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Mpharm 1 COPY > PH1125 - Aromatics > Flashcards

PH1125 - Aromatics Flashcards

1
Q

what is the structure of aromatics? (3)

A
  • each C atom is sp2 hybridised in a planar ring
  • each c atom has one hydrogen atom attached to it
  • each C atom has an unhybridised p orbital perpendicular to the planne of the sigma bond of the ring
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2
Q

what is the name of benzene and OH group attached?

A

phenol

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3
Q

what is the name of benzene and NH2 group attached?

A
  • aniline
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4
Q

what is the name of benzene and COOH group attached?

A
  • benzoic acid
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5
Q

what is the name of benzene and CH3 group attached?

A
  • toluene
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6
Q

what are the four requirements for aromaticity? (4)

A
  • cyclic
  • planar
  • conjugated (complete overlap of p orbitals)
  • (4n+2) pi electrons

if a system doesnt fit the criteria there cannot be complete delocalisation of the pi electrons

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7
Q

to be aromatic why must a molecule have all pi electrons paired? (2)

A
  • this gives the maximum and complete overlap required for aromatic stabilisation
  • if overlap is not maximised some orbitals are not filled and the compound is not aromatic
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8
Q

what is SEAR? (2)

A

monosubstitution

  • electrophilic aromatic substitution
  • reactions in which an electrophile is substituted for one of the H atoms on the ring
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9
Q

how do you get from benzene to benzonium ion? (2)

A
  • lewis acid as a catalyst (which reacts with the reagent to generate the electrophile)
  • the pi electrons of the benzene ring attack the electrophile to form a resonance stabilised carbocation
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10
Q

how do you get from benzonium ion to a product (benzene and electrophile on ring)?

A
  • reacts further to lose a H+ ion from the intermediate to form the product
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11
Q

what happens in SEAR halogenation? (4)

A
  • X+ collides with the electrons of the aromatic pi cloud
  • a pair of electrons form a sigma bond with the electrophile
  • benzenonium ion loses a proton to a base in the reaction mixture
  • the final step is the regeneration of the lewis acid
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12
Q

what happens in SEAR nitration? (2)

A
  • electrophile is the nitronium ion (to form nitrobenzene)

- H2SO4 catalyst is used

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13
Q

what happens in SEAR friedel crafts alkylation?

A
  • reaction of the alkyl halide with AlCl3 to make the electrophile which is a carbocation
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14
Q

what happens in SEAR friedel crafts acylation?

A
  • reaction of the acyl halide with AlCl3 to make the electrophile which is an acylium ion
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15
Q

what does the rate at which a second substitution occur depend on?

A
  • the substrate being added
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16
Q

what happens when activating groups are added to a benzene ring?

A
  • undergoes SEAR a lot faster

- no catalyst needed

17
Q

what happens when deactivating groups are added to a benzene ring?

A
  • undergoes SEAR a lot slowe

- requires long reaction time and catalyst

18
Q

what does the position of the second substitution depend on?

A
  • it is determined by the group already on the ring
19
Q

what are examples of electron donating (activating) groups? (6)

A
  • NH2, NHR, NR2
  • OH
  • OR
  • aryl
  • alkyl
  • halide
20
Q

what are examples of electron withdrawing (deactivating) groups? (6)

A
  • COR
  • CO2R
  • SO3R
  • CHO
  • CN
  • NO2

electron withdrawing reduced nucleophilicity

21
Q

how do halogens deactivate aromatic rings?

A
  • by its electron-withdrawing inductive effects
22
Q

what is SNAR?

A
  • nucleophilic aromatic substitution
23
Q

what undergoes SNAR?

A
  • under certain conditions aryl halides undergo SNAR reactions
24
Q

how is a benzene with nucleophile attached formed using an aryl halide? (2)

A
  • the reactivity of aryl halides towards nucleophiles are enhanced by the presence of electron-withdrawing substituents on the ring
25
Q

what does an electron-withdrawing group do to a ring? (2)

A
  • makes the ring less rich in electrons and pulls electrons away from the ring system
  • therefore more attractive to an attacking nucleophile
26
Q

how do you get from chlorobenzene to phenol? (3)

A
  • 10% NaOH
  • 350 degrees
  • 300 atm of pressure

Mpharm 1 COPY (59 decks)

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