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Chemistry > Aromatic Compounds > Flashcards

Aromatic Compounds Flashcards

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1
Q

Describe benzene

A

Six carbon ring

Highly flammable

Component of crude oil and petrol

Carcinogenic

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2
Q

Describe kekules model of benzene

A

Alternating double bonds

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3
Q

Why was kekules model disproved

A

The reactivity, bond length and enthalpy of hydrogenation could not be explained

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4
Q

Describe how the reactivity of benzene is not explained by kekules model

A

Resistance to reaction

Doesn’t undergo electrophillic addition

Doesn’t decolorise bromine water

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5
Q

Describe how the bond lengths in benzene is not explained by kekules model

A

Bond lengths of benzene are between single and double bonds

All Same length

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6
Q

What is used to measure bond lengths

A

X Ray diffraction

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7
Q

Describe how the enthalpy change of hydrogenation of benzene is not explained by kekules model

A

Should be 3x that of cyclo hexene but is not as exothermic

Benzene is more stable

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8
Q

Describe the de localised model of benzene

A

All bonds are same length between double and single bonds

Pi system because of overlap of p orbitals (de localised ring )

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9
Q

What type of reaction does benzene undergo, why

A

Electrophillic substitution

Not addition because no double to break

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10
Q

What conditions are required for nitration

A

50 degrees sulphuric acid catalyst and nitric acid

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11
Q

What conditions are needed for polysubstitution of nitrate

A

Temp of greater than 50

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12
Q

What are the uses of nitro benzene

A

Dyes pharmaceuticals and pesticides

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13
Q

Why are arenes less reactive than alkenes

A

De localised electrons (not localised like in alkenes) means less electron density to un able to polarise

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14
Q

Name the reagents needed for the Halogenation of benzene

A

Halogen carrier

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15
Q

What are the reagents needed for alkylation of benzene

A

Haloalkane

Halogen carrier

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16
Q

What is a Halogen carrier

A

Iron or aluminium chloride or bromide

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17
Q

What is acylation

A

Formation of aromatic ketone

18
Q

What is phenol

A

Benzene with an alcohol group

19
Q

Compare the acidity and solubility of phenol compared to alcohols

A

Phenol is less soluble and more acidic

Benzene is non-polar

20
Q

Is a phenol a weak or strong acid and why

A

Weak as it partially dissociate to produce a phenoxide ion

21
Q

How do you distinguish between an alcohol, phenol and a carboxylic acid

A

Carboxylic acid is the only one to react with sodium carbonate to produce carbon dioxide

Phenol only reacts with sodium hydroxide

Alcohols don’t react with either

22
Q

What salt is produced when phenol reacts with naoh

A

Sodium phenoxide

23
Q

By what mechanism does phenol react with halogens

A

Electrophillic substitution

24
Q

Why is phenol more reactive than benzene

A

OH has a lone pair which is delocalised into the pi system increasing the electro density of it polo rising halogens easier

25
Q

What are the observation conditions and reagents in the bromination of phenol

A

Room temp
No Halogen carrier
White precipitate formed
Orange to colourless

26
Q

What are the observation conditions and reagents in the nitration of phenol

A

Room temp
Dilute naoh
No acid catalyst

27
Q

What two products may be formed in the nitration of phenol

A

2 nitro phenol

4 nitro phenol

And water

28
Q

What is the qualitative test for phenol

A

Neutral iron chloride

Yellow to purple

29
Q

What are the two types of substitutent groups add the benzene

A

Activating and deactivating

30
Q

Describe activating substitutents

A

Electron donating/delocalising
Makes pi system more e dense
Makes benzene more reactive
Milder conditions needed

31
Q

Describe deactivating substitutents

A

Withdraws electrons from pi system

Makes less reactive (need catalyst and higher temp)

32
Q

Give examples of activating groups

A

OH

33
Q

Give examples of deactivating groups

A

NO2

34
Q

What does ortho mean

A

Substituted Next to

35
Q

What does meta mean

A

Substitution one space away

36
Q

What does para mean

A

Substitution opposite to

37
Q

What is a directing effect

A

The effect that a substitutent has on the position of substitution

38
Q

Give examples of 2, 4 directing groups

A

NH2 or NHR

OH

OR

R/C6H5

F, Cl, Br

39
Q

Give examples of 3-directing groups

A

Ketones

COOR (esters)

SO3H

aldehyde

Carboxylic acids

CN

NO2

NR3
amines

40
Q

What is the general rule for knowing whether a group is 2,4 or 3 directing

A

3,5= double or triple bonds

2,4= single bonds only

41
Q

What kind of groups are 2, 4 directing

A

Electron donating

Activating

42
Q

What kind of groups are 3 directing

A

Electron withdrawing

Deactivating

Chemistry (28 decks)

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