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X A2 chemistry > unit 5 section 9 organic compounds > Flashcards

unit 5 section 9 organic compounds Flashcards

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1
Q

what are the two different structures of representing benzene?

A

6 carbons in a loop with every other bond a double one.

A loop of carbons, each making 3 bonds and electrons delocalised around the ring with a circle in the middle.

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2
Q

what is the name of OH bonded to benzene?

A

phenol

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3
Q

what is phenylamine?

A

NH2 bonded to benzene.

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4
Q

what is the name of the model of benzene with 3 double bonds?

A

the kekule model.

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5
Q

what evidence goes against the kekule model?

A

It says that there would be two different bond lengths from double and single bonds, but X-ray diffraction shows they are all the same length and between the two.
Infrared studies show that none of bonds are single or double as none of them absorb at the correct frequencies.
Also enthalpy

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6
Q

what is the structure of the delocalised model for benzene?

A

The p-orbitals of all the carbons overlap to give pi bonds., giving 2 ring shaped cloud of electrons above and below the carbon ring.

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7
Q

What does enthalpy suggest about the structure of benzene?

A

Cyclohexene has one double bond and when hydrogenated enthalpy is -120.
The kekule model has 3 double bonds suggesting it would be -360 for benzene.
It is actually -208 suggesting more energy was used to brake the bonds, subtracting from that given when bonds where made.
Thus the delocalised model is more stable.

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8
Q

How does benzene burn?

A

It has a very sooty flame and it give water and CO2.

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9
Q

why does benzene take part in electrophilic substitution reactions?

A

It is an area of high electron density so it attracts electrophiles. As it is so stable it undergoes substitution which preserve the delocalised ring.

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10
Q

what is the nitronium ion?

A

A positive nitrogen which has 2 double bonds to two oxygen’s.

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11
Q

What is the mechanism for the nitronium ion reacting with benzene?

A

It attacks the stable ring.(arrow from circle goes to ion)
An unstable intermediate forms. The ion and an H are both bonded to a carbon and the circle has a gap in it next to this carbon with +. An arrow from the H bond goes to the + sign and the H+ ion leaves.

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12
Q

What do you have to do to make nitrobenzene?

A

Warm benzene with concentrated nitric and sulphuric acid. The nitrobenzene forms a layer which will float on top. The sulphuric acts as a catalyst and keep the temp below 55 degrees for mononitration.

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13
Q

How is the nitronium ions formed from sulphuric and nitric acid?

A

HNO₃ + H₂SO₄ = H₂NO₃⁺ + HSO₄⁻
H₂NO₃⁺ = NO₂⁺ + H₂O
The H+ from the reaction goes with HSO₄⁻ to give more sulphuric acid to act as a catalyst.

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14
Q

How is benzenesulfonic acid made?

A

warm benzene to 40 degrees with fuming sulphuric acid for half an hour.

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15
Q

What is fuming sulphuric acid?

A

sulphur trioxide (SO3) dissolved in sulphuric acid.

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16
Q

what is the structure if sulphur trioxide?

A

S with 3 triple bonds to 3 oxygens.

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17
Q

How does SO3 react with benzene?

A

A pair of electrons are drawn from the circle to the sigma positive sulphur. An arrow goes from the sulphur to one of the oxygens, giving O:⁻
This O:⁻ will have an arrow going from it to a H attracted to the carbon ring and an arrow will go from the H bond to the gap in the circle with the +
It ends with benzene bonded to S double bonded to 2 oxygens and 1 OH.

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18
Q

Why are halogen carriers needed?

A

An electrophile needs to have a very strong positive charge to react with the stable benzene. The halogen carrier acts as a catalyst to make them more polar.

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19
Q

How does a halogen carrier work?

A

They can accept a lone pair of electrons from the halogen in the electrophile making it more polar.
Sometimes a carbocation can form when the halogen of the electrophile is taken off to give a positive and negative ions

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20
Q

When does an alkylbezene form?

