Aromatic and Carbonyls

Question 1

Kekule (1)

Answer 1

Benzene does not undergo electrophilic substitution with Bromine

Question 2

Kekule (2)

Answer 2

Expected isomers do not exist

Question 3

Kekule (3)

Answer 3

Enthalpy change of hydrogentation of benzene is lower than expected

Question 4

Kekule (4)

Answer 4

All carbon bond lengths are equal whioch shows that alternating C=C bonds are not present. C-C are longer than C=C bonds.

Question 5

Kekule (5)

Answer 5

Electron density is even distributed throughout the benzene moleule

Question 6

Nitration

Answer 6

1. HSO4 + HNO3 -> NO2+ + HSO4- + H2O
   Conditions at 50C
2. HSO4 + H+ -> H2SO4

Question 7

Halogenation

Answer 7

1. FeX3 + X2 -> FeX4- + X+
2. FeX4- + H+ -> FeX3 + HX

Question 8

Acylation

Answer 8

1. Benzene + acyl chloride
   AlCl3 catalyst
2. Aroamtic ketone forms

Question 9

Alkylation/Friedel-Crafts reaction

Answer 9

Swapping a H with an alkyl chain
1. Benzen + haloalkane
Catalyst AlCl3

Question 10

Phenol (reactions)

Answer 10

Alcohols do not react with bases
Phenol reacts with bases but not carbonates
Carboxylic acids react with weak bases

Question 11

Phenol (1)

Answer 11

Phenol + base -><- metal phenoxide + water

Question 12

Phenol (2)

Answer 12

Phenol -> 2/4 nitro-phenol
Conditions - RTP and HNO3

Question 13

Phenol (3)

Answer 13

Phenol + 3X2 -> 2,4,6- trihalide phenol + 3HX
Conditions - RTP
Forms a white precipitate

Question 14

Testing for a carbonyl bond

Answer 14

1. 2,4 - DNPH (brady’s reagent) is mixed with an unknown organic solution
2. If an orange precipitate forms then the solution either contains aldehydes or ketones
3. The orange precipitate is filtered using a bucher funnel under pressure and is dissolved in teh smallest amount of hot solvent to form crystals (recrystallisation)
4. The melting point of is found by using a melting block (not quite reliable as internal temperature is hotter than the surface temperature)
5. With the results calculated a table of melting points is used to deduce exactly what ketone/aldehyde it is.

Question 15

Testing for aldehydes

Answer 15

1. Tollens reagent (ammoniacal silver nitrate) reacts with aldehydes but not ketones
2. This is due to ketones not being abe to be oxidised
3. Aldehydes can be oxidised and silver ions are reduced
4. Forms a grey precipitate

Question 16

Aldehydes (1)

Answer 16

Reduction with NaBrH4
Aldehyde -> Alcohol (primary)

Question 17

Aldehydes (2)

Answer 17

Reduction with HCN
Aldehyde -> hydroxynitrile

Question 18

Ketone (1)

Answer 18

Reduction with NaBrH4
Ketone -> Alcohol (secondary)

Question 19

Ketone (2)

Answer 19

Reduction with HCN
Ketone -> Hydroxynitrile

Question 20

Carboxylic acid (1)

Answer 20

Carboxylic acid + metal -> metal carboxylate acid + H2

Question 21

Carboxylic acid (2)

Answer 21

Carboxylic acid + carbonates -> metal carboxylate acid + water + carbon dioxide

Question 22

Carboxylic acid (3)

Answer 22

Carboxylic acid + metal oxide -> metal carboxylate acid + water

Question 23

Carboxylic acid (4)

Answer 23

Carboxylic acid + alkali -> metal carboxylate acid

Question 24

Carboxylic acid (5)

Answer 24

Carboxylic acid + alcohol (primary) -> ester + water
Ester name = alcohol (yl) carboxylic acid (oate)

Question 25

Esters (1)

Answer 25

Ester + H2O -><- Carboxylic acid + primary alcohol
-> Hydrolysis and hot aqueous acid (catalyst)
<- Esterification and H2SO4 (catalyst)

Question 26

Esters (2)

Answer 26

Ester + alkali -> metal carboxylate + alcohol
Reflux