3 - Halogenoalkanes

Question 1

What 2 reactions can halogenoalkanes undergo?

Answer 1

• Nucleophilic substitution
• Elimination

Question 2

Halogenoalkanes can undergo certain reactions. Which halogenoalkane reacts the fastest and why?

Answer 2

Iodoalkanes react the fastest
- This is due to the carbon-iodine bond being the weakest, requiring the least amount of energy to break

Question 3

Are carbon-halogen bonds in halogenoalkanes polar or non-polar? Why?

Answer 3

Polar
- The halogen atom is more electronegative than the carbon atom
- Therefore, the carbon atom will be slightly positive and the halogen atom will be slightly negative

Question 4

What is nucleophilic substitution?

Answer 4

Where a nucleophile substitutes for a halogen in a halogenoalkane to change the functional group

Question 5

What is a nucleophile?

Answer 5

An atom or a group of atoms which is attracted to an electron deficient atom that donates a pair of electrons

Question 6

Why are carbon atoms in a carbon-halogen bond in halogenoalkane susceptible to nucleophilic substitution?

Answer 6

The carbon is electron deficient (partially positive) and nucleophiles are attracted to electron defiecient atoms and will donate its electron pair to the carbon atom

Question 7

List the 3 nucleophiles

Answer 7

• Hydroxide ions (OH^-)
• Cyanide ions (CN^-)
• Ammonia (NH₃)

Question 8

What are the conditions and reagents for the nucleophilic substitution of halogenoalkanes with hydroxide ions?

Answer 8

Conditions: In aqueous solution, warm
Reagent: Potassium or sodium hydroxide

Question 9

What change in functional group is observed when a halogenalkane undergos nucleophilic substitution with hydroxide ions?

Answer 9

Halogenoalkane → alcohol

Question 10

What are the conditions and reagents for the nucleophilic substitution of halogenoalkanes with cyanide ions?

Answer 10

Conditions: Heat under reflux
Reagent: Sodium cyanide dissolved in an ethanol and water misture

Question 11

What change in functional group is observed when a halogenalkane undergos nucleophilic substitution with cyanide ions?

Answer 11

Halogenoalkane → nitrile

Question 12

What are the conditions and reagents for the nucleophilic substitution of halogenoalkanes with ammonia?

Answer 12

Conditions: Heating under pressure
Reagent: Ammonia dissolved in excess ethanol

Question 13

What change in functional group is observed when a halogenalkane undergos nucleophilic substitution with ammonia?

Answer 13

Halogenoalkane → amine

Question 14

What does an elimination reaction in halogenoalkanes form?

Answer 14

An alkene

Question 15

What are the conditions and reagents for the elimination of halogenoalkanes?

Answer 15

Conditions: In ethanol, heated
Reagent: ethanolic potassium/sodium hydroxide

Question 16

What type of reagent is ethanolic sodium/potassium hydroxide?

Answer 16

A base

Question 17

Halogenoalkanes can undergo either nucleophilic substitution or elimination depending on the choice of solvent. What reaction is favoured in aqueous solutions?

Answer 17

Nucleophilic substitution
- OH^- acts as a nucleophile

Question 18

Halogenoalkanes can undergo either nucleophilic substitution or elimination depending on the choice of solvent. What reaction is favoured in ethanolic solutions?

Answer 18

Elimination
- OH^- acts as a base

Question 19

When using a solvent mixture of both water and alcohol with hydroxide ions and halogenoalkanes, what occurs?

Answer 19

Both nucelophilic substitution and elimination will occur, giving a mixture of alcohols and alkenes