A

React benzene with a halogenoalkane and a halogen carrier(usually aluminium choride)
a friedel crafts alkylation reaction

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21
Q

What is the formula for a chloroalkane reacting with AlCl3?

A

RCl + AlCl3 = R+ + AlCl4-

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22
Q

How would the electrophile R+ react with benzene?

A

An arrow goes from the circle to the R+. This will give the R and H bonded to the same point on the benzene with a gap in the circle with a plus sign.
The AlCl4 will then react with the H. An arrow from a Cl-Al bond will go to the H and this will give HCl and AlCl3 with R attached to the benzene.

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23
Q

What is AlCl3 sensitive to and what does this mean for its reactions?

A

Hydrolysis. All of its reactions are done in dry conditions. When being used benzene and alkanes that are refluxed in dry ether.

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24
Q

Why do acyl chlorides react readily with benzene?

What do they form and how is it done?

A

They are polar molecules so they can easily form carbocations. They need a halogen carrier and react by electrophilic substitution to form a phenylketones.

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25
Q

What is the equation for an acid chloride to form a electrophile?

A

RCOCl + AlCl3 =RCO+ and AlCl4-

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26
Q

what is the structure of an acid chloride?

A

R bonded to C. This is double bonded to O and has a single bond to Cl.

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27
Q

How does the RCO+ carbocation react with benzene?

A

It attacks the pi cloud. Arrow from circle to C+
H and C are bonded to same point of the carbon ring with a gap in the circle with a +. Arrow goes from C-H to the circle and arrow from a Al-Cl bond of AlCl4 goes to the H.
This will give HCl and AlCl3.

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28
Q

What is a phenylketone ?

A

A benzene ring bonded to carbon double bonded to oxygen and R.
They are less reactive than benzene.

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29
Q

what are friedel crafts acylation reactions ?

A

An acid chloride will use a halogen carrier to react with benzene

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30
Q

What is the condition needed for a friedel crafts acylation reaction?

A

The mixture is heated under reflux with a dry either.

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31
Q

Why won’t benzene decoluorise bromine water like cyclohexene?

A

It takes more energy to break the delocalised electron ring.

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32
Q

Why does benzene need strong electrophiles to react with them?

A

It has the very stable delocalised electron ring. This means it will need an ion with a +1 charge and not just something with a sigma positive charge.

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33
Q

How do you get bromine to react with benzene?

A

Use FeBr3 to act as halgen carrier to give Br+

It reacts in the same way as the other electrophilic substitution reactions.

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34
Q

How can benzene take part in an addition reaction?

A

It will react with hydrogen with finely divided nickel catalyst at 150 degrees and 10 atm to give cyclohexane.

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35
Q

What might be used instead of benzene when doing some of the electrophilic substation reactions of benzene

A

You might use methyl or methyloxybenzene.
They are more reactive and the rate of reaction is faster than that of benzene.
They are also a lot less toxic.

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36
Q

what is the structure of methyl or methlyloxybenzene?

A

A benzene ring with CH3 added or -O-CH3

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37
Q

Why are methyl or methlyloxybenzene more reactive than benzene?

A

The additional groups donate electrons to the pi cloud meaning that there is a larger electron density meaning there are more willing to donate electrons.

38
Q

What is phenol?

A

A benzene ring with OH bonded to one of carbons.

39
Q

Does phenol react with bromine water?

A

Yes. It gives 2,4,6-tribomophenol with is a white insoluble precipitate with an antiseptic smell.

40
Q

Why does phenol react with bromine water?

A

One of the electron pairs in a p orbital of the oxygen atom overlaps with the delocalised ring of the benzene ring. This will increase the electron density at 2,4 and 6 positions on the ring. It is at these points where bromine will be added.

41
Q

How is phenol nitrated?

A

Add dilute nitric acid.

42
Q

What is required to nitrate benzene?

A

Conc nitric acid and conc sulphuric acid catalyst.

43
Q

What does the nitration of phenol give?

