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Chemisty A level > Aromatic Chemistry > Flashcards

Aromatic Chemistry Flashcards

1
Q

What is a aromatic compound?

A

a compound containing a benzene ring

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2
Q

What is an arene?

A

an aromatic hydrocarbon

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3
Q

What proves the kekule formula of benzene to be wrong?

A
  1. benzene doesnt easily undergo addition reactions of alkenes
  2. all the bond lengths between C atoms are the same length
  3. hydrogenation of benzene is less exothermic than expected
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4
Q

What happens during a reaction between benzene and Br2?

A

doesnt declourise bromine
reacts with a presence of a catalyst by substitution

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5
Q

What does hydrogenation of benzene being less exothermic suggest?

A

the pi bonds in benzene are more stable than expected

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6
Q

What shape molecule is benzene?

A

a planar molecule

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7
Q

How is a delocalised pi system formed in benzene?

A

each C atom has 1 electron in a p orbital - these orbitals overlap above and below the carbon ring

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8
Q

Why does benzene have a low reactivity?

A

delocalisation spreads out the pi-electrons so there is a lower electron density making them less attractive to electrophiles

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9
Q

Why are benzene’s bond lengths all equal?

A

the pi-electrons are distributed evenly around the ring

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10
Q

What is nitration?

A

the introduction of a nitro group - NO2

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11
Q

What are the conditions of nitration with benzene?

A

conc nitric acid and conc sulfuric acid

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12
Q

How is an electrophile of NO2 + formed by sulfuric acid? (equation)

A

HNO3 + H2SO4 <—–> NO2+ + H2O + HSO4-

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13
Q

What is eliminated from a electrophilic subsititution with benzene?

A

H+

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14
Q

What must be present for halogenation of benzene to take place?

A

a halogen carrier eg: AlCl3

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15
Q

What is the kekule model?

A

it demonstrates the double bonds present in benzene but doesnt consider the delocalised pi system

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16
Q

Why are aromatic compounds less reactive than alkenes?

A

delocalisation - there is a lower pi electron density in the aromatic ring so electrophiles are less strongly attracted

17
Q

How do aromatic compunds react differently with electrophiles than alkenes with electrophiles?

A

aromatics react by substitution whereas alkenes react by addition

18
Q

What is electrophilic substitution?

A

a chemical reaction in which the functional group attacged to a compound is replaced by an electrophile

19
Q

What is the equation of the regeneration of the catalyst H2SO4?

A

(HSO4 -) + (H+) —–> H2SO4

20
Q

What is observed when reacting benzene with bromine?

A

the bromine decoloursies - orange to colourless and steamy fumes of HBr are produced

21
Q

What is the reversible reaction between Br2 and its halogen carrier?

A

Br2 + AlBr3 <—–> (Br+) + (AlBr4-)

22
Q

What is the equation of the regeneration of the catalyst AlBr3?

A

(H+) + (AlBr4-) —–> AlBr3 + HBr

23
Q

What happens in terms of bonding during an addition reaction?

A

replaces the pi bonding with new sigma bonds

24
Q

How can an alkyl group be attached to a benzene?

A

electrophilic substitution with a halogen carrier forming an alkyl electrophile

25
Q

What is the reversible reaction between CH3CH2Cl and AlCl3 to form the alkyl electrophile?

A

CH3CH2Cl + AlCl3 <—–> (CH3CH2+) + (AlCl4-)

26
Q

Why are reactions with benzene and an alkyl group important?

A

important in organic synthesis to form C-C bonds and allows an organic molecule to be extended

27
Q

What is the name for a benzene ring attached to another molecule?

A

a phenyl group

28
Q

What is a aliphatic molecule?

A

any compound that doesnt contain a benzene ring

29
Q

What does alicyclic mean?

A

any aliphatic (non-aromatic) compound that contains a ring

30
Q

What is protonation?

A

adding of a proton ususally donated by H+ to an atom, molecule of ion

31
Q

What is alkylation?

A

adding an alkyl group to a benzene

32
Q

What is acylation?

A

adding an acyl group to a benzene
(carbonyl)

33
Q

What is an acyl group?

A

a carboxylic acid functional group with a Cl instead of OH = a carbonyl - aldehyde or ketone

34
Q

How many sigma bonds are present in benzene?

A

12
each C atom is bonded to another C and a hydrogen

35
Q

How many delocalised electrons are in the delocalised pi system of benzene?

A

6

36
Q

What is the molecular formula of benzene in its simplist form?

A

CH

37
Q

How can you form cyclohexane from benzene?

A

hydrogenation - H2 and Ni catalyst

38
Q

What state is bromine in to react with benzene?

A

liquid

39
Q

Why is hydrogenation of benzene less exothermic than expected?

A

the pi system makes benzene more stable = more energy needed to break bonds

Chemisty A level (28 decks)

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