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A Chem Finale pt 1. > Unit 4.2 Aromaticity (og) > Flashcards

Unit 4.2 Aromaticity (og) Flashcards

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1
Q

Describe the term aromaticity

A
  • Cyclic (ring-shaped)
  • Planar (flat)
  • Molecule with a ring of resonance bonds that exhibits more stability than other geometric or connective arrangements with the same set of atoms

^what da faq

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2
Q

What are arenes?

A

Ring structures

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3
Q

What is Benzene?

A
  • A liquid
  • Colourless
  • Flammable
  • Sweet and gasoline-like odour
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4
Q

How can Benzene (a useful chemical substance) be toxic?

A
  • Continuous exposure = cancerous effects
  • It’s a carcinogen
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5
Q

What is a carcinogen?

A

Chemical/agent that can potentially cause cancer

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6
Q

Describe 5 key facts of Benzene?

A
  • C6H6
  • Planar
  • Contains 3 C=C (π) double bonds and 3 C-C (σ) single bonds
  • Hexagonal ring
  • Trigonal planar about each carbon
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7
Q

Must learn how to draw benzene
…
and perhaps acknowledge it’s 3 other representations

A

Sweet
….
yayaya

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8
Q

What does the circle within benzene represent?

A

3 π bonds
aka
6 π e-

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9
Q

What are aliphatic compounds?

A

Alkanes and alkenes

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10
Q

How can arenes (benzene) differ from aliphatic compounds (alkanes and alkenes)?

A
  • Possess one/more rings of carbon atoms
  • Bonding electrons are delocalised

That’s why I said benzene in brackets

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11
Q

Show me how benzene differ from alkanes or alkenes

(pretty much explains the circle inside hexagon)

A
  • Normal sigma bond (standard covalent bond)
  • Formed between each pair of carbons
  • Each containing 2 electrons
    BUT THEN
  • Remaining 6 electrons (1 from each carbon)
  • Occupy p-orbitals
  • Which they overlap to form a π bond

In Benzene’s case, bond extends over all 6 carbon atoms

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12
Q

What are 3 consequences of Benzene’s delocalisation of some of the 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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13
Q

Explain the consequence of Benzene being much more stable than expected

A
  • Actual enthalpy of formation of benzene = 82 kJmol-1
    (Enthalpy of Hydrogenation experiments)
  • Enthalpy of Hydrogenation of cyclohexene is -120 kJmol-1
    ^^ feel like kinda useless? Perhaps know just the top right?
  • Contained 3 alkene double bonds ∴ expected enthalpy of hydrogenation to cyclohexane to be 3x -360kJmol-1
  • Ended up being -210 kJmol-1
  • Difference between 2 values = 150 kJmol-1
    And is therefore the stabilisation energy (delocalisation energy) of benzene

EXPLAINS WHY IT’S RESISTANT TO ADDITION REACTIONS

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14
Q

2 aromatic properties of Benzene?

A
  1. Resistance to addition
    (Extra stable due to delocalisation)
  2. Electrophilic substitution
    (Characteristic reaction of benzene is electrophilic substitution)
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15
Q

How will Benzene only undergo electrophilic substitution?

A

The use of a halogen carrier

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16
Q

What do u call benzene that contains an OH group?

A

Phenol
(hydroxybenzene)

17
Q

2 significant difference between Phenol and Benzene?

A
  • Phenol more reactive than Benzene
  • No assistance undergoing electrophilic substitution
    (Lone pairs of O2 will overlap with delocalised ring system)
    Refer to booklet D:
18
Q

What do u call benzene that contains Methyl group?

A

Methylbenzene
(Toluene)

19
Q

Significant difference between Methylbenzene and Benzene?
(Same as with Phenol)

A
  • More reactive than Benzene
20
Q

State all the reactions of Benzene

A
  1. Nitration of Benzene
  2. Friedel-Crafts alkylation of Benzene
  3. Friedel-Crafts Acylation of Benzene
  4. Halogenation of Benzene
21
Q

You must learn how to draw all the reactions of Benzene

A

It’ll take a while….

22
Q

Explain nitration of Benzene?

A

Err

23
Q

Explain Friedel-Crafts alkylation of Benzene?

A

Uhh

24
Q

Explain Friedel-Crafts acylation of Benzene?

A

Umm

25
Q

Explain halogenation of Benzene?

A

Erm

26
Q

3 types of naming aromatic compounds?

A
  • Single Substituents
  • Multiple Substituents of the Same Type
  • Multiple Substituents of Different Types
27
Q

Benzene with CH3 connected?

A

Methylbenzene

28
Q

Benzene with Cl connected?

A

Chlorobenzene

29
Q

Benzene with CH2CH3 connected?

A

Ethylbenzene

30
Q

Benzene with NO2 connected?

A

Nitrobenzene

31
Q

Benzene but 2 Cl’s connected bottom left & right?

A

1, 3 - dichlorobenzene

32
Q

Benzene but CH3 diagonal parallel to each other or summin?

A

1, 4 - dimethylbenzene

33
Q

Benzene but 3 Br’s above and bottom left & right?

A

1, 3, 5 - tribromobenzene

34
Q

Benzene but Cl bottom right & CH3? (nothing is there) bottom right?

A

3 - chloromethylbenzene

35
Q

Benzene but OH above and 3 Cl’s bottom, top left & right?

A

2 names:
- 2, 4, 6 - trichlorohydroxybenzene
- 2, 4, 6 - trichlorophenol aka TCP

36
Q

Benzene but NO2 bottom, top left & right and CH3? (nothing is there) above?

A

2 names:
- 2, 4, 6 - trinitromethylbenzene
- 2, 4, 6 - trinitrotoluene aka TNT

37
Q

Show me the strength difference of Cl-C bonds?

A

Arylchloride > alkylchloride

38
Q

What do you think is the reason for the Cl-C bond in chlorobenzene being stronger than the Cl-C bond in 1-chloropropane?

A
  1. Draw both of them first
  2. A lone pair of electrons in a p-orbital on the Cl that is perpendicular to the plane of the ring will delocalise into the π-ring system. This means the C-Cl bond in the arychloride is shorter AND stronger than the corresponding C-CL bond in the alkyl chloride
  3. Draw the nucleophilic substitution ig?
39
Q

Still much to learn, especially them mechanisms. U needa do questions too.

A

I’m just hungry

A Chem Finale pt 1. (10 decks)

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