Haloalkanes/Halogenalkanes

Question 1

What are the three types of haloalkanes?

Answer 1

Primary
Secondary
Tertiary

Question 2

Describe the Carbon-Halogen bond in haloalkanes.

Answer 2

The Carbon-Halogen bond is polar because halogens are more electronegative than Carbon.

Question 3

Describe the reactivity between C-I, C-Br, C-Cl and C-F.

Answer 3

Reactivity increases: C-F < C-Cl < C-Br < C-I
Bond breaks more easily the more reactive the Carbon-Halogen bond is.

Question 4

Define nucleophile.

Answer 4

Has a lone pair of electrons
Attracted to positive charge

Question 5

Describe the two types of nucleophilic substitution.

Answer 5

Sn1:
Takes place in 2 steps
Via carbocation intermediate
Only in secondary and tertiary haloalkanes

Sn2:
Takes place in 1 step
Includes transition state
Only in primary and secondary haloalkanes

Question 6

Describe the mechanisms of the two types of nucleophilic substitution.

Answer 6

Sn1:
Step 1 - Haloalkane ionises to form carbocation
Step 2 - Nucleophilic attack

Sn2:
Step 1 - Nucleophilic attack

Question 7

Describe the reagents and conditions for the nucleophilic substitution of hydroxide ions.

Answer 7

Reagents: NaOH or KOH

Dilute NaOH (aq)
Product: Alcohol
Type of reaction: Nucleophilic Substitution Sn1
Conditions: Heat under reflux (i.e. heating with a condenser placed vertically reaction flask to prevent loss of volatile substance
Example: CH3C(CH3)2Br + NaOH -> CH3C(CH3)2OH + NaBr

Ethanolic NaOH <- dissolved in ethanol
Exception -> this is an ELIMINATION reaction
Product: Alkene
Conditions: Heat
Example: CH3CH2Br + NaOH -> CH2=CH2 + NaBr + H2O

Question 8

Describe the reagents and conditions for the nucleophilic substitution of cyanide ions.

Answer 8

Reagents: NaCN, H+ (acidified sodium cyanide)
Type of reaction: Nucleophilic Substitution Sn1
Conditions: Heat under reflux, ethanol as solvent

Question 9

Describe the hydrolysis of nitriles.

Answer 9

The nitrile can be converted into a carboxylic acid
Heat with dilute HCl/H2SO4
Example: CH3CH2CN + 2H2O + HCl -> CH3CH2COOH + NH4Cl

Question 10

Describe the reagents and conditions for the nucleophilic substitution of ammonia.

Answer 10

Conditions: Heat under pressure, ethanol as solvent
Type of reaction: Nucleophilic Substitution Sn1 or Sn2
Example:
Sn2: CH3CH2Br + 2NH3 -> CH3CH2NH2 (amine) + NH4Br
Sn1: CH3C(CH3)2Br -> CH3C(CH3)2NH2 + NH4Br