Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A-Level Chemistry > Aromatic Chemistry > Flashcards

Aromatic Chemistry Flashcards

You may prefer our related Brainscape-certified flashcards:
Periodic Table flashcards Chemistry 101 flashcards AP® Chemistry flashcards Organic Chemistry 101 flashcards
1
Q

What are aromatic hydrcarbons?

A

Where some or all of the carbons are found in a benze ring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the benzene ring classed as if there is an alkyl, halogen or nitro group attached?

A

Classed as the parent group so benzene = prefix

eg. Chlororbenzene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What groups have the top priority?

A

Alcohols and amines

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is benzene’s prefix when an alcohol or amine is present?

A

Phenyl

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a benzene ring with an OH group present called?

A

Phenol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Where must the line go when attaching a group?

A

Straight to first element

eg. CH3 —-> C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What was Kekules propsed structure?

A

Planar
Cyclic with alternating double and single bonds
120 degrees bond angles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How was it proved there was no double bonds in the structure? PROBLEM 1

A

Chemist tried reacgting C6H6 with Br2, HBr and H2SO4 but didn’t work
Told us no double bonds as molecule cound not undergo electrophilic addition reactions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What was problem 2?

A

Expected to be irregular hexagon
But used x-ray diffraction to measure bond length
Showed regular shape = c-c bonds same length
+ each bond is an intermediate between a single and a double

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What was problem 3?

A

Cyclohexene’s enthalpy change = -120kjmol-1
Kekules model expected benzene to have -360kjmol-1
But in reality had -208kjmol-1
So showed bonds more stable than alkenes as less exothermic than expected

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Delocalised model of benzene

LEARN IT

A

Each carbon has 3 sigma bonds = leaves a spare electron in 2p orbital
2p orbitals overlap above + below ring
Form pi bond
Electrons in pi bond = delocalised

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is the general equation for halogenation?

A

Benzene + Br2 —-> bromobenzene + HBr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What catalyst is used in halogenation make the halogen carrier?

A

AlBr3

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What must the halogen carrier catalyst contain?

A

The same halogen as the halogen carrier

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the equation for creating the electrophile (step 1) in halognation?

A

Br2 + AlBr3 —-> AlBr4- + HBr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What is the equation for regenerating the catalyst (step 3) in halogenation?

A

AlBr4- + H+ —-> AlBr3 + HBr

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What are the products of the mechanisms for halogenation?

A

Bromobenzene + H+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the general equation for nitration?

A

Benzene + Nitric acid —-> Nitrobenzene + H2O

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What is the equation for the first step of nitration?

A

Nitric acid + sulphuric acid —-> NO2 + + HSO4 -

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What are the products of the mechanism for nitration?

A

Nitrobenzene + H+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is the equation for step 3 of nitration?

A

HSO4- + H+ —-> H2SO4

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What are the conditions needed for nitration?

A

H2SO4 catalyst

50 degrees

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is the order you draw out electrophilic substitution for aromatic chemistry?

A

General equation
Creating the electrophile
Mechanism
Regenerating the catalyst

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What type of reaction is alkylation ans acylation?

A

Friedel Crafts reaction

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is different about alkylation?

A

The alkyl group needs to be attached to a halogen

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the general equation for alkylation?

A

Benzene + Ch3Cl —-> methylbenzene + HCl

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is step 1 of alkylation?

A

CH3Cl + AlCl3 —-> CH3+ + AlCl4-

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is the products of alkylation mechanism?

A

Methylbenzene + H+

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is the third step of alkylation?

A

AlCl4- + H+ —-> AlCl3 + HCl

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is the catalyst of alkylation?

A

AlCl3

But must have the same halogen on as the alkyl group

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

What is the general equation for acylation?

A

Benzene + CH3COCl —-> phenylethanone + HCl

32
Q

What is the equation for step 1 of alcylation?

A

CH3COCl +AlCl3 —-> AlCl4- + CH3CO+

33
Q

What are the products formed in the mechanism for acylation?

A

Pheylethanone (ketone) + H+

34
Q

What is step 3 of acylation?

A

AlCl4- + H+ —-> AlCl3 + HCl

35
Q

What must an electrophile have in electrophilic substitution?

A

A strong positive charge so tha it can attack the benezene ring
Most compounds not polar enough

36
Q

What does a halogen carrier do in electrophilic substitution?

A

Accepts a lone pair of electrons from the halogen carrier

As the lone pair is pulled away polaristaion increases, forming a strong electrophile

37
Q

What is a phenol?

