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A-level Chemistry > 27 - Aromatic chemistry > Flashcards

27 - Aromatic chemistry Flashcards

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1
Q

How are pi electrons organised in benzene?

A

Delocalised

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2
Q

What is benzene’s chemical formula?

A

C6H6

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3
Q

How long is a Benzene C-C bond? and how strong?

A

Between single and double C bond

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4
Q

What is benzene more thermodynamically stable than?

A

cyclohexa-1,3,5-triene

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5
Q

What is the increase in stability connected to delocalisation called?

A

Delocalisation energy

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6
Q

Why does benzene not undergo addition reactions?

A

This would break up the delocalised system

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7
Q

Why does benzene undergo electrophilic substitution?

A

High electron density

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8
Q

What is the electrophile in nitration?

A

NO2+

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9
Q

What condition(s) are needed for nitration?

A

Conc sulfuric acid
55C

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10
Q

What is nitration used to synthesise?

A
  • Explosives
  • Amines
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11
Q

What is the reaction to generate a nitronium electrophile?

A

Conc HNO3 + 2Conc H2SO4 goes to NO2+ + 2HSO4- + H3O+

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12
Q

What is the functional group change in Friedel Crafts acylation?

A

Benzene changes to phenyl ketone

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13
Q

What are the conditions for a Friedel Craft acylation?

A

Heat under reflux (50C)
Anhydrous aluminium chloride catalyst

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14
Q

What is the mechanism for a Friedel Craft acylation?

A

Electrophilic substitution

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15
Q

What is the electrophile for a Friedel Craft’s acylation?

A

RCO+

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16
Q

What is the equation for the formation of the electrophile in a Friedel Craft acylation?

A

AlCl3 + CH3COCl goes to [Ch3CO]+ + [AlCl4]-

17
Q

How can a nitroarene be reduced to an aromatic amine?

A

[H]
Heat, Sn and HCl
Forms water

Hydrogenation with H2 and Ni catalyst

18
Q

Explain the bonding in and the shape of a benzene molecule. Compare the stability of benzene with that of the hypothetical
cyclohexa-1,3,5-triene molecule, using thermochemical data given. (6)

A
  • Each Carbon has 3 covalent bonds
  • Spare electrons overlap
  • Delocalisation
  • Planar
  • 6 Carbon ring
  • C-C bond lengths between single and double bond
  • Expected hydrogenation of cyclohxatriene = -360
  • hydrogenation of benzene less exothermic by 152
  • Benzene more stable
19
Q

Why is minimum quantity of hot water used? (1)

A

Ensure hot solution is saturated with product

20
Q

Why is flask cooled to room temperature before crystals were fiiltered off?

A

Yield is lower if warm

21
Q

Why are crystals compressed in the funnel?

A

Air passes through sample not around it

22
Q

Why is a little cold water passed through crystals?

A

Remove insoluble impurities

A-level Chemistry (34 decks)

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