than that of CH₃F because:
- Chlorine is more electronegative than fluorine
- The C–Cl bond length is larger than C–F bond length
- Chlorine has more electrons than fluorine
- Both (b) and (c)
Q6. The bond energy of C–F bond is highest among C–X bonds because:
- Fluorine is most electronegative
- The bond is shortest due to small size of fluorine
- There is partial double bond character
- Both (a) and (b)
Short Answer Questions
Q7. Explain why the C–Cl bond in chlorobenzene is shorter than in CH₃Cl.
Q8. The dipole moment of CCl₄ is zero despite having four polar C–Cl bonds. Explain why.
Q9. Arrange the following in order of increasing bond length: C–F, C–Cl, C–Br, C–I. Explain the trend based on atomic size.
Q10. Why is the C–X bond in vinyl chloride (CH₂=CHCl) shorter than in ethyl chloride (CH₃CH₂Cl)?
Q11. Explain why the bond dissociation energy of C–Br bond is less than that of C–Cl bond.
Q12. The C–X bond in haloarenes is less polar than in haloalkanes. Explain this observation.
Long Answer Questions
Q13. (a) Describe the nature of the C–X bond in haloalkanes. Why is it polar?
(b) Explain the trends in:
(i) Bond length
(ii) Bond dissociation energy
(iii) Bond polarity
for C–F, C–Cl, C–Br, and C–I bonds.
(c) Why does the reactivity of haloalkanes increase from C–F to C–I?
Q14. (a) Explain the nature of the C–X bond in haloarenes. How does it differ from that in haloalkanes?
(b) Discuss the resonance structures of chlorobenzene. How does resonance affect:
(i) The C–Cl bond length
(ii) The C–Cl bond strength
(iii) The reactivity of chlorobenzene towards nucleophilic substitution
(c) Why is chlorobenzene less reactive than alkyl halides towards nucleophilic substitution?
Q15. (a) Compare the C–X bond in the following compounds:
CH₃CH₂Cl (ethyl chloride)
CH₂=CHCl (vinyl chloride)
C₆H₅Cl (chlorobenzene)
CH₂=CHCH₂Cl (allyl chloride)
Discuss the bond length, bond strength, and polarity in each case.
(b) Explain the order of reactivity towards nucleophilic substitution for these compounds.
Numerical / Application-Based Problems
Q16. The following table gives bond energy and bond length data for C–X bonds:
| Bond | Bond Energy (kJ/mol) | Bond Length (pm) |
|---|---|---|
| C–F | 485 | 139 |
| C–Cl | 339 | 177 |
| C–Br | 285 | 194 |
| C–I | 218 | 213 |
(a) Plot graphs of bond energy vs. bond length and bond energy vs. halogen atomic number.
(b) What trend do you observe? Explain the trend in terms of atomic size and electronegativity.
(c) Calculate the percentage decrease in bond energy from C–F to C–I.
(d) The C–F bond has the highest bond energy but alkyl fluorides are the most reactive haloalkanes. Explain this apparent contradiction.
(e) A chemist needs to choose a halogen for a reaction where the C–X bond must be easily broken. Which halogen would you recommend and why?
Q17. The dipole moments of some methyl halides are given below:
| Compound | Dipole Moment (D) |
|---|---|
| CH₃F | 1.82 |
| CH₃Cl | 1.94 |
| CH₃Br | 1.79 |
| CH₃I | 1.64 |
(a) Why does CH₃Cl have a higher dipole moment than CH₃F despite fluorine being more electronegative?
(b) Explain the decreasing trend in dipole moment from CH₃Cl to CH₃I.
(c) Calculate the ionic character percentage of the C–Cl bond if the calculated dipole moment for complete ionic character is 6.1 D.
(d) The dipole moment of CHCl₃ is 1.15 D while that of CCl₄ is 0 D. Explain this difference.
(e) A student claims that CF₄ should have a higher dipole moment than CH₃F because it has four C–F bonds. Is this correct? Explain.
Q18. In a school science project, students investigate the properties of CFCs (chlorofluorocarbons) and their environmental impact.
(a) The C–Cl bond in CFCs is weaker than the C–F bond. Explain why this is important for the breakdown of CFCs in the upper atmosphere.
(b) When CFCs reach the stratosphere, UV light breaks the C–Cl bond. Write the reaction showing the formation of chlorine radicals.
(c) These chlorine radicals catalyze the destruction of ozone (O₃). Write the catalytic cycle showing how one Cl radical can destroy many ozone molecules.
(d) Why are hydrofluorocarbons (HFCs) considered better alternatives to CFCs, even though they also contain C–F bonds?
(e) The Montreal Protocol (1987) phased out CFCs. Why was this international agreement necessary? What would happen if CFCs continued to be used?