Organic II

Question 1

Write the overall equation of the reduction of butanone using [H] as the reductant

(1 mark)

Answer 1

CH3CH2COCH3 + 2[H] -> CH3CH3CH(OH)CH3

Question 2

By considering the formation of butan-2-ol from butanone, explain why it has no effect on plane-polarised light

(6 marks)

Answer 2

Formation:
- Nucleophilic addition
- Planar carbonyl group
- H- equally attacks from both sides

Nature of product:
- Butan-2-ol exists in 2 chiral forms
- Equal amounts of each enatomer formed- racemic mixture

Optical activity:
- Optical isomers rotate the plane of polarised light equally in both directions
- Racemic mixture so effects cancel

• Remember PEAR

Question 3

Name the mechanism of phenol to 4-nitrophenol

(1 mark)

Answer 3

Electrophilic substitution

Question 4

Give one reason why ethanoyl chloride is not used in industrial synthesis

(1 mark)

Answer 4

Forms strong acid (HCL) / corrosive

Question 5

Explain the bonding in and the shape of a benzene molecule.

Compare the stability with that of the hyporthetical cyclohexa-1,3,5-triene molcule.

Use the data in your answer:
Cyclohexene + H2 -> Cyclohexane : enthalpy = -120 kJmol-1
Benzene + 3H2 -> Cyclohexane : enthalpy = -208 kJmol-1

6 marks

Answer 5

Stage 1: Bonding
- Each C has 3 covalent bonds
- Spare electrons in a orbital overlap to form a Pi cloud
- Delocalisation can take place

Stage 2: Shape
- Planar
- Hexagon/ 6 carbon ring/ 120’ bond angle
- C-C bonds equal in length

Stage 3: Stability
- Expected enthalpy change of cyclohexatriene: -360
- Enthalpy change of hydrogenation of benzene is less exothermic by 152
- Benzene is more stable than cyclohexatriene

Question 6

Electrophilic substitution: Friedel-Crafts Acylation

Consider the reaction of benzene with CH3CH2COCl
- Write an equation for this reaction and name the organic product
- Identify the catalyst required in this reaction
- Write equations to show how the catalyst is used to form a reactive intermediate and how the catalyst is reformed at the end of the reaction

5 marks

Answer 6

• C6H6 + CH3CH2COCl -> C6H5COCH2CH3 +HCl
• Phenylpropanone
• AlCl3
• CH3CH2COCl + AlCl3 -> CH3CH2C+O + AlCl4-
• AlCl4- + H+ -> AlCl3 +HCl

Question 7

Electrophilic substitution: Nitration

• Give the reagents used to produce the electrophile in Nitration
• Write an equation showing the formation of this electrophile
• Write an equation for the overall reaction

Answer 7

• Conc HNO3 and Conc H2SO4
• H2SO4 + HNO3 -> HSO4- + +NO2 + H2O
• C6H6 + HNO3 -H2SO4-> C6H6NO2 + H2O

Question 8

When methylbenzene reacts with ethanoyl chloride and aluminium chloride, a similar substitution reaction occures but the reaction is faster than the reaction of benzene- suggest why

2 marks

Answer 8

• Methyl has positive inductive effect/ increases electron density on benzene ring
• Electrophile attracted more

Question 9

What is the general formula for an ester?

Answer 9

RCOOR’

Question 10

Give the word equation and skeletal equation of acid catalysed hydrolysis of propylethanoate.

Include the catalyst

Answer 10

Propylethanoate + H2O -> Ethanoic acid + Propan-1-ol

Make sure arrow is reversible ande H+ catalyst over the arrow

Question 11

Give the broken down word equation and skeletal equation of base catalysed hydrolysis of propylethanoate.

Include the catalyst

Answer 11

Propylethanoate + H2O -> Propan-1-ol + Ethanoic acid -> Sodium ethanoate + H2O

First arrow is reversible, catalyst on both arrows is NaOH

Question 12

Give the overall word equation and skeletal equation of base catalysed hydrolysis of propylethanoate.

Include the catalyst

Answer 12

Propylethanoate + NaOH-> Sodium ethanoate + Propan-1-ol

Regular arrow- H2O not needed since used and reproduced at the end

Question 13

Give the general formula for Acyl Chlorides

Answer 13

RCOCl

Question 14

Give the general formula for Acid Anhydrides

Answer 14

RCOOCOR’

Question 15

What is the definition of an optical isomer?

Answer 15

A non super-imposable mirror image

Question 16

State the hazard associated with the use of KCN

State a reason other than saftely why KCN is used instead of HCN

(2 marks)

Answer 16

• Toxic/ poinsonous
• HCN is too weak

Question 17

Name the mechanism for the reaction between potassium cyanide and ethanal

(1 mark)

Answer 17

Nucleophilic addiiton

Question 18

Give the IUPAC name of CH3CH2CH2CH2CH(OH)CN

(1 mark)

Answer 18

2-hydroxyhexanenitrile

Question 19

Explain how you would distiunguish between 2 seperate samples of stereoisomers

(2 marks)

Answer 19

• Plane polarised light
• Enantiomers would rotate in different directions

Question 20

Ethanol can be oxidised by acidified K2Cr2O7 to ethanoic acid in a two-step process.

In order to ensure that the oxidation to ethanoic acid is complete, the reaction is carried out under reflux.

Describe what happens when a reaction mixture is refluxed and explain why, in this reaction, it is necessary for complete oxidation to ethanoic acid

(3 marks)

Answer 20

• A mixture of liquids is heated to boiling for a prolonged time
• Vapour is formed which escapes the liquid mixture, is changed back to liquid and returned to liquid mixture
• Any ethanal and ethanol that initially evaporates can be oxidised

Question 21

Suggest 2 ways in which the melting point of crude aspirin differs from the melting point of pure aspirin

(2 marks)

Answer 21

• Value lower
• Range of values