Module 4 - Haloalkanes

Question 1

What is a haloalkane?

Answer 1

A haloalkane is an alkane with at least one halogen atom (F, Cl, Br, I) replacing a hydrogen atom.

Question 2

What is the general formula of a haloalkane?

Answer 2

CₙH₂ₙ₊₁X, where X is a halogen.

Question 3

How are haloalkanes named?

Answer 3

Prefix ( floro-, chloro-, bromo-, iodo- ) + longest carbon chain + number position of halogen.
Example, 1-chloropropane or 2-bromobutane

Question 4

What determines the reactivity of haloalkanes?

Answer 4

C-X Bond Strength (bond enthalpy) & C-X Bond Polarity

• Weaker bonds (e.g., C-I) = More reactive
• More polar bonds (e.g., C-F) = Stronger but less reactive

Question 5

What is nucleophilic substitution?

Answer 5

A reaction where a nucleophile (electron pair donor) replaces the halogen in a haloalkane.

Question 6

Examples of nucleophiles in haloalkane reactions?

Answer 6

OH⁻, CN⁻, NH₃ (hydroxide, cyanide, ammonia)

Question 7

Hydrolysis of haloalkanes

Answer 7

Reaction:
Haloalkane + OH⁻ → Alcohol + Halide ion
(e.g., C₂H₅Br + OH⁻ → C₂H₅OH + Br⁻)

Question 8

Rate of hydrolysis: which halogen is fastest?

Answer 8

Fastest → Iodine (C-I weakest bond)
Slowest → Fluorine (C-F strongest bond)

Question 9

How can we trust for haloalkanes?

Answer 9

White ppt = AgCl
Cream ppt = AgBr
Yellow ppt = AgI

Question 10

What are CFCs? Why are they harmful?

Answer 10

• Chlorofluorocarbons (CFCs) → Non-reactive haloalkanes used in aerosols/refrigerants.
• Harmful → They break down ozone (O₃), forming oxygen (O₂), which reduces ozone layer protection.

Question 11

Ozone depletion: key reaction steps

Answer 11

• Initiation:
  → CCl₃F → •CCl₂F + Cl• (UV breaks C-Cl bond)
• Propagation:
  → Cl• + O₃ → ClO• + O₂
  → ClO• + O → Cl• + O₂
• Overall Reaction:
  → O₃ + O → 2O₂ (ozone destroyed)

Question 12

Alternatives of CFCs?

Answer 12

HCFCs & HFCs (less harmful) and hydrocarbons