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Chemistry year 13 a-level rev rev revision > Module 6.1 - Aromatic Compounds, Carbonyls, Acids > Flashcards

Module 6.1 - Aromatic Compounds, Carbonyls, Acids Flashcards

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1
Q

What is Benzene?

A

C6H6 - liquid at room temp - aromatic ring

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2
Q

What is Kekulé’s model?

A

Each carbon has a hydrogen attatched, with 3 stationary pi bonds.

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3
Q

What were the problems with Kekulé’s model?

A
  1. Benzene is resistant to addition reactions
  2. Enthalpy of Hydrogenation of Benzene shows it is much more stable than predicted
  3. All six carbon-carbon bonds are the same length
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4
Q

What is the Delocalized Structure?

A
  • each of the six carbons donates one electron ftom its p-orbital
  • electrons combine to form a plane of delocalized electrons which is present both below and above the plane of the carbon ring.
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5
Q

How does the delocalized structure solve the problems that Kekulé’s model had?

A
  • Due to all electrons being able to move freely, all bond lengths are the same
  • Any sort of addition reaction would disrupt the aromaticity of the electron cloud, hence why benzene resists it
  • The delocalization of the electrons leads to benzene being roughly 152 kJmol-1 more stable than expected.
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6
Q

Instead of addition reactions, what reaction will Benzene undergo?

A

Substitution - preserves the aromaticity of the electron rings.

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7
Q

What is Nitration?

A

An electrophilic substitution reaction where a hydrogen is exchanged for a nitro group (-NO2)
- conc. HNO3 + conc. H2SO4 required.

C6H6 + HNO3 -> C6H5NO2 + H2O

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8
Q

Why is a halogen carrier required for halogenation?

A

The aromatic ring is too stable - the electron cloud alone cannot induce a dipole.

Br2 + FeBr3 -> Br+ + FeBr4-
The Br+ ion can then act as an electrophile, allowing for electrophilic substitution to take place

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9
Q

What are the halogen carriers required for chlorination?

A

AlCl3 or FeCl3

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10
Q

What are the halogen carriers required for bromination?

A

AlBr3 or FeBr3

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11
Q

What is the equation for halogenation ?

A

C6H6 + Br+ -> C6H5Br + H+

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12
Q

What is a Friedel-Crafts reaction?

A

Adding an R (alkyl) group to an aromatic ring at any point

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13
Q

What is the equation to show the preparation of an R group for a Friedel-Crafts reaction?

A

RCl + FeCl3 -> R+ + FeCl4-

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14
Q

What is the equation for acylation with Benzene?

A

C6H6 + RCOCl -> C6H5COR + H+

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15
Q

What is Phenol?

A

an aromatic compound with a hydroxyl group directly attatched to the carbon ring

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16
Q

What sort of substance is phenol?

A

Weak acid - partially dissociates in water

C6H5OH + H2O ⇌ H3O+ + C6H5O-

17
Q

Why is Phenol more reactive than Benzene?

A

Due to the p-orbital electons of the oxygen on the hydroxyl adding more electrons to the rings, making the pi system more nucleophilic - increase in electron density increases susceptibility to electrophilic attack - can now induce a dipole in non polar molecules.

18
Q

What are the products of the reaction of Phenol and excess Bromine?

A

C6H2Br3OH + 3HBr

triple substitution

19
Q

What is the product of the reaction of Phenol with dilute nitric acid?

A

a mixture of 2-nitrophenol and 4-nitrophenol (+H2O)

20
Q

What is the product of the reaction of Phenol with concentrated nitric acid?

A

2,4,6 - trinitrophenol

21
Q

What is the 2,4 directing effect?

A

the effect caused due to phenol pushing additional electrons into the pi system, making substitution reactions occur mainly at the 2 and 4 points in the ring.

22
Q

What is the difference between an Aldehyde and a Ketone?

A
  • An aldehyde has the carbonyl group at the end of the carbon chain
  • A ketone has the carbonyl group not at the end of the carbon chain
23
Q

What happens when you oxidise an aldehyde?

A

It forms a carboxylic acid

24
Q

What happens when you oxidise an ketone?

A

nothing

25
Q

What is the equation for oxidation of an aldehyde?

A

CH3CHO + [O] -> CH3COOH

26
Q

What is Sodium Borohydride (NaBH4) used for?

A

Acts as a source of Hydride ions (H-)

Is made of a Na+ and a BH4- ion

27
Q

What is the reducing agent known as?

A

[H]

28
Q

Give the equation for the reduction of pentan-2-one

A

CH3COC3H7 + 2[H] -> CH3CH(OH)C3H7

Chemistry year 13 a-level rev rev revision (8 decks)

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