6.1.1 Aromatic Compounds

Question 1

Aliphatic

Answer 1

Straight or branched chain organic substancex

Question 2

Aromatic/arene

Answer 2

Includes one of more rings of six carbons with delocalised bonding

Question 3

Benzene structure

Answer 3

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

Question 4

Kekule model

Answer 4

Alternate single and double covalent bonds

Question 5

What type of molecule is benzene what does this suggest

Answer 5

Planar

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

Question 6

HCC bond angle in benzene

Answer 6

120 degrees

Question 7

What is delocalisation energy

Answer 7

Increase in stability connected to delocalisation

Question 8

Enthalpies of hydrogenation

Answer 8

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

Question 9

Evidence for why benzene has a delocalised structure

Answer 9

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

Question 10

Reactions of benzene

Answer 10

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

Question 11

Toxicity of benzene

Answer 11

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

Question 12

Nitration of benzene

Answer 12

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

Question 13

Bonding in delocalised

Answer 13

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

Question 14

Enthalpy of hydrogenation

Answer 14

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

Question 15

Nitration full stages

Answer 15

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

Question 16

Halogenation

Answer 16

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

Question 17

naming aromatic compounds

Answer 17

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

Question 18

which groups get ___benzene

Answer 18

alkyl
halogen
nitro

Question 19

which groups get phenyl ___

Answer 19

amine
ester
alcohol
ketone

Question 20

Halogenation full stages

Answer 20

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

Question 21

which category of reactions are alkylation and acylation?

Answer 21

Friedel Crafts

Question 22

Alkylation

Answer 22

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

Question 23

Alkylation full steps

Answer 23

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

Question 24

Acylation

Answer 24

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

Question 25

Acylation full steps

Answer 25

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

Question 26

naming acyl chlorides

Answer 26

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

Question 27

phenol definition

Answer 27

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

Question 28

phenols as acids

Answer 28

very weakly acidic | weaker than carboxylic acids

Question 29

reactions: phenols vs carboxylic acids

Answer 29

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

Question 30

phenols in water, proof of weak acid

Answer 30

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

Question 31

phenols reaction with alkalis

Answer 31

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

Question 32

phenols reactions with metals

Answer 32

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

Question 33

bromination with phenol

Answer 33

Br2 room temperature decolourised water forms a white ppt

Question 34

bromination with phenol full steps

Answer 34

max 3 bromine added | decolarised water forms a white ppt

Question 35

why is phenol more reactive with bromine than benzene

Answer 35

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

Question 36

nitration with phenol

Answer 36

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

Question 37

nitration of phenol full steps

Answer 37

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

Question 38

effect of electron donating

Answer 38

increases electron density

Question 39

effect of electron withdrawing

Answer 39

decreases electron density

Question 40

electron donating

Answer 40

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

Question 41

electron withdrawing

Answer 41

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

Question 42

2,4-directing

Answer 42

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

Question 43

3-directing

Answer 43

NO2 COOH CHO COOR (ester)