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Chemistry A2 Rafa > 6.1 Aromatic compounds, carbonyls and acids > Flashcards

6.1 Aromatic compounds, carbonyls and acids Flashcards

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1
Q

Define benzene

A

A naturally occurring aromatic compound, which is a very stable planar ring structure with delocalised electrons.

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2
Q

Define model

A

A simplified version that allows us to make predictions and understand observations more easily.

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3
Q

Define substitution reaction

A

Where a group or atom is exchanged for another group or atom in a chemical reaction

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4
Q

Define benzene derivative

A

Benzene ring that has undergone a substitution reaction

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5
Q

Define electrophilic substitution

A

a substitution reaction where an electrophile is attracted to an electron-rich atom or part of a molecule and a new covalent bond is formed by the electrophile accepting an electron pair.

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6
Q

Define reaction mechanism

A

A model with steps to explain and predict a chemical reaction.

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7
Q

What is a Friedel-Crafts reaction?

A

A substitution reaction where hydrogen is exchanged for an alkyl or acyl, chain.

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8
Q

What are phenols?

A

A class or aromatic compounds where a hydroxyl group is directly attached to the aromatic ring.

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9
Q

What is the directing effect?

A

How a functional group attached directly to an aromatic ring affects which carbon atoms are more likely to undergo substitution.

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10
Q

Define nucelophile.

A

A species attracted to an electron-deficient part of a molecule, where it donates a pair of electrons to make a new covalent bond.

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11
Q

What did Kekule discover?

A

When one group was attached to the benzene, only one isomer was ever made
When two groups were added there were always three structural isomers.

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12
Q

Problems with Kekule model

A
  • Benzene is resistant to addition reactions
  • Enthalpy of hydrogenation shows that benzene is much more stable then predicted
  • All six carbon bonds were the same length
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13
Q

How did Kekule explain the resistance to reaction?

A

By saying the double and single bonds changed position in a very fast equilibrium.

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14
Q

Explain the delocalised structure of benzene

A

Each of the six carbon atoms donates one electron from its p-orbital.
Form ring above and below.

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15
Q

Why is benzene very stable?

A

A lot of energy is needed to disrupt the delocalisation.

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16
Q

What do hydrogen carriers include?

A

Iron
Iron halides
Aluminium halides

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17
Q

Nitration of benzene describe process

A

Nitric and sulphuric acid mixed in a flask and held in an ice bath
Benzene added under reflux
Condenser
Keep at 50 degrees

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18
Q

Why is the sulphuric acid needed in nitration of benzene?

A

To generate the NO2+ electrophile from the nitric acid

Catalyst as it is regenerated

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19
Q

What is a base?

A

A chemical that will react with an acid

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20
Q

What do you need when you add alkyl groups to benzene?

A

Strong Lewis acid

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21
Q

What is a Lewis acid?

A

Accepts a pair of electrons

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22
Q

Functional group of acyl chloride

A

RCOCl

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23
Q

Use of acyl chloride

A

Used in friedel crafts reaction as the halogen carrier

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24
Q

Conditions for acylation of benzene

A 
60 degrees
30 mins
Reflux 
AlCl3 catalyst
Anhydrous conditions
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25
Q

Testing for carbonyl functional group

A

Brady’s reagent
Orange
Mix of methanol, sulfur if acid and a solution of 2,4-dinitrophenylhydrazone

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26
Q

What does Brady’s reagent identify?

A

Ketone or aldehyde but not carboxylic acid or ester

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27
Q

What do you need when you add alkyl groups to benzene?

A

Strong Lewis acid

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28
Q

What is a Lewis acid?

A

Accepts a pair of electrons

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29
Q

Use of acyl chloride

A

Used in friedel crafts reaction as the halogen carrier

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30
Q

What do you use to attach carbonyl groups to aromatic compounds?

A

Acyl chlorides

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31
Q

Why can we only get single substitution when we add carbonyl groups on benzene?