A

Type of organic chemical containing a hydroxyl fuctional group bonded directly to an aromatic ring

38
Q

What type of acid is phenol?

A

Weak acid

39
Q

Is phenol more soluble in water then benzene?

A

YES

40
Q

Is phenol more soluble in water than alcohols?

A

NO

41
Q

Why is phenol less soluble in water than alcohols?

A

Due to non-polar benzene ring on phenol

42
Q

What happens when phenol is dissolved in water?

A

It partially dissociates to form a phenoxide ion and a proton

43
Q

What state is phenol at R.T?

A

Solid

44
Q

What doesn’t ethanol react with?

A

Strong bases (NaOH) or weak bases (Na2CO3)

45
Q

What is the difference between ethanol and phenols and carboxylic acids?

A

Phenols + carboxylic acids will react with solutions of strong bases

46
Q

What is the difference between carboxylic acids and pehnols?

A

Carboxylic acids are the only ones strong enough to react with a weak base

47
Q

What would you observe if a carboxylic acid reacted with a weak base like Na2CO3?

A

Gas/bubbles

48
Q

What is the reaction of phenol with an alkali?

A

Phenol + NaOH —-> sodium phenoxide + H2O

49
Q

What is the reaction of phenol with a metal?

A

Phenol + Na —-> sodium phenoxide + H2

50
Q

In bromination of phenols what does phenol react with?

A

Aqueous solution of bromine (bromine water)

51
Q

At what conditons an bromination of phenols be carried out at?

A

R.T

52
Q

How do you know when bromination of phenols are complete?

A

Br2 water decolourises

OR white precipitate forms

53
Q

What is the reaction of bromination of phenol?

A

Phenol + 3Br2 —-> 2,4,6 tribromophenol + 3HBr

54
Q

What the products of bromination of phenol in the mechanism?

A

Bromophenol + H+

55
Q

Why does phenol react more readily with bromie than benzene?

A

One of the lone pairs on the p-orbital of O atom in OH is partially delocalised into the ring
Increases elcetro density
Electrophile becomes polarised

56
Q

What is different about bromination phenols?

A

Doesn’t require a halogen carrier

57
Q

What does phenols react with in nitration?

A

Nitric acid

58
Q

What is different about nitration of phenols?

A

Doesn’t require a halogen carrier

Can produce different products depending where the NO2 group joins

59
Q

What is the equation for nitration of phenols?

A

Phenol + nitric acid —-> nitrophenol + H2O

60
Q

Why can the nitration of phenols produce either product?

A

Because the -OH group has a 2,4 directing effect

61
Q

What are the products of the mechanism of nitration of phenols?

A

Nitrophenol + H+

62
Q

What is it called when aromatic compounds undergo second substitution?

A

Di-substitution

63
Q

What is the directing effect?

A

The presence of substituted groups on a benzene ring will have an effect on the substitution of further groups

64
Q

How can substituted groups be classified?

A

By the effect they have on electron density of the ring

65
Q

What does electron donating do?

A

Increase electron density

66
Q

What does withdrawing electrons do?

A

Decrease electron density

67
Q

What do side chains that increase electron density do?

A

Allow electrophiles to react faster than with benzene, so are “activating groups”

68
Q

Why are -OH and -NH2 groups activating groups?

A

O + N lone pair orbitals overlap with delocalised ring
So increase electron density at positions 2,4 + 6
So electrophiles likely to react at these positions

69
Q

What is 2,4 directing groups?

A

Electron donating

70
Q

Why do second substituted groups join at positoon 3 if the 1st substituted group is 2,4 directing?

A

Weaker position at 3

71
Q

What do side chains that decrease electron density do?

A

Slow electrophiles reactions compared to benzene so are “deactivating groups”

72
Q

Why is NO2 group a deactivating group?

A

O is more electronegative, drawing electrons away from delocalised ring
Withdraws electro density at positions 2,4 + 6
So electrophiles unlikely to react at these positions

73
Q

What is 3-directing groups?

A

Electron withdrawing

74
Q

Why do second substituted groups join at position 2,4/6 if the 1st substituted group is 3-directing?

A

Waeker positoon at 2,4 + 6

75
Q

What are the 2,4 directing groups?

A 
NH2
OH
OR
F, Cl, Br, I
R
76
Q

What are the 3-directing groups?

A

NO2
COOH
CHO
COOR

77
Q

Explain the relative resistance to bromination of benzene compared with alkenes

A

Benzene pi bond = delocalised
Alkene pi bond = localised
So alkenes have higher electron density compared to benzene
So benzene polarised Br2 LESS

A-Level Chemistry (26 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions