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Chemistry Module 6 > 6.1.1 Aromatic Compounds > Flashcards

6.1.1 Aromatic Compounds Flashcards

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1
Q

Aliphatic

A

Straight or branched chain organic substancex

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2
Q

Aromatic/arene

A

Includes one of more rings of six carbons with delocalised bonding

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3
Q

Benzene structure

A

C6H6
Carbon to 2 carbons and one hydrogen by single covalent sigma bonds
One unused electron in each C atom in a p orbital, perpendicular to plane of ring
6 p electrons are delocalised into a ring above and below carbon atoms

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4
Q

Kekule model

A

Alternate single and double covalent bonds

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5
Q

What type of molecule is benzene what does this suggest

A

Planar

All C-C bonds are the same and have a length and bond energy between a CC single and CC double

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6
Q

HCC bond angle in benzene

A

120 degrees

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7
Q

What is delocalisation energy

A

Increase in stability connected to delocalisation

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8
Q

Enthalpies of hydrogenation

A

Would expect when 3 double bonds for the hydrogenation to be 3 times greater
Real amount is less as 6 pi electrons are delocalised
Delocalised is more thermodynamically stable

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9
Q

Evidence for why benzene has a delocalised structure

A

Bond length intermediate between short C=C and long C-C
🔼H hydrogenation less exothermic than expected when compared to that of Kekule structure
Only reacts with Br2 at high temp or presence of halogen carrier
Doesn’t undergo addition reactions

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10
Q

Reactions of benzene

A

Doesn’t undergo addition reactions as they’d have to break delocalised system
Electrophillic substitution

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11
Q

Toxicity of benzene

A

Benzene is a carcinogen
Methylbenzene less toxic and reacts more readily as methyl side group releases electrons into delocalised ring, more attractive to electrophiles

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12
Q

Nitration of benzene

A 
Benzene to nitrobenzene 
Conc nitric scid 
Conc sulfuric acid catalyst 
Electrophillic substitution 
Uses NO2+ as electrophile
50 degrees temp
Reacts slowly
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13
Q

Bonding in delocalised

A

Draw hexagon with p orbitals above and below
Show overlap
Then draw ring

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14
Q

Enthalpy of hydrogenation

A

Enthalpy change when one mole of unsaturated compound reacts with an excess of hydrogen to become fully saturated

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15
Q

Nitration full stages

A 
1. Create electrophile: 
HNO3 + H2SO4 -> NO2+ +H2SO4- +H2O
2. Dative covalent bond (mechanism)
3. Catalyst regenerated:
H+ + HSO4- -> H2SO4
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16
Q

Halogenation

A 
Benzene to bromobenzene 
Bromine
Iron 3 bromide catalyst (FeBr3)
Electrophillic substitution 
Can be done with chlorine with (AlCl3 or FeCl3)
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17
Q

naming aromatic compounds

A

if group is: alkyl, halogen, nitro then added as a prefix ___ benzene
if group is: amine,ester, alcohol or ketone then phenyl___

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18
Q

which groups get ___benzene

A

alkyl
halogen
nitro

19
Q

which groups get phenyl ___

A

amine
ester
alcohol
ketone

20
Q

Halogenation full stages

A 
1. Create electrophile:
AlBr3 + Br2 -> AlBr4- + Br+
2. Dative covalent bond forms unstable intermediate
3. Catalyst regenerated:
H+ + AlBr4- -> AlBr3 + HBr
21
Q

which category of reactions are alkylation and acylation?

A

Friedel Crafts

22
Q

Alkylation

A

benzene to alkyl benzene
chloroalkane in the presence of anhydrous aluminium chloride catalyst
heat under reflux
electrophillic substitution

23
Q

Alkylation full steps

A 
1. Create electrophile:
AlCl3 + CH3Cl -> AlCl4- + CH3+
2. Accepts lone pair, dative covalent bond is formed 
3. Catalyst is regenerated
AlCl4- + H+ -> AlCl3 + HCl
24
Q

Acylation

A

benzene to phenyl ketone
acyl chloride in the presence of anhydrous aluminium chloride catalyst
heat under reflux at 50 degrees
electrophilic substitution

25
Q

Acylation full steps

A 
1. Create electrophile
AlCl3 + CH3COCl -> AlCl4- + CH3CO+
2. Forms a dative covalent bond
3. Catalyst regeneration: 
AlCl4- + H+ -> AlCl3 + HCl
26
Q

naming acyl chlorides

A

look like a carboxylic acid but have Cl in replacement of OH
Name carbon chain first (ethanoyl) then place “chloride” on the end

27
Q

phenol definition

A

aromatic compound where a hydroxyl (OH) group is directly bonded to the benzene ring

28
Q

phenols as acids

A

very weakly acidic

weaker than carboxylic acids

29
Q

reactions: phenols vs carboxylic acids

A

both: react with sodium metal and sodium hydroxide (metals and strong bases)
carboxylic acids: react with sodium carbonate (weak base)
phenols: bromine

30
Q

phenols in water, proof of weak acid

A

less soluble in water than alcohols due to non-polar benzene ring
dissolved in water partially dissociates to form phenoxide ion and a proton
as it only partially dissociates phenol is a weak acid

31
Q

phenols reaction with alkalis

A

forms a salt (sodium phenoxide) and water in neutralisation reactions
acid + alkali -> salt + water
C6H5OH + NaOH -> C6H5 O- Na+ + H2O
if more than one OH then excess alkali, put alkali on each

make sure ions aren’t bonded but just next to each other

32
Q

phenols reactions with metals

A

need to balance this equation
acid + metal -> salt + hydrogen
phenol + sodium -> sodium phenoxide + hydrogen

33
Q

bromination with phenol

A

Br2
room temperature
decolourised water forms a white ppt

34
Q

bromination with phenol full steps

A

max 3 bromine added

decolarised water forms a white ppt

35
Q

why is phenol more reactive with bromine than benzene

A

one of the lone pairs of electrons on p orbital of oxygen atom in OH is partially delocalised into the ring
increases the electron density
electrophile is more polarised
so can react more readily

36
Q

nitration with phenol

A

reacts with dilute nitric acid
at room temperature
adds to carbon 2,4 or 6

37
Q

nitration of phenol full steps

A

react with dilute nitric acid
forms 2-nitrophenol or 4-nitrophenol
2 nitro is more common as 6 would be the same as 2 is the second carbon was free
also forms water

38
Q

effect of electron donating

A

increases electron density

39
Q

effect of electron withdrawing

A

decreases electron density

40
Q

electron donating

A

side chains increase the density
allow electrophiles to react faster, activating groups
in OH and NH2 the O and the N lone pairs overlap the ring
substitute onto position 2,4,6
2,4 directing

41
Q

electron withdrawing

A

side chains decrease density
slow electrophile reactions, de-activating groups
NO2, the O is more electronegative so electrons are drawn away from the ring
groups direct substitution to 3 and 5
3-directing

42
Q

2,4-directing

A

OH
NH2
F, Cl, Br
R (carbon chain)

43
Q

3-directing

A

NO2
COOH
CHO
COOR (ester)

Chemistry Module 6 (10 decks)

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