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Chemistry > Aromatic Compound's > Flashcards

Aromatic Compound's Flashcards

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1
Q

What is the molecular formula of benzene?

A

C6H6

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2
Q

What is the empirical formula of benzene?

A

CH

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3
Q

What term is given to any molecule that does not contain a benzene ring?

A

Aliphatic

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4
Q

What do aromatic compounds contain?

A

A benzene ring

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5
Q

How many delocalised electrons does benzene contain?

A

6

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6
Q

What are some problems with the Kekules structure?

A

Enthalpies of hydrogenation
Reactivity
C-C bond lengths

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7
Q

Benzene does not undergo electrophilic addition reactions with halogens at room temperature like alkenes so what does it undergo?

A

Benzene will only react with halogens if a catalyst is present. It then undergoes an electrophilic substitution reaction with halogens.

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8
Q

Describe bonding in benzene

A

Each carbon has 4 outer electrons; one is used to bond to a hydrogen; 2 are used to bond to adjacent carbons; the remaining electron from each carbon form a cloud of delocalised electrons above and below the plane of the ring.

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9
Q

Delocalisation gives rise to extra stability called what?

A

Delocalisation energy

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10
Q

If alkyl groups with less than 7 carbons, nitro groups and halogens are attached directly to a benzene ring, they are what?

A

Prefixes to benzene
- put in alphabetical order
- use di, tri and number

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11
Q

If a benzene ring is attached to an alkyl group with a functional group or an alkyl group with 7 or more carbon atoms what prefix is used instead of benzene?

A

Phenyl

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12
Q

What is the prefix/name when there’s a OH attached directly to ring?

A

Phenol

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13
Q

What is the prefix/name when there’s a NH2 attached directly to ring?

A

Phenylamine

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14
Q

What is the prefix/name when there’s a COOH attached directly to ring?

A

Benzoic acid

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15
Q

What is the prefix/name when there’s a CHO attached directly to ring?

A

Benzaldehyde

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16
Q

When are prefixes for NH2 (amino) and OH (hydroxyl) used?

A

When COOH or CHO take priority, or there is more than one amino or hydroxyl group

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17
Q

What are the reactions and conditions for a chlorination reaction?

A

Cl2 with AlCl3 catalyst

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18
Q

What are the reactions and conditions for a bromination reaction?

A

Br2 with AlBr3 catalyst

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19
Q

What are the reactions and conditions for a nitration reaction?

A

Concentrated nitric acid, concentrated sulfuric acid, heat under reflux at 50 degrees for mononitration.

20
Q

What are the reactions and conditions for an alkylation reaction?

A

Alkyl chloride(haloalkane) with AlCl3 catalyst

21
Q

What are the reactions and conditions for an acylation reaction?

A

Acyl chloride with AlCl3 catalyst

22
Q

What does the donation of a proton from the OH group enable?

A

Phenol and carboxylic acids

23
Q

Why do aromatic compounds do electrophilic substitution not addition?

A

Substituting ensures stable pi ring is re-formed

24
Q

Describe the Kekule model of benzene

A

Alternating single and double C-C bonds

25
Q

How does a pi bond form?

A

Sideways overlap of adjacent p orbitals above and below the bonding atoms

26
Q

What is the electrophile in the bromination of benzene?

A

Br+, bromonium ion

27
Q

What type of mechanism do alkenes tend to react in?

A

Electrophilic addition

28
Q

What type of acid is phenol and what does it react with?

A

A weak acid
Reactive metals - Na and bases - NaOH

29
Q

What type of acid is a carboxylic acid and what does it react with?

A

Weak acid
Reactive metals, bases and metal carbonates

30
Q

How does phenol react as a weak acid?

A

The OH group on phenol donates a proton to water when in aqueous solution. This occurs due to delocalisation of the negative charge of the O- around the delocalised pi bond system of the benzene ring. This makes the phenoxy ion more stable.

31
Q

What simple chemical test could you do to distinguish between phenol and a carboxylic acid?

A

Metal carbonate test as phenol will not react with carbonates as it is a very weak acid and carboxylic acids do react with carbonates - effervescence will be observed.

32
Q

Whats the difference between an acid and a base?

A

An acid is a proton donor and a base is a proton acceptor.

33
Q

What is amine?

A

A weak base due to the lone pair on the nitrogen atom.

34
Q

How does increasing the electron density affect the amine as a base?

A

The greater the electron density on the N, the easier it can pick up protons and the amine is a stronger base. This is affected by the groups attached to the nitrogen

35
Q

Describe the reaction of phenylamine as a very weak base.

A

The lone pair on the N is delocalised into the pi bond system, the electron density on N is lowered, the lone pair is less effective at accepting a proton

36
Q

Describe the reaction of methylamine as a weak base.

A

Alkyl groups donate electrons to N, electron density on N is increased and the lone pair is more effective at accepting a proton

37
Q

When amines dissolve in water what do they produce?

A

Weak alkaline solutions

38
Q

When amines react with acids what do they produce?

A

Salts

39
Q

To reform the amine from its salt what do you add?

A

Aqueous sodium hydroxide as NaOH is a stronger base than the amine and accepts a proton from the salt.

40
Q

Does phenol undergo electrophilic substitution much more easily than benzene?

A

Yes

41
Q

Why does phenol undergo electrophilic substitution much more easily than benzene?

A
  • phenol has two lone pairs on the oxygen of the phenol group
  • one of these pairs of electrons is delocalised around the ring
  • this increases the electron density in the pi bond system
  • the electrophile is attracted more easily to the pi bond system
  • a non-polar electrophile can be polarised without the need for a halogen carrier
42
Q

What happens when bromine water is added to a solution of phenol in water?

A

The bromine water is decolourised and a white precipitate forms which smells of antiseptic.

43
Q

Compare the addition of bromine water to phenol and an alkene?

A

Bromine water is normally used as a test for a c=c double bond in an alkene. The important difference with phenol is the formation of a white precipitate as well as the bromine water being delocalised.

44
Q

What happens when you react phenol with dilute nitric acid?

A

Phenol reacts with dilute nitric acid at room temperature to give a mixture of 2-nitrophenol an 4-nitrophenol. This is a mono-nitration.

45
Q

What are the conditions needed to get from nitrobenzene to amino-benzene?

A

Sn (Tin) Conc HCl
Heat under reflux

46
Q

What are the conditions needed to get from nitrobenzene to amino-benzene?

A

Sn (Tin) Conc HCl
Heat under reflux

Chemistry (10 decks)

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