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A Level Organic Chemistry > Section 6 - Aromatic Compounds and Amines > Flashcards

Section 6 - Aromatic Compounds and Amines Flashcards

1
Q

What is the formula for benzene?

A

C6H6

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2
Q

What is the structure of benzene?

A

Planar cyclic:

  • each carbon atom forms a covalent bond to two other carbons and one hydrogen atom
  • the unpaired electron is located in a p-orbital that sticks out above and below the plane of the ring
  • these orbitals all combine to make a ring of delocalised electrons - pi bond.
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3
Q

Does the pi bond make benzene stable or unstable?

A

Stable

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4
Q

Describe the stability of benzene in relation to theoretical cyclohexa-1,3,5-triene:

A
  • cyclohexene has one double bond and an enthalpy change of -120kJmol-1 when hydrogenated.
  • we would expect cyclohexatriene to have an enthalpy change of -360kJmol-1.
  • the experimental enthalpy change of benzene is -208kJmol-1 suggesting its bonds are harder to break than cyclohexatriene.
  • benzene is much more stable - probably because of the pi bonds.
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5
Q

What kind of reactions do arenes undergo?

A

Electrophilic Substitution

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6
Q

Why is the benzene ring so good at attracting electrophiles?

A

Because of the high electron density of the pi bond.

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7
Q

Why doesn’t benzene undergo electrophilic addition reactions?

A

This would destroy the ring of delocalised electrons.

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8
Q

How reactive is benzene?

A

Fairly unreactive - it’s so stable

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9
Q

What is a halogen carrier?

A

A catalyst used to make electrophiles stronger.

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10
Q

Give an example of a halogen carrier:

A

AlCl3

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11
Q

How does AlCl3 make the acyl chloride electrophile stronger?

A
  • it accepts a lone pair from the acyl chloride
  • as the lone pair is pulled away, the polarisation of the acyl chloride increases and a carbocation forms (C+)
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12
Q

What are the conditions for Friedel-Crafts Acylation?

A
  • heat
  • reflux
  • non-aqueous solvent
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13
Q

What are the conditions for nitration of benzene?

A
  • conc sulfuric acid
  • conc nitric acid
  • 50oc (for only 1 NO2)
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14
Q

What are the equations for the formation of the nitronium ion in nitration of benzene?

A

HNO3 + H2SO4 —> H2NO3+ + HSO4-

H2NO3+ —> NO2+ + H2O

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15
Q

Why are aromatic amines useful?

A

Used to manufacture dyes and pharmaceuticals

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16
Q

How can aromtic amines be formed from nitro compounds?

A

Reduction

17
Q

What is the IUPAC name for TNT?

A

trinitrotolouene

18
Q

What are amines?

A

Organic derivatives of ammonia

19
Q

Why are quaternary ammonium salts used as cationic surfactants?

A
  • The hydrocarbon tale binds to non-polar substances like grease
  • The cationic head will dissolve in water
  • The ammonium ion can also bind to negatively charged sufraces like hair and fibre to prevent static.
20
Q

Are amines acidic or basic? Why?

A

Basic - they accept protons.

21
Q

What kind of bond can the lone pair of the electrons on the ntrogen atom form with a H+ ion?

A

A dative covalent bond

22
Q

What determines the strength of an amine as a base?

A

The availability of the lone pair of electrons on the Nitrogen atom.

23
Q

Why are primary amines more basic than ammonia?

A
  • Alkyl group has a positive inductive effect towards the Nitrogen atom
  • Lone pair becomes more available
24
Q

Why is ammonia more basic than phenylamine?

A
  • The lone pair on the Nitrogen atom merge with the delocalised cloud of electrons.
  • The lone pair is less available.
25
Q

Are amines electrophiles or nucleophiles?

A

Nucleophiles

26
Q

What is the mechanism for the reaction of ammonia and halogenoalkanes?

A

Nucleophilic Substitution

27
Q

What is the product of the reaction of ammonia with halogenoalkanes?

A

A mixture of primary, secondary and tertiary amines and quaternary ammonium salt.

28
Q

Why is the product of heating halogenoalkanes with ammonia a mixture?

A

The primary amine you first produce can react with other remaining halogenoalkane in a nucleophilic substitution reaction.

29
Q

What are the conditions of the reaction between halogenoalkanes and ammonia?

A
  • heat
  • excess ammonia
30
Q

What is an apropriate lab method of reducing a nitrile to make a primary amine?

A
  • Lithium Aluminium Hydride (LiAlH4) - a strong reducing agent
  • Non-aqueous solvent (eg. dry ether)
  • Dilute acid
31
Q

Why is LiAlH4 inapropriate for industrial reduction of nitriles?

A

Too expensive

32
Q

What is an apropriate industrial method of reducing nitriles?

A

Catalytic Hydrogenation

  • hydrogen gas
  • metal catalyst (platinum or nickel)
  • high temp and pressure
33
Q

How do you make aromatic amines?

A

Reduction of a nitro-compound e.g. nitrobenzene

34
Q

What are the conditions for the reduction of nitrobenzene?

A

1) - heat
- tin metal
- concentrated HCl
- reflux

(makes a salt)

2) - alkali (eg. sodium hydroxide solution)

35
Q

What are aromatic amines useful for?

A
  • dyes
  • pharmaceuticals
36
Q

What is an amide?

A

Carboxylic acid derivative (group -CONH2)

37
Q

Why do amides behave differently to amines?

A

The carbonyl group pulls electrons away from the NH2 group.

38
Q

What is an N-substituted amide?

A

When one of the hydrogens in an amide is replaced with an alkyl group.

A Level Organic Chemistry (9 decks)

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