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Y13 OCR A Organic Chemistry > 6.1.1 Aromatic Compounds > Flashcards

6.1.1 Aromatic Compounds Flashcards

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1
Q

What are arenes?

A

Aromatic compounds that contain a benzene ring

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2
Q

Structure of benzene

A

Ring of 6 carbon atoms each forming 3 sigma bonds to 2 other C atoms in the ring and an H atom (12 sigma bonds in total). The 4th electron of C is used to form a ring of 6 delocalised pi electrons. This makes benzene very stable

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3
Q

Evidence for benzene

A
  1. X ray studies show bond lengths are the same (between single and double bonds) and bond angles are the same
  2. Benzene does not decolourise bromine water (an alkene would)
  3. Benzene is more stable than expected (enthalpy of hydrogenation is a less negative number than expected)
  4. Benzene does not do electrophilic addition reactions like an alkene
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4
Q

Type of reaction benzene does

A

Electrophilic substitution

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5
Q

3 steps in electrophilic substitution of benzene

A
  1. Formation of electrophile using a catalyst
  2. substitution of benzene ring
  3. Regeneration of catalyst
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6
Q

Catalyst for halogenation

A

halogen carrier e.g. FeBr3 or AlCl3

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7
Q

Equation for formation of electrophile for bromination of benzene using AlBr3

A

Br2 + AlBr3 –> Br+ + AlBr4-

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8
Q

Mechanism for bromination

A
  1. pair of electrons from benzene ring attacks Br+
  2. Unstable intermediate formed (benzene ring with delocalised section from C1 to C5, C6 has C-H bond and C-Br bond, + charge in ring)
  3. curly arrow from C-H bond to reform ring
    (Practice drawing this separately)
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9
Q

Conditions for nitration of benzene

A

conc. H2SO4
conc. HNO3
50-55 oC

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10
Q

Electrophile for nitration of benzene

A

nitronium ion NO2+

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11
Q

Equation for formation of nitronium ion

A

HNO3 + H2SO4 –> NO2+ + HSO4- + H2O

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12
Q

Mechanism for reaction of benzene with nitronium ion

A

Check notes

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13
Q

Evidence that sulfuric acid is a catalyst in nitration of benzene

A

It is regenerated (not used up) HSO4- + H+ –> H2SO4

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14
Q

Overall equation for nitration of benzene

A

C6H6 + HNO3 –> C6H5NO2 + H2O

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15
Q

Overall equation for bromination of benzene

A

C6H6 + Br2 –> C6H5Br + HBr

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16
Q

Why is a low temperature needed for nitration of benzene

A

So only mono-substution occurs. Higher temperatures allow multiple substitutions e.g forming 1,3,5-trinitrobenzene

17
Q

Name of reaction between acyl chloride and benzene

A

Friedel-Crafts Acylation

18
Q

General formula of acyl chloride

A

RCOCl

19
Q

Equation for formation of electrophile in Friedel-Crafts acylation

A

RCOCl + AlCl3 –> RCO+ + AlCl4-

20
Q

Mechanism for Friedel-Crafts Acylation

A

Check notes

21
Q

Overall equation for Friedel-Crafts Acylation

A

C6H6 + RCOCl –> C6H5COR + HCl

22
Q

Product of Friedel-Crafts Acylation

A

phenylketone e.g. phenylethanone

23
Q

Observation in bromination of benzene

A

bromine decolourised and production of a white solid (bromobenzene)

24
Q

Test for an alkene

A

Decolourises bromine water

25
Q

What is a phenol

A

Compound containing a benzene ring with 1 OH group attached

26
Q

Acidity of phenol

A

Weak acid - will neutralise a strong base e.g. NaOH, will not react with a carbonate

27
Q

Method to tell apart phenol, ethanol and ethanoic acid including equations

A

Add NaOH and test pH. If no reaction has occurred and the pH is still 14, then ethanol. Phenol and Ethanoic acid will neutralise NaOH (pH7).
1. CH3COOH + NaOH –> CH3COO-Na+ + H2O
2. C6H5OH + NaOH –> C6H5O-Na+ + H2O
Add sodium carbonate to samples of phenol and ethanoic acid. The sample with effervescence is ethanoic acid.
3. 2CH3COOH Na2CO3 –> 2CH3COO-Na+ + H2O + CO2

28
Q

Comparison of electrophilic substitution reaction between benzene and phenol

A

phenol more reactive. A lp on O adds 2 more electrons to the delocalised ring making it more electron dense and more reactive. phenol reactions don’t need a catalyst and multiple substitutions are common
e.g. C6H5OH + 3Br2 –> 2,4,6-tribromophenol + 3HBr
The bromine water is decolourised and a white precipitate is seen

29
Q

Directing effects

A

OH and NH2 direct other electrophiles to 2 and 4 positions. NO2 directs to 3 position

Y13 OCR A Organic Chemistry (3 decks)

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