A

Water and two isomers of nitophenol. 2 and 4 nitrophenol.

44
Q

what are the two types of organic chemicals.

A

aliphatic : straight or branched chain organic substances aromatic or arene: includes one or more ring of six carbon atoms with delocalised bonding.

45
Q

what is benzaldehyde?

A

Benzene with COH

46
Q

What is benzenecarboxylic acid

A

benzene and CO2H

47
Q

how might you produce iron bromide in situ?

A

Add iron to the bromine.

48
Q

What is the cause of some of the physical properties of phenol?

A

The delocalised electron ring will extend to the O and the C-O bond will be stronger while the O-H bond is made weaker.
It will act more like a weak acid than an alcohol and it can’t be oxidised.

49
Q

what is the systematic name of the hypothetical kekule model?

A

1,3,5 cyclohexatriene

50
Q

How does sulphur trioxide form?

A

H2SO4 = SO3 +H2O

51
Q

what are the conditions needed to add a nitro group to phenoll?

A

Just use dilute nitric.

No need for heat or sulphuric

52
Q

At a basic level, how is an amine formed?

A

One of the hydrogens of ammonia is replaced with an organic group.

53
Q

What do amines smell like?

A

Smaller ones like ammonia.

A fish smell gets stronger as they get larger

54
Q

Do amines dissolve in water?

A

They form hydrogen bonds with water and dissolve
the larger it is the greater van der waals between them so less soluble.
They form alkaline, as they take a hydrogen ion from the water and give OH-

55
Q

Do amines act as bases?

A

The lone pair of electrons on the nitrogen atom can form a dative covalent bond for N+H3
They make ammonium salts with acids such as CH₃NH₃⁺Cl⁻

56
Q

How would HCl react with a amine?

A

The nitrogen would bond to the hydrogen and become N⁺ and bond to Cl⁻

57
Q

what does Cu²⁺ do in copper sulphate?

A

form [Cu(H₂O) ₆]²⁺ with the water.

58
Q

What happens when a small amount of methylamine is added to copper sulphate?

A

The amine acts as a proton accepter and takes 2 H+ from the
[Cu(H₂O) ₆]²⁺ complex. The insoluble [Cu(H₂O)₄(OH)₂] will form and precipitate out to give a blue colour.

59
Q

What happens when more methylamine is added to copper sulphate?

A

the copper hydroxide precipitate dissolves to give a deep blue solution.
Methylamine molecules donate their lone pairs to give dative covalent bonds with the Cu²⁺ to give soluble
[Cu(CH₃NH₂)₄(H₂O)₂]²⁺ ions.
This set of reactions is the same for other amine molecules though the final product may be different as they can’t all fit around the copper

60
Q

What happens when amines react with acid chlorides?

A

A H atom of the amine is replaced with the acyl group (ROCl) to produce an N-substitiuted amide and HCl which will later to go on to react with the amine and give a salt.

61
Q

what is observered when an acid chloride is reacted with an amine?

A

A violent reaction happens, which gives solid, white mixture of the products.

62
Q

How does an amine react with a halgenolkane?

A

The lone pair of electrons on the nitrogen will attack the sigma positive carbon to give a salt of the two. The negative halogen will then take a hydrogen away to give HX and a secondary amine

63
Q

How can paracetamol get formed?

A

Ethanoyl chloride reacts with p-aminophenol to give HCl and paracetamol

64
Q

What does the p in p-aminopheol mean?

A

Short for para.

the OH and NH2 groups are on opposite sides of the benzene ring.

65
Q

What is an amide?

A

A derivative of carboxylic acid. The OH of acid group is replaced with NH2 and all amines have the -CONH2 group.

66
Q

What is a N-substituted amide?

A

An amide group that with one of H bonded to the N replaced with an alkyl group.

67
Q

What is acylation?

A

When an acyl group replaces a H atom.

68
Q

What happens when ammonia is reacted with an acid chloride?

A

An amide and HCl is formed. The HCl can then form an ammonium salt.

