Topic 18

Question 1

Bromination of benzene

Answer 1

Reactants: benzene, bromine
Reagents: FeBr3 or AlCl3 catalyst
Conditions:
Products: bromobenzene, HBr
Observations: orange to colourless
                         HBr + ammonia = white solid
Reaction: Electrophilic substitution

Question 2

Nitration of benzene

Answer 2

Reactants: benzene, nitric acid
Reagents: concentrated sulfuric acid
Conditions: 50°C
Products: nitrobenzene, water
Observations: nitrobenzene is yellow and oily
Reaction: Electrophilic substitution

Question 3

Friedel-Crafts alkylation of benzene

Answer 3

Reactants: benzene, halogenoalkane
Reagents: AlCl3 catalyst
Conditions: anhydrous, heat under reflux
Products: eg. methyl benzene, HCl
Observations: HCl = misty fumes
Reaction: Electrophilic substitution

Question 4

Friedel-Crafts acylation of benzene

Answer 4

Reactants: benzene, acyl chloride
Reagents: AlCl3 catalyst
Conditions: anhydrous, heat under reflux
Products: phenyl ketone, HCl
Observations: HCl = misty fumes
Reaction: Electrophilic substitution

Question 5

Phenol + sodium hydroxide

Answer 5

Sodium phenoxide and water

Acting as an acid

Question 6

Bromination of phenol

Answer 6

Reactants: phenol, bromine
Reagents: no catalyst needed
Conditions: room temp
Products: 2,4,6 tribromophenol, HBr
Observations: orange to colourless, white ppt, misty fumes
Reaction: Electrophilic substitution

Question 7

Making amines from halogenoalkanes

Answer 7

Reactants: halogenoalkane, ammonia
Reagents: 
Conditions: heat in a sealed tube
Products: 1° amine, HCl
Observations: HCl = misty fumes
Reaction: Nucleophilic substitution

Note: 1° amine reacts with halogenoalkane forming 2° amine and HCl etc.

Question 8

Making amines from nitriles

Answer 8

Reactants: eg. ethanenitrile
Reagents: LiAlH4
Conditions: mix in dry ether
Products: 1° amine
Observations:
Reaction: reduction of nitrile

Question 9

Making aromatic amines

Answer 9

Reactants: nitrobenzene
Reagents: tin metal mixed with conc. hydrochloric acid (reducing agent, 6Hs)
Conditions: heat under reflux
Products: phenylamine and 2 water
Observations: 
Reaction: reduction of nitrobenzene

Question 10

Making amides

Answer 10

Reactants: acyl chloride or carboxylic acid, amine
Reagents:
Conditions:
Products: N-substituted amide, HCl or water
Observations: amine also reacts with HCl formed = white smoke
Reaction: condensation

Question 11

Order of basicity of amines

Answer 11

Least basic
Aromatic amines- The lone pair on the N atom in phenylamine merges with the delocalised electrons in the pi bond, making them less available for donating.
Ammonia
1°/2°/3° amines- The ethyl group is electron releasing, so the N atom has a higher electron density, so the lone pair is more available.

Question 12

Reaction of 1° amine with water

Answer 12

RNH₂ + H₂O ⇌ RNH₃⁺+ OH‾

Question 13

Reaction of 1° amine with acid

Answer 13

RNH₂ + HCl ⇌ RNH₃⁺Cl‾ (white smoke)

Question 14

Reaction of 1° amine with acid

Answer 14

RNH₂ + HCl (g) ⇌ RNH₃⁺Cl‾ (white smoke)

Question 15

Reaction of 1° amine with copper (II) ions

Answer 15

2RNH₂ + [Cu(H₂O)₆]²⁺ ⇌ [Cu(H₂O)₄(OH)₂] + 2 RNH₃⁺
Pale blue precipitate
4RNH₂ + [Cu(H₂O)₄(OH)₂] ⇌ [Cu(RNH₂)₄(H₂O)₂]²⁺ + 2H₂O + 2OH‾
Deep blue solution

Question 16

Reaction of 1° amine with acyl chloride

Answer 16

Acyl chloride + primary amine → N-substituted amide + HCl

then HCl + RNH₂ (primary amine) → RNH₃⁺Cl‾ (salt)

Question 17

Reaction of 1° amine with halogenoalkane

Answer 17

1° amine + halogenoalkane → 2° amine + HCl
2° amine + halogenoalkane → 3° amine + HCl
3° amine + halogenoalkane → 4° amine⁺ Cl‾

Question 18

Why are amino acids soluble?

Answer 18

They form zwitter ions, which interact with the water

Question 19

Why do solid amino acids have a high melting point?

Answer 19

They form zwitter ions with strong ionic bonds

Question 20

Why is phenol more reactive than benzene with bromine?

Answer 20

The lone pair of electrons on the oxygen merges with the delocalised system
Increases the electron density of the ring
Increases the susceptibility to attack by the electrophile

Question 21

Why heat under reflux

Answer 21

Speed up rate of reaction

Prevent loss of volatile reactants and products

Question 22

What do alcohols, phenols and carboxylic acids react with as acids?

Answer 22

Alcohol- metal
Phenol- metal and hydroxides
Carboxylic acid- metal, hydroxides and carbonates

Question 23

Describe the structure of benzene and compare it to the kekule structure.

Answer 23

P orbitals overlap sideways forming a pi bond above and below the plane of C atoms.
The pi bond electrons are delocalised around the ring.
Bonding more stable.

Question 24

What is the trend in boiling points of primary to tertiary amines?

Answer 24

1- highest
2- lower, N atom in middle of chain, dipole attractions less
3- no H atoms bonded to N atoms, no H bonds!

Question 25

Define zwitterion

Answer 25

A molecule containing positive and negative charges but has no overall charge

Question 26

What is the isoelectronic point?

Answer 26

The pH of a an aqueous solution at which it is electrically neutral.

Question 27

Hydrolysis of dipeptides

Answer 27

Reactants: Dipeptide and water
Conditions: Heat with conc. HCl
Products: 2 amino acids
Observations: forms protonated version of amino acids