6.1.1 - Aromatic compounds Flashcards

1
Q

Arenes

A

Aromatic molecules containing 1 or more benzene rings

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2
Q

-OH

A

Hydroxy -

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3
Q

NO2

A

Nitro -

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4
Q

F

A

Fluoro -

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5
Q

NH2

A

-amine

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6
Q

Benzoic acid

A

Benzene ring attached to COOH group

Acid group is always highest priority (1’ priority)

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7
Q

Phenyl -

A

Prefix if attached to an akyl chain w/ more than 6 carbons OR w/ a carbon chain w/ a functional group

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8
Q

Kekule structure

A

Benzene is v. reactive

Diff C-C bond lengths

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9
Q

Problems w/ Kekule’s structure

A

C-C bonds are all same lengths
Benzene does not undergo addn. reactions readily (resistance to reaction)
Enthalpy of hydrogenation 152kJ/mol less exothermic than expected

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10
Q

Delocalised electrons

A

Electrons shared between more than two atoms

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11
Q

Which model of benzene do we use now

A

Delocalised model

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12
Q

Using a labelled diagram. disprove Kekule

A

p-orbitals overlap sideways —> Delocalised pi-system above and below
Planar carbon ring
All bonds 120 degrees

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13
Q

Why do electrophiles react more easily w cyclohexane than w/ benzene

A

In benzene, pi-electrons are delocalised
In cyclohexane, the pi-electrons are localised
So benzene has a lower electron density
And so benzene polarises the electrophile less

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14
Q

Priorities

A

COOH>…> hydrocarbons > F,Cl,Br,I> NO2

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15
Q

How did the scientist disprove Kekule

A

Using diffraction to find the carbon-carbon lengths

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16
Q

Why does phenol react more readily w/ electrophiles then benzene does

A

Lone pair from -OH group in phenol is drawn into the delocalised benzene ring
so electron density increases
and the electrophile is more strongly attracted

17
Q

Electron donating groups

A

-OH
-NH2
-CH3
2 (6),4 directing

18
Q

Electron withdrawing groups

A

-NO2
-COOH
3’, (5) directing
Less reactive so only one substitution

19
Q

Why is bromine not attracted to benzoic acid

A

-COOH is an electron withdrawing group
therefore pi-system becomes less dense
and will not attract electrophiles as strongly

20
Q

Electrophilic substitution w/ bromine and phenols

A

White ppt

Decolourises bromine water

21
Q

Nitration of benzene (nitrobenzene)

A

HNO3
H2SO4 (Conc. catalyst)
50 degrees

HNO3 + H2SO4 —> NO2^+ + HSO4 ^- + H2O
H+ + HSO4^- –> H2SO4

22
Q

Dinitrobenzene

A

2 HNO3
Conc. H2SO4
70 degrees

23
Q

Bromination of benzene

A

Occurs at RTP (electrophilic subsitution) in the presence of a halogen carrier
Overall: C6H6 + Br2 –> C6H5Br + HBr
Br2 + FeBr3 —> FeBr4^- + Br^+
H^+ + FeBr4^- —> FeBr3 + HBr

24
Q

General formula for electrophilic substitution w/ benzene

A

AX + C6H6 —> C6H5A + HX
A - Electrophile
X - halogen

25
Q

Halogen carriers

A

Benzene is non polar and so needs a halogen carrier to gnerate an electrophile e.g. FeBr3/AlBr3

26
Q

The higher the elctronegativity …

A

The more the electrophile

27
Q

Why isn’t phenol v. soluble

A

Non polar benzene ring

28
Q

What does phenol dissociate into

A

Phenoxide ion and H^+

29
Q

Reactions w/ phenol

A

Only strong bases (no carbonates)
Reactive metals e.g. Na
Br2 –> 2,4,6 tribromophenol

30
Q

Functional group priorities

A
-COOH (oic acid)
ester (-oate)
acid chloride (-oyl chloride)
-amide
A,K,A
-amine
31
Q

Tests for phenol

A

pH paper and Na2CO3 (aq) - pH paper turns red, no reaction
FeCl3 (aq) in NH3 sol. - solution turns purple
Bromine water - decolourises, white ppt may form

32
Q

Phenol w/ dilute vs conc HNO3

A

One substitution vs 3 substitutions