A

The carbonyl group removes electron density from the ring

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32
Q

Why is phenol a weak acid?

A

Because it partially dissociates in water and releases H+

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33
Q

why doesn’t phenol react with weak bases?

A

Because it is a weak acid

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34
Q

Why is phenol more reactive then benzene

A

Higher electron density, non bonding electrons join delocalised system

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35
Q

Things that smell like antiseptic

A

tri bromo and chloro phenol

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36
Q

when is the directing effect more noticable?

A

when we have a NH2 substituted instead of phenol

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37
Q

When do we get a 3 directing effect?

A

with NO2 group attached

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38
Q

Why is there a colour change from orange to green during the oxidation of aldehydes?

A

the oxidation state of the chromium changes

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39
Q

source of H- ions

A

sodium tetrahydrideborate (III), NaBH4

40
Q

formula of cyanide ions

A

CN-

41
Q

Source of cyanide ions

A

HCN and NaCN

42
Q

Why do we acidify the solution before adding CN- to increase chain length?

A

increases the polarity go C=O group

43
Q

What is Brady’s reagent made from?

A

methanol, sulphuric acid and a solution of 2,4 dinitrophenylhydrazine (2,4 - DNP)

44
Q

What does bradys tell us?

A

if there is an aldehyde or ketone present

45
Q

what happens when bradys is added to aldehyde or ketone

A

orange yellow precipitate

46
Q

Why do we measure the boiling points of the precipitates?

A

bigger difference than the substances themselves

47
Q

how do we make Tollen’s reagents?

A

Add sodium hydroxide to silver nitrate solution until a brown precipitate is formed
add dilute ammonia drop by drop until it redissolves

48
Q

What is Tollen’s reagent

A

A weak oxidising agent

49
Q

Why is a silver mirror formed?

A

Silver is oxidised, the Ag+ ions turn into solid silver

50
Q

How do we make esters using carboxylic acids?

A 
Alcohol and carboxylic acid
sulphuric acid and gentle heating
if they are large esters we need to heat under reflux
reversible
not suitable for phenol + derivatives
51
Q

What are the two main ways of making esters?

A

Using carboxylic acids

Using acid anhyrides

52
Q

How do we make esters from acid anhydrides?

A 
acid anhydrides react with alcohols
non reversible reactions
react with phenol + derivatives
higher yield
produces ester and carboxylic acid
53
Q

How can we reverse esterification?

A

Using hydrolysis

54
Q

What happens if we refiux an ester with a hot aqueous acid (acid hydrolysis)

A

reversible decomposition
acid catalyst
alcohol and carboxylic acid

55
Q

Describe alkaline hydrolysis

A

Irreversible decomposition

forms a carboxylate salt and alcohol

56
Q

Whats alkaline hydrolysis used for ?

A

saponification

57
Q

What are acyl chlorides?

A

Derivative of carboxylic acids where the -OH group is replaced by a -Cl group

58
Q

Properties of short chained acyl chlorides?

A

fuming colourless liquids

59
Q

How do we make acyl chlorides?

A

carboxylic acid and SOCl where Cl replaces the OH group

60
Q

Why is it better to use acyl chlorides to make esters?

A

Higher yield

61
Q

Bad thing about using acyl chlorides to form esters

A

HCl fumes

62
Q

How do we get ester involved with aromatic rings?

A

Phenol and carboxylic acid won’t react
using with acyl chlorides
violent reactions that produce corrosive fumes

63
Q

Describe the reaction to form carboxylic acid from acyl chloride

A

Add water
very exothermic
misty HCl fumes

64
Q

Describe forming primary amides using acyl chlorides

A

React with conc ammonia

an ammonium salt is also made

65
Q

Forming secondary amides using acyl chlorides

A

React with primary amines

called N substituted amides (secondary amide another name for)

66
Q

What happens when acyl chlorides react with secondary amines?

A

N,N amides which have two alkyl groups on the nitrogen

67
Q

How do you make Tollen’s reagent?

