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1101 > AROMATIC CHEM > Flashcards

AROMATIC CHEM Flashcards

1
Q

Benzenoid hydrocarbons

A

ARENES

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2
Q

ARYL group

A

derived by removal of a H from the arene

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3
Q

PHENYL group unit

A

C6H5

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4
Q

BENZYL group unit

A

C6H5CH2

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5
Q

Benzene structure & bonding

A 
PLANAR HEXAGON
Delocalised pi e- cloud
120 
C-C equal lengths 140pm
sp2 C
More stable than predicted
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6
Q

Reactions of benzene

A

ELECTROPHILIC AROMATIC SUBSTITUTION

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7
Q

Describe the pathway of electrophilic aromatic substitution

A

E+ attacks - forms a partial bond with C.
WHELAND INTERMEDIATE (C formally bonded to E & H)
H leaves
Formal covalent bond to E+
LOWER ENERGY, THERMODYNAMICALLY FAVOURABLE PRODUCT.

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8
Q

WHELAND INTERMEDIATE

A

RESONANCE CONTRIBUTORS

Sigma complex

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9
Q

NITRATION of benzene

A

Warm with HNO3 & H2SO4 forms NITROBENZENE

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10
Q

generation of NO2+ ion

A

HNO3 + 2 H2SO4 NO2 + H3O+ + 2 HSO4-

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11
Q

Nitration mechanism

A

NO2+ attacks pi system, forms sigma-complex - loses a H+ -> NITROBENZENE.

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12
Q

SULFONATION conditions

A

Concentrated H2SO4 at 150 C

SO3 (E+)

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13
Q

Generation of SO3 (E+)

A

2 H2SO4 SO3 +H3O+ + HSO4-

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14
Q

What is unique about sulfation as an electrophilic substitution?

A

REVERSIBLE

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15
Q

Lewis Acid catalysts used for halogenation

A

AlCl3 or FeCl3 for chlorine

FeBr3 for bromine

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16
Q

IODINATION

A

via a DIAZONIUM SALT

or less commonly via oxidising agent

17
Q

Friedel-Crafts reaction

  • which catalyst type?
  • which mechanism?
  • comparing energy of reactants & products.
A

LEWIS ACID
ELECTROPHILIC AROMATIC SUBSTITUTION
Product more reactive than reactants

18
Q

Friedel Crafts alkylation precursors

A

alkyl halides, aliphatic alcohols, alkenes

19
Q

Compare stability of alkyl carbocations

A

TERTIARY more stable than METHYL

20
Q

Alkylation via alcohols

A

Benzene + alcohols -> carbocation formation via STRONG ACID

21
Q

Alkylation via alkenes

A

alkenes + arenes (+ catalyst) -> alkylbenzenes

22
Q

Friedel Crafts ACYLATION

A

Acid chlorides / anhydrides + (benzene via LEWIS ACIDS) -> KETONES

May also form alkyl derivatives

23
Q

Describe the mechanism of friedel crafts acylation

A 
ACYLIUM ION (E+) 
RESONANCE STRUCTURE

ELECTROPHILIC AROMATIC SUBSTITUTION

Via wheland intermediate

24
Q

compare alkylation & acylation speed

A

ACYLATION FASTER

25
Q

HUCKELS RULE

A

4n + 2

n = number of pi e-s

26
Q

HUCKELS RULE

A

4n + 2

n = number of pi e-s

1101 (8 decks)

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