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The final mock (Chem) > Unit 4.2 Aromaticity (Sweet B|) > Flashcards

Unit 4.2 Aromaticity (Sweet B|) Flashcards

1
Q

Define cyclic

A

Ring-shaped

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2
Q

Define planar

A

Flat

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3
Q

Describe “aromaticity”
(4-way)

A
  • Cyclic & planar molecule
  • w/ ring of resonance bonds
  • exhibiting more stability than other “arrangements”
  • with same set of atoms
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4
Q

Define arenes

A

Ring structures

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5
Q

Define carcinogen
(2-way)

A
  • Chemical/agent
  • that can potentially cause cancer
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6
Q

Describe benzene
(2-way)

A
  • Colourless & flammable liquid
  • Has sweet & gasoline-like odour
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7
Q

How can benzene (useful chemical substance) be toxic?
(2-way)

A
  • A carcinogen
  • Continuous exposure = cancerous effects
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8
Q

5 key facts of Benzene
(3 of em are pretty imp)

A
  • C6H6
  • Planar
  • 3 C=C (π) double bonds & 3 C-C (σ) single bonds
  • Hexagonal ring
  • Trigonal planer about each carbon
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9
Q

Draw the 2 versions of benzene

A

Stage is yours

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10
Q

What does the circle in 1 benzene variation represent?
(2-way)

A
  • 3 π bonds
  • aka 6 π e-
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11
Q

2 compounds that are aliphatic?

A
  • Alkane
  • Alkene
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12
Q

How do arenes differ with aliphatics?
(2-way)

A
  • They possess 1/more rings of carbon atoms
  • Bonding electrons are delocalised
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13
Q

Explain the structure of benzene pt. 1
(3-way)

A
  • Normal sigma bond
  • Formed between each pair of carbons
  • Each containing 2 electrons
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14
Q

Explain the structure of benzene pt. 2
(3-way)

A
  • Remaining 6 electrons (1 from each carbon)
  • Occupy p-orbitals
  • Which they overlap to form a π bond
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15
Q

Hence, draw the explanation of the structure of benzene

A

Stage is yours

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16
Q

3 consequences of benzene and its delocalisation of some bonding electrons?

A
  1. Benzene much more stable than expected
  2. Extra stability = benzene less readily undergo addition reactions
  3. More loosely held electrons = open to attack by electrophiles
    electrophilic substitution type shi
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17
Q

Explain “1.” Benzene much more stable than expected as a consequence?
Pt. 1
(2 inf, 1 + 2-way)

A
  • Actual enthalpy of formation of benzene = 82 kJmol-1
  • Enthalpy of hydrogenation of cyclohexene (C6H10) = -120 kJmol-1
  • Cyclohexene contains 3 alkene double bonds
  • ∴ expected enthalpy of hydrogenation to cyclohexene
  • to be “3x”, -360 kJmol-1
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18
Q

Explain “1.” Benzene much more stable than expected as a consequence?
Pt. 2
(4-way)

A
  • Ended up being -210 kJmol-1
  • Difference between expected and actual value = 150 kJmol-1
  • Hence, that’s the stabilisation energy (delocalisation energy) of benzene
  • Explains why it’s resistant to addition reactions
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19
Q

2 aromatic properties of benzene?

A
  1. Resistance to addition
  2. Electrophilic substitution
20
Q

Explain resistance to addition of benzene?
And draw an eqn showing that.

A
  • Extra stable due to delocalistion
  • Stage is yours:
    Benzene + X2 -> Hexagon w/ 2 lines inside and 2 other bonds with X
    which btw, isn’t impossible….
21
Q

Explain electrophilic substitution of benzene?
And draw and eqn showing that.

A
  • Characteristic reaction of benzene is electrophilic substitution
  • Stage is yours pal:
    “Benzene”-H + Br2 -> “Benzene”-Br + HBr
22
Q

What else is a must for benzene to undergo electrophilic substitution?

