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Module 6- Organic Chemistry > 25 Aromatic Chemistry > Flashcards

25 Aromatic Chemistry Flashcards

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1
Q

Benzene is a carcinogen, what does this mean? (1 mark)

A

It causes cancer.

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2
Q

What is the prefix of benzene? (1 mark)

A

phenyl

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3
Q

Describe the Kekulé model of benzene. (2 marks)

A

Six carbon ring with alternate single and double bonds.

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4
Q

Explain how the lack of reactivity of benzene disproves Kekulé’s model of benzene. (3 marks)

A

Benzene should descolourise bromine water if it contains carbon double bonds.
However:
Benzene does not undergo electrophilic addition reactions.
Benzene does not decolourise bromine under normal conditions.

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5
Q

Explain how the lengths of the carbon-carbon bonds in benzene disprove Kekulé’s model of benzene. (2 marks)

A

All the bonds in benzene are the same length, between the lengths of a single and double bond.

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6
Q

How were the carbon-carbon bonds in benzene measured? (1 mark)

A

Using X-ray diffraction

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7
Q

Explain how hydrogenation enthalpies can be used to disprove Kekulé’s model of benzene. (3 marks)

A

The expected enthalpy change of hydrogenation is 3 times that of cyclohexene (as it has 1 double bond and benzene has 3).
In reality, the hydrogenation of benzene is lower than expected.
This means that benzene is more stable than the Kekulé model suggests.

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8
Q

Describe the delocalised model of benzene. (2 marks)

A

Each carbon atom has one electron in a p-orbital.
There is a delocalised pi-electron density above and below the plan of benzene ring.

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9
Q

How are the rings of electron density formed above and below the benzene ring plane? (1 mark)

A

Adjacent p-orbital electrons overlap sideways.

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10
Q

What does it mean if benzene is monosubstituted? (1 mark)

A

Only one hydrogen in benzene has been substituted for a different atom/group.

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11
Q

When is the prefix for benzene used? (1 mark)

A

When benzene is attached to a carbon chain of 7 or more.
When it is attached to an alkyl chain with a functional group.

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12
Q

Name three exceptions to naming aromatic compounds. (3 marks)

A

Benzoic acid
Phenylamine
Benzaldehyde

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13
Q

Are compounds that contain delocalised electrons more or less stable than those that don’t? (1 mark)

A

More stable.

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14
Q

Does benzene undergo electrophilic substitution? (1 mark)

A

Yes

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15
Q

What is the catalyst for the nitration of benzene? (1 mark)

A

Concentrated H2SO4

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16
Q

What reagents are in the nitrating mixture used to nitrate benzene? (2 marks)

A

Concentrated HNO3
Concentrated H2SO4

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17
Q

What temperature should the nitration of benzene take place at? (1 mark)

A

50 degrees

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18
Q

What happens if the temperature goes above 50 degrees when nitrating benzene? (1 mark)

A

Further substitutions take place, to produce dinitrobenzene.

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19
Q

(if have paper)
Draw the mechanism of the nitration of benzene. (5 marks)

A
  1. Equation(s) to show the production of nitrite ion.
  2. Curly arrow from ring to nitrite ion.
  3. Arrow from bond that links hydrogen to ring in intermediate.
  4. The ring doesn’t go past carbons 2 and 6 in intermediate.
  5. Correct products and regeneration of sulfuric acid.
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20
Q

What do halogens need to react with benzene? (1 mark)

A

A catalyst called a halogen carrier.

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21
Q

What are the reagents and conditions for the bromination of benzene? (2 marks)

A

RTP
React with AlBr3 or FeBr3

22
Q

What are the products of the bromination of benzene? (1 mark)

A

Bromobenzene
Hydrogen bromide

23
Q

(if have paper)
Draw the mechanism of the chlorination of benzene. (5 marks)

A
  1. Equation(s) to show the production of chlorine ion (with 1+ charge).
  2. Curly arrow from ring to chlorine ion.
  3. Arrow from bond that links hydrogen to ring in intermediate.
  4. The ring doesn’t go past carbons 2 and 6 in intermediate.
  5. Correct products and regeneration of FeCl3/AlCl3.
24
Q

What is alkylation? (1 mark)

A

The addition of an alkyl group (contains C and H, with single C bonds).

25
Q

What does benzene react with to produce an alkylbenzene? (1 mark)

A

A haloalkane.

