organic synthesis [O2] PAPER 2

Question 1

Suggest why chemists usually aim to design production methods with fewer steps.

Answer 1

• less energy used
• better yield

Question 2

Suggest why chemists usually aim to design production methods with a higher atom economy.

Answer 2

• less waste
• less pollution

Question 3

[X=halogen]

reaction between a haloalkane and NaOH to form an alcohol and NaX

1. conditions?
2. mechanism?
3. what is the role of NaOH?

Answer 3

1. warm, aqueous
2. nucleophilic substitution
3. nucleophile

Question 4

[X=halogen]

reaction between a haloalkane and KCN to form a cyanide and KX

1. conditions?
2. mechanism?
3. what is the role of CN?

Answer 4

1. warm, ethanolic, aqueous
2. nucleophilic substitution
3. nucleophile

Question 5

[X=halogen]

reaction between a haloalkane and ammonia to form an amine

1. conditions?
2. mechanism?
3. what is the role of NH3?

Answer 5

1. excess concentrated ethanolic NH3
2. nucleophilic substitution
3. nucleophile (and base for the second step?)

Question 6

[X=halogen]

reaction between a haloalkane and KOH to form an alkene, water and KX

1. conditions?
2. mechanism?
3. role of OH ions?

Answer 6

1. hot, ethanolic
2. elimination
3. base

Question 7

what are the three steps of free-radical substitution?

Answer 7

1. initiation
   (molecule -> radical + radical)
2. propagation
   (molecule + radical -> radical + molecule)
3. termination
   (radical + radical -> molecule)

Question 8

what conditions are required for free-radical substitution and why?

Answer 8

• UV light
• break (C-X, C-H) bonds

[X=halogen]

Question 9

name and outline the mechanism to form a halogenoalkane from an alkene and Br2 / HBr

Answer 9

• electrophilic addition
• Br2 / HBr = electrophile
(mechanism is the same for Br2 - just Br instead of H)

Question 10

name and outline the mechanism for the reaction between an alkene and sulfuric acid, and state conditions required

Answer 10

• electrophilic addition
• conditions: concentrated H2SO4, cold (typically room temp.)

Question 11

outline the reaction and conditions to form an aldehyde from the oxidation of an alcohol, and the further oxidation of the aldehyde to form a carboxylic acid

Answer 11

• 1° alcohol + [O] -> aldehyde + water
• aldehyde + [O] -> carboxylic acid + water
• warmed with acidified potassium dichromate (VI)
• distilled [aldehyde is distilled off - if this isn’t done, it would oxidise to form the carboxylic acid]

e.g. ethanol:

Question 12

outline the reaction, conditions and reagent used to form a carboxylic acid from the oxidation of an alcohol

Answer 12

• 1° alcohol + 2[O] -> carboxylic acid + water
• conditions: under reflux
• reagent: acidified potassium dichromate (VI)
e.g.

Question 13

outline the reaction and conditions for the formation of a ketone from an alcohol

Answer 13

• 2° alcohol + [O] -> ketone + water
• acidified potassium dichromate (VI)
• reflux
e.g.

Question 14

Reagent, conditions and mechanism for the dehydration of an alcohol to form an alkene?

Answer 14

• conc. sulfuric/phosphoric acid
• hot
• elimination

a mixture of alkenes can be formed depending on the alcohol (different carbocations)

Question 15

name the reaction, conditions and outline the mechanism to form an alcohol from an alkene

Answer 15

• electrophilic addition (hydration too)
• alkene + steam -> alcohol
• conc. H2SO4 catalyst
• this is how ethanol from ethene can be obtained

Question 16

name and outline the mechanism, state the reagent, and the conditions for the reduction of aldehydes to primary alcohols / ketones to secondary alcohols.

Answer 16

• nucleophilic addition
• NaBH4
• aqueous

Question 17

name and outline the mechanism, state the reagents, and the conditions for the reaction of carbonyl compounds to produce a hydroxynitrile.

Answer 17

• nucleophilic addition
• KCN and dilute acid
• aqueous

Question 18

esterification/ester hydrolysis reaction and conditions?

Answer 18

• alcohol + carboxylic acid ⇌ ester + water
• above the other way round = ester hydrolysis (in acidic conditions)
• concentrated strong acid catalyst, e.g. H2SO4

e.g.

Question 19

saponification reaction?

Answer 19

• ester + alkali → salt of carboxylic acid + alcohol
• this is ester hydrolysis in alkaline conditions

Question 20

saponification of a lipid?

Answer 20

lipid + 3KOH → 3 salts of fatty acids + glycerol

Question 21

name and outline the mechanism for the acylation of R—OH using R—COCl.

Answer 21

nucleophilic addition-elimination

Question 22

name and outline the mechanism for the acylation of R—NH2 using R—COCl.

Answer 22

nucleophilic addition-elimination

Question 23

name and outline the mechanism, and state the reagents and conditions, for the nitrification of benzene.

Answer 23

• electrophilic substitution
• conc. HNO3
• conc. H2SO4
• 50°C

Question 24

name and outline the mechanism, and state the reagents and conditions, for the Friedel-Crafts acylation of benzene.

Answer 24

• electrophilic substitution
• acyl chloride/acid anhydride
• AlCl3 catalyst
• anyhydrous

Question 25

generation of electrophile for the nitration of benzene?

Answer 25