aromatic chemistry Flashcards

1
Q

what is aromatic chemistry

A

the study of benzene and compounds containing the benzene ring

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2
Q

what are compounds containing the benzene ring called

A

arenes

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3
Q

evidence against the kekule structure of benzene

A
  • benzene doesn’t decolourise bromine water (whereas c=c does)
  • carbon carbon bond lengths (C=c shorter than C-C)
  • thermochemical data for the hydrogenation of benzene suggests that more stable than the kekule structure
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4
Q

justfifcation for c-c bond lengths in benzene

A

bond lengths intermediate- benzene is a regular hexagon- if bonds single double alternating would be irregular

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5
Q

how does thermochemical data for hydrogenation of benzne suggest its more stable than expected

A

enthalpy is roughly 150kJ/mol more stable than expected

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6
Q

what structure does benzene have

A

a regular, planar, hexagon structure

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7
Q

why does benzene have a regular planar hexagon structure

A

the six c atoms and the six h atoms are all in the same plane

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8
Q

what are all bond angles in benzene

A

120 degrees

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9
Q

how are the 6 c-c bond intermediate in length

A

between length of a c-c and a c=c bond

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10
Q

how does the pi bond form

A

overlap of adjacent p orbitals

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11
Q

where does the pi bond form

A

above and below the ring

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12
Q

what is the pi bond essentially

A

an electron cloud above and below the ring

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13
Q

where are elections In the pi bond

A

delocalised

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14
Q

why are the pi bonds in benzene harder to break than a normal c=c bond

A

the delocalised structure has extra stability

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15
Q

which part of the benzene ring attracts electrophile

A

the pi bond above and below the plane

is an area of moderately high electron density

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16
Q

electrophile

A

an electron pair acceptor

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17
Q

what happens in the electrophilic substitution reaction of benzene

A

a h atom from the benzene ring is replaced by a new group of atoms

18
Q

why does benzene undergo substitution rather than addition

A

to preserve the stability of the delocalised pi bond

19
Q

nitration:reagents

A

conc sulphuric and conc nitric

sulphuric is catalyst

20
Q

nitration: conditions

A

below 50 degrees Celsius

21
Q

nitration: overall equation

A

benzene+ nitric > nitrobenzene + water

22
Q

nitration: electrophile

A

nitronium ion NO2+

23
Q

nitration: generation of electrophile equation

A

H2SO4 + HNO3 > NO2+ + HSO4- + H2O

24
Q

nitration: regeneration of catalyst

A

H+ + HSO4- > H2SO4

25
acylation: reagents
acyl chloride
26
acylation: conditions
AlCl3 (halogen carrier) and heat
27
acylation: general equation
benzene + acyl chloride > (benzene)-COR + HCl
28
acylation: electrophile
RCO +
29
acylation: benzene + ethanoyl chloride | generation of electrophile
CH3COCl + AlCl3 > CH3CO+ + AlCl4-
30
acylation: benzene + ethanoyl chloride | regeneration of catalyst
AlCl4- + H+ > AlCl3 + HCl
31
reaction mechanism cyclohexene and bromine
electrophilic addition
32
reaction mechanisms benzene and bromine
electrophilic substitution
33
why are the reactions different: benzene
- delocalised pi bonds - lower electron density - need to generate Br+ for the reaction to occur
34
why are the reactions different: cyclohexene
- localised pi bonds - greater electron density - able to induce dipole in Br2
35
why is methyl benzene more reactive than benzene with electrophiles
- CH3, through positive inductive effect, provides more electron density - increases electron density of delocalised pi bond - methyl benzene better at attracting electrophiles
36
why is the nitration of benzene an important reaction
nitrogen containing aromatic compounds have many applications
37
uses of nitrobenzene
explosives
38
reagents for nitration of benzene
conc nitric and conc sulphuric
39
uses of benzene with -NH2 group attached (amine)
dyes and drugs
40
how to get from nitrobenzene to benzene with an -NH2 group (amine)
conc hydrochloric | tin catalyst
41
what can nitrobenzene be reduced to form
amine
42
equation for reduction of aromatic nitro compounds
benzene-NO2 + 6[H] > benzene-NH2 + 2H2O