26
Q

What is the catalyst used in the alkylation of benzene? (1 mark)

A

AlCl3

27
Q

(if have paper)
Draw the mechanism to produce ethylbenzene. (5 marks)

A
  1. Equation(s) to show the production of electrophile ion (with 1+ charge), from chloroethane and AlCl3.
  2. Curly arrow from ring to electrophile.
  3. Arrow from bond that links hydrogen to ring in intermediate.
  4. The ring doesn’t go past carbons 2 and 6 in intermediate.
  5. Correct products and regeneration of AlCl3.
28
Q

What is acylation? (1 mark)

A

The addition of an acyl group (R-C=O).

29
Q

What does benzene react with to produce an aromatic ketone? (1 mark)

A

Acylchloride

30
Q

What is the catalyst used in the acylation of benzene? (1 mark)

A

AlCl3

31
Q

(if have paper)
Draw the mechanism to produce phenylpropanone. (5 marks)

A
  1. Equation(s) to show the production of electrophile ion (with 1+ charge), from propanoylchloride and AlCl3.
  2. Curly arrow from ring to electrophile.
  3. Arrow from bond that links hydrogen to ring in intermediate.
  4. The ring doesn’t go past carbons 2 and 6 in intermediate.
  5. Correct products and regeneration of AlCl3.
32
Q

Why does benzene need a halogen carrier catalyst to react with bromine, but an alkene doesn’t? (3 marks)

A

Benzene has delocalised electrons spread above and below the plane.
This means the electron density around any 2 carbons in a benzene ring is less than a C=C bond in an alkene.
So when a non-polar molecule, like bromine, approaches benzene there is insufficient pi-electron density to polarise the molecule.

33
Q

What are the reagents and conditions of the alkylation of benzene? (2 marks)

A

Haloalkane
AlCl3
Reflux

34
Q

What are the reagents and conditions of the acylation of benzene? (3 marks)

A

Acylchloride
Anhydrous conditions
AlCl3
Reflux

35
Q

How does an alkene decolourise bromine water?

A

By electrophilic addition.

36
Q

What is a phenol? (1 mark)

A

An organic compound that contains a hydroxyl group bonded to an aromatic ring.

37
Q

Why are phenols less soluble in water than alcohols? (1 mark)

A

Because of the presence of the non-polar benzene ring.

38
Q

What do phenols partially dissociate into in water? (1 mark)

A

A phenoxide ion and a proton.

39
Q

Do phenols react with sodium hydroxide? (1 mark)

A

Yes

40
Q

What is produced when phenol and sodium hydroxide react? (2 marks)

A

Sodium phenoxide
Water

41
Q

Draw sodium phenoxide. (1 mark)

A

Look it up

42
Q

What is produced when phenol and bromine react? (2 marks)

A

2, 4, 6- tribromophenol
3HBr

43
Q

What two products can be produced when phenol reacts with nitric acid? (2 marks)

A

2-nitrophenol
or
4-nitrophenol

44
Q

What are the reagents and conditions for the nitration of phenol? (1 mark)

A

Dilute nitric acid
RTP

45
Q

What are the reagents and conditions for the bromination of phenol? (1 mark)

A

Bromine water
RTP

46
Q

Why is phenol more reactive than benzene? (4 marks)

A

The O in the OH groups contributes another lone pair of electrons
to the pi-system of phenol,
this increases the electron density of the molecule,
making it more susceptible to electrophilic attack.

47
Q

What is observed when phenol reacts with bromine water? (1 mark)

A

A white precipitate is formed.

48
Q

What is an activating group, in aromatic chemistry, and how do they work? (4 marks)

A

Is electron donating,
and makes the aromatic ring more susceptible to electrophilic attack,
by increasing the electron density in the benzene ring
at positions 2, 4, and 6.

49
Q

What is a deactivating group? (5 marks)

A

ls electron withdrawing
and makes the aromatic ring less susceptible to electrophilic attack,
by decreasing the electron density at positions 2, 4, and 6.
This means electrophiles are more likely to bond at carbons 3 and 5.

50
Q

Why are deactivating groups 3-5 directing? (3 marks)

A

They withdraw electron density form the benzene ring,
decreasing electron density at positions 2, 4, and 6,
therefore electrophiles relatively more likely to bond to positions 3 and 5.

51
Q

Why does chlorine react more readily with a C6H5N(CH3)2 than benzene? (3 marks)

A

Lone pair on nitrogen becomes partly dissociated into the pi bond system in benzene ring.
This causes the electron density to increase.
The benzene ring in the molecule has a greater ability to polarise the Cl-Cl bond.

Module 6- Organic Chemistry (5 decks)

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