A

1) Add sodium hydroxide to silver nitrate solution until a brown precipitate forms
2) Add dilute ammonia drop by drop until the precipitate re-dissolves

68
Q

Why does Tollen’s reagent work?

A

its a weak oxidising agent and will oxidise aldehydes but not ketones as they cannot be further oxidised
When oxidising, the Ag+ ions are reduced to solid silver

69
Q

Why are carboxylic acids more soluble than their similar alcohols?

A

Because they can form 2 hydrogen bonds per molecule

70
Q

Properties of short chained acyl chlorides

A

fuming colourless liquids which are very reactive and Cl is replaced by other groups

71
Q

CH3COOH + SOCl2 = ?

A

CH3COCl + SO2 + HCl

and then distil

72
Q

Why are triglycerides soluble in non-polar solvents and not in water?

A

-There is van der Waals between triglycerides.
- There is van der Waals between triglycerides and (non-polar) solvent.
- Triglycerides cannot hydrogen bond (to water)(enough).
-Because there are not enough suitable sites/oxygen atoms
-Or long hydrocarbon chains do not hydrogen
bond/would interfere with hydrogen bonding in water

73
Q

Conditions for alkylation of benzene

A

CH3Cl

AlCl3

74
Q

Conditions for Friedel Crafts acylation of benzene

A
  • reflux
  • 60 degrees
  • 30 mins
  • anhydrous conditions
  • single substitution only
  • CH3COCl
  • AlCl3
75
Q

Conditions for nitration of benzene

A
  • conc nitric and sulphuric mixed in ice bath
  • benzene added
  • reflux condenser set up at 50 degrees
76
Q

Why is the mixture kept at 50 degrees for nitration of benzene?

A

to prevent further substitutions

77
Q

Equation for adding sulphuric acid and nitric acid together in an ice bath

A

H2SO4 + HNO3 = NO2+ + HSO4- + H2O

78
Q

What conditions are needed for the halogenation of benzene?

A
  • X2

- AlX3 or Fe or FeX3

79
Q

How does iron act as a halogen carrier?

A

Forms a iron halide in situ

80
Q

Conditions for the reduction of nitrobenzene

A
  • Reflux at 100 degrees with Sn/conc. HCl

- After refluxing for 20 mins, add NaOH to remove excess acid

81
Q

Why is the 3 directing effect seen on -NO2 groups are attached to the aromatic ring?

A

the nitro groups withdraw electrons from the pi-system

82
Q

Which groups do 2- and 4- directing effect?

A

phenol

NH2

83
Q

Which groups do 3 directing effect?

A

NO2

84
Q

Conditions for adding a nitro group to phenol?

A

dilute HNO3 for single substitution

conc. HNO3 for triple substitution

85
Q

What happens when you add NaOH to phenol?

A

Na+O- salt forms

86
Q

Why are all of the bonds in benzene the same length?

A

the pi bonds are delocalised

87
Q

Acidic hydrolysis of esters

A

alcohol + COOH

reversible

88
Q

Alkaline hydrolysis of esters

A

alcohol and carboxylate salt

not reversible

89
Q

What do you observe when you make a primary amide from an acyl chloride?

A

white smoke

some products remain in colourless solution

90
Q

What do you observe when you make a secondary amide from an acyl chloride?

A

white solid

91
Q

What did they expect the enthalpy of hydrogenation of benzene to be and what was it actually?

A 
expected = -360kJmol-1
actual = -208kJmol-1
92
Q

When is nucleophilic addition?

A

C=O

93
Q

When is electrophilic substitution?

A

Benzene and phenol

94
Q

Why does CH3COCl produce acidic solutions?

A

in water it produces a carboxylic acid and HCl

the carboxylic acid dissociates

95
Q

How to test for phenol?

A
  • add NaOH to form colourless solution

- doesnt effervesce when sodium carbonate or hydrogencarbonate ions are added

Chemistry A2 Rafa (8 decks)

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