69
Q

How are aromatic amines formed?

A

A nitro compound like nitro benzene is reduced by heating with tin and conc HCl under reflux to give an ammonium salt.
Then sodium hydroxide is added to remove H+ ions from the salt giving an aromatic amine.

70
Q

What is the azo group?

A

-N=N-

71
Q

How are azo dyes made?

A

phenols and aromatic amines are reacted.

Normally two aromatic groups are joined as this gives a very stable molecule.

72
Q

what is an amino acid?

A

it has a basic ammino group (NH2) and an acidic carboxylic group (COOH).
There are amphoteric meaning that they have both acidic and basic properties.

73
Q

What is an alpha amino acid?

A

The amino and carboxyl group are attached to the same carbon atom.

74
Q

What is the simplest alpha amino acid?

A

Glycine. The simplest possible alpha amino acid.

H2N then CH2 then COOH.

75
Q

what is alanine?

A

Like gycine but one the H of the middle CH2 is replaced with a CH3

76
Q

What is the structure of phenylalanine?

A

Benzene bonded to CH2, which is bonded to the central C of glycine.

77
Q

What is cysteine?

A

Like phenylalanine but SH instead of benzene.

78
Q

What are zwitterions?

A

A dipolar ion. It has a positive and negative charge on different parts of the ion. It only happens near the isoelectric point. It is the pH where the average overall charge on the acid is zero.

79
Q

What happens to an amino acid at a low pH?

A

NH2 Likely to be propanated to give N+H3

80
Q

What happens to an amino acid at a high pH?

A

The -COOH group is more likely to lose its proton to give COO-

81
Q

How would you carry out paper chromatography to identify an unknown amino acid?

A

Draw near the bottom of filter paper and point a spot of acid on it. Put the bottom of the paper in solvent and as this rises it will take the acid with it and give another spot higher up.
To see these spots, spray with ninhydrin solution the Rf of the acid is the distance travelled by the spot divided by the solvent.

82
Q

what is the structure of ninhydrin?

A

Benzene attached to pentagon of carbon. Two OH groups bonded to the single carbon on the pentagon opposite the hexagon with =O on each carbon on either side of this carbon.

83
Q

How do you see a solution of colourless amino acid?

A

Add ninhydrin
It reacts with the amino acid to give ammonia,aldehydes,,carbon dioxide and hydrindantin.
Hydrindantin reacts with ammonia and ninhydrin to give the purple pigment of Ruhemass’s purple.

84
Q

what do diazonium compounds contain?

A

-N⁺≡N. Diazonium salts aren’t stable so they have to be used straight after being formed.

85
Q

what is the basic principle behind making an azo dye?

A

Make a diazonium salt, which is then coupled to an aromatic compound that is susceptible to electrophilic attack, like a phenol.

86
Q

How might you make a diazonium salt to make an azo dye?

A

First make some nitrous acid. Has to be made in situ because it is unstable.
NaNO2 +HCl=HNO2 + NaCl
The acid reacts with HCl and phenylamine to give benzenediazonium chloride and water. Temp must be around 5 degrees to prevent phenol from forming.

87
Q

What is the structure of benzenediazonium chloride

A

A benzene ring bonded to -N⁺≡N Cl⁻

88
Q

How do you use benzenediazonium chloride to make an azo dye?

A

Dissolve phenol in sodium hydroxide to give sodium phenoxide solution.
Stand in ice and add chilled benzenediazonium chloride
The azo dye precipitate out.
The OH of the phenol increases the electron density of the benzene ring and allows the diazonium ion (weak eletrophile) to attack.

89
Q

what is the equation of benzenediazonium chloride reacting with phenol to give azo dye?

A

Phenol +NaOH + benzenediazonium chloride = H2O + NaCl + a benzene ring bonded to N=N bonded to phenol.

90
Q

Why are azo dyes stable?

A

the -N=N- group becomes part of the delocalised electron system.

X A2 chemistry (12 decks)

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