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CHEMISTRY > Organic - 3.10 Aromatic Chemistry > Flashcards

Organic - 3.10 Aromatic Chemistry Flashcards

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1
Q

What is the molecular formula of benzene?

A

C6H6

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2
Q

Does benzene decolourise bromine water?

A

No

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3
Q

What is the Mr of benzene?

A

78

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4
Q

What is the catalyst used in the hydrogenation of benzene?

A

A nickel catalyst

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5
Q

What does benzene form when it is hydrogenated?

A

Cyclohexane

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6
Q

What did Kekulé’s structure suggest about the bonds in benzene?

A

Alternating single and double bonds

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7
Q

How was Kekulé’s structure proved incorrect?

A

In 1922, bond angles were measured and it was found that all the carbon carbon bonds were the same length, at an intermediate value between that of C-C and C=C, suggesting Kekulé was incorrect.

Kekulé’s Benzene structure has three C=C bonds so it would be expected to have an enthalpy change of -360 however when benzene is hydrogenated the enthalpy change is only -208. This means that the actual structure of benzene is more stable than the Kekulé structure .

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8
Q

What is the enthalpy of hydrogenation?

A

The enthalpy change when one mole of an unsaturated compound reacts with an excess of hydrogen to become fully saturated

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9
Q

What is the shape of todays model of benzene?

A

Planar hexagonal

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10
Q

What is the length of the bonds in todays model of benzene?

A

Intermediate length between that of C-C and C=C

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11
Q

How does the ring of delocalised electrons form in the benzene ring?

A

Each carbon uses three of its outer electrons to form three sigma bonds to two other carbon atoms and one hydrogen atom. This leaves each carbon at with one electron in a P orbital

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12
Q

What is the bond angle in todays model of benzene?

A

120

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13
Q

What does the circle represent in the structure of benzene?

A

The ring of delocalised electrons

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14
Q

What are arines?

A

Aromatic hydrocarbons that contain one or more benzene rings

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15
Q

What is the state of arines at room temperature?

A

Colourless liquid

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16
Q

Why is benzene immiscible in water?

A

It is non-polar

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17
Q

Why does benzene not decolourise bromine water?

A

It doesn’t undergo addition reactions due to stable delocalised electron ring

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18
Q

Why does cyclohexene decolourise bromine water?

A

Cyclohexene contains a reactive double bond which undergoes addition reaction.

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19
Q

What type of reaction does benzene undergo?

A

Electrophilic substitution

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20
Q

How is a benzene derivative formed?

A

If one of the hydrogen atoms on a benzene ring is replaced by an atom or group

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21
Q

How is an alkyl group formed?

A

Alkyl groups are formed by removing a hydrogen atom from an alkane

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22
Q

How is a phenyl group formed?

A

Removing a hydrogen group from a benzene ring

23
Q

Why is benzene attacked by electrophiles?

A

There is a region of higher electron density above and below the plane of the molecule

24
Q

Why do substitution reactions occur rather than addition reactions?

A

Substitution reactions occur rather than addition reactions as this preserves the stability of the benzene ring

25
Q

What happens in the nitration of benzene?

A

The hydrogen atom on the ring is replaced by a nitro group

26
Q

What is the electrophile in the nitration of benzene?

A

Nitronium ion

27
Q

What are 3 uses of nitrated arines?

A

1) manufacture of explosives
2) nitrobenzene can be reduced to phenylamine(dyes)
3) organic synthesis

28
Q

What is acylation?

A

The process of replacing a hydrogen atom in certain molecules by an Acyl group

29
Q

What is the catalyst used in benzene acylation?

A

Aluminium chloride

30
Q

What is the catalyst used in benzene nitration?

A

Concentrated sulfuric acid

31
Q

What is formed from the acylation of benzene?

A

An aromatic ketone

32
Q

What is the reagent in the nitration of benzene?

A

Concentrated sulfuric acid and concentrated nitric acid

33
Q

What are the conditions for the nitration of benzene?

A

50°C

34
Q

What happens in the nitration of benzene?

A

Hydrogen atom on the ring is replaced by a nitro group

35
Q

What are the products in the nitration of benzene?

A

Aromatic nitro compounds

36
Q

What is the overall equation for the nitration of benzene?

A

C6H6 + HNO3 -> C6H6NO2 + H2O

37
Q

What is the equation for the generation of the electrophile in the nitration of benzene?

A

HNO3 + 2H2SO4 -> NO2+ + 2HSO4- + H3O+

Forms a nitronium ion

38
Q

What is the reagent in the acylation of benzene?

A

Acyl chloride or acid anhydride & AlCl3

39
Q

What are the conditions for the acylation of benzene?

A

Anhydrous

40
Q

What happens in the acylation of benzene?

A

Hydrogen atom on the ring is replaced by an acyl group

41
Q

What are the products in the acylation of benzene?

A

Aromatic ketones

42
Q

What is the overall equation for the acylation of benzene?

A

C6H6 + RCOCl -> C6H5COR + HCl

43
Q

What is the equation for the generation of the electrophile in the acylation of benzene? (Acyl Chloride)

A

RCOCl + AlCl3 -> RCO+ + AlCl4+

44
Q

What is the equation for the generation of the electrophile in the acylation of benzene? (Acid Anhydride)

A

RCOOCOR + AlCl3 -> RCO+ + [Cl3AlOCOR]-

45
Q

What is the equation for the regeneration of the catalyst in the acylation of benzene? (Acyl Chloride)

A

AlCl4- + H+ -> AlCl3 + HCl

46
Q

What is the equation for the regeneration of the catalyst in the acylation of benzene? (Acid Anhydride)

A

[Cl3AlOCOR]- + H+ -> AlCl3 + HOCOR

47
Q

What is an addition reaction?

A

A reaction in which molecules combine to form a single product

48
Q

What is an addition reaction?

A

A reaction in which molecules combine to form a single product

49
Q

What is an aromatic compound?

A

A compound containing at least one benzene ring

50
Q

What is an electrophile?

A

An electron pair acceptor

51
Q

What is electrophilic substitution?

A

A reaction in which an electrophile replaces an atom/group of atoms in a compound.

52
Q

What is Friedel-Crafts Acylation?

A

An important synthetic reaction involving an electrophilic aromatic substitution reaction between benzene and Acyl chlorides or anhydrides, used to form monoacylated benzene rings. AlCl3 is used as a catalyst.

53
Q

What is nitration?

A

Benzene undergoes nitration via an electrophilic substitution reaction, using concentrated nitric acid and a concentrated sulfuric acid catalyst at 50 degrees.

54
Q

What is a substitution reaction?

A

A reaction in which one atom/group of atoms is replaced by another atom/group of atoms.

CHEMISTRY (34 decks)

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