A

Use of a halogen carrier

23
Q

Name of Benzene containing OH group?

A

Phenol
(Hydroxybenzene)

24
Q

How is phenol more reactive than benzene?
(4-way)

A
  • Oxygen lone pair donated
  • into ring system
  • Increases electron density
  • Hence… voila
25
Q

If phenol more reactive than benzene, what’s a “pro” for that?
(True 2-way)

A
  • No halogen carrier needed
  • For electrophilic substitution
26
Q

Name of benzene containing CH3 group?

A

Methylbenzene
(Toluene)

27
Q

Methylbenzene is also more reactive than benzene, but how so?
(4-way)

A
  • No lone pair
  • BUT, from bonded electrons in CH3
  • Donating additional e- density into ring
  • Hence, increases reactivity
28
Q

What are the 4 different reactions that can take place w/ benzene?

A
  1. Nitration of Benzene
  2. Friedel-Crafts alkylation of Benzene
  3. Friedel-Crafts acylation of Benzene
  4. Halogenation of Benzene
29
Q

What is required for 1. Nitration of Benzene?
(2 things)

A
  • Reflux w/ conc. HNO3 + H2SO4
  • Must be below 55°C
30
Q

Why must reaction be below 50°C?
(1. Nitration of Benzene)

A

To avoid further substitution onto the ring

31
Q

Draw mechanism of Nitration of Benzene

A

The #1 stage is yours

32
Q

Which part of mechanism is slow (RDS)
(1. Nitration of Benzene)

A

+ NO2+ part

33
Q

Which part of mechanism is fast?
(1. Nitration of Benzene)

A

H going into Benzene part

34
Q

What is required for 2. Friedel-Crafts alkylation of Benzene?
(2 things)

A
  • Req. formation of alkyl cation e.g. CH3Cl
  • Req. halogen carrier e.g. AlCl3
35
Q

Draw mechanism of Friedel-Crafts alkylation of Benzene

A

The #2 stage is yours

36
Q

What is required for 3. Friedel-Crafts acylation of Benzene?
(2 things)

A
  • Req. acyl group e.g. R-C(=O)R1
  • Req. halogen carrier (just like 2nd typa rxn)
37
Q

Draw mechanism of Friedel-Crafts acylation of Benzene

A

The #3 stage is yours

38
Q

What is required for 4. Halogenation of Benzene?
(2 things)

A
  • Req. just the halogens e.g. Cl2
  • Req. specific catalyst for the halogen e.g. AlCl3
39
Q

Draw mechanism of Halogenation of Benzene

A

The final #4 stage is yours

40
Q

How to name aromatic compounds with single substituents?
(3-way, chill guy type)

A
  • Prefix of such group
  • Attach to word benzene
  • e.g. Chlorobenzene or Methylbenzene or Nitrobenzene
41
Q

How to name aromatic compounds with multiple substituents of the same type?
(4-way, such chill)

A
  • Number at the beginning based on pos.
  • Additional prefix too
  • & w/ single substituents naming
  • e.g. 1, 3 - dichlorobenzene
42
Q

How to name aromatic compounds with multiple substituents of different types?
(4-way, what a chill guy)

A
  • Number first based on pos.
  • Additional prefix BUT for one that’s multiple
  • Then single substituent of such
  • VOILA! e.g. 2,4,6 - trichlorophenol or 2,4,6 - trinitromethylbenzene
43
Q

What’s the arylchloride?

A

Ring bonded w/ Cl

44
Q

What’s the alkylchoride?

A

Straight chain bonded w/ Cl

45
Q

How is Arylchloride > Alkylchloride in terms of bond strength?
(2-way + 3 instances)

A
  • Due to lone pair of e- arylchloride
  • perp. to plane of molecule
  • Delocalised into π-e- system of ring
  • Bond = stronger + shorter
  • Less able to be replaced by nucleophiles
46
Q

Congrats on revamping this, now the stage really is yours

A

… in 4 days??

The final mock (Chem) (9 decks)

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