Organic Synthesis (Chapter 16.2, Chapter 28.1, 28.3)

Question 1

What are the two steps for the synthesis of an organic molecule with several functional group?

Answer 1

1) draw out the structure of molecule and identify all the functional groups
2) predict the properties and reactions of the molecule by examining the functional groups

Question 2

What is a target molecule?

Answer 2

The compound that the chemist is attempting to prepare by organic synthesis

Question 3

What are the three steps in a two stage synthesis to covert a starting molecule into the target molecule?

Answer 3

1) identify the functional groups in the starting and target molecules
2) identify the intermediate that links the starting and target molecules
3) state the reagents and conditions for each step

Question 4

Why do reactions that form C-C bonds have a central importance to organic chemistry?

Answer 4

They allow the synthesis of new compounds containing more carbon atoms

Question 5

What are three ways that C-C bonds can be formed?

Answer 5

1) by lengthening a carbon chain
2) adding a side chain to benzene ring
3) introducing new functional groups which can then be reacted further

Question 6

What are the two ways that nitriles (-CN) can be formed?

Answer 6

1) from haloalkanes and KCN/NaCN

2) from aldehydes/ketones and HCN (NaCN and H2SO4)

Question 7

Describe the formation of nitriles from haloalkanes

Answer 7

• Nitriles can be formed by reacting haloalkanes with sodium or potassium cyanide in ethanol via a nucleophilic substitution mechanism, increasing the length of the carbon chain
• e.g. chloropropane + KCN => propanenitrile + KCl

Question 8

Describe the formation of hydroxynitriles from aldehydes/ketones

Answer 8

• Aldehydes and ketones react with HCN in nucleophilic addition reaction, forming a C-C bond ∴ increasing the number of carbon atoms in the molecule
• HCN is too poisonous to use and an increased reaction rate can be obtained in the presence of CN- ∴ a mixture of NaCN and H2SO4 is used to improve safety and increase reaction rate
• e.g. CH3COCH3 + HCN => CH3C(OH)(CN)CH3
• or CH3COCH3 + KCN + H2O + H2SO4 => CH3C(OH)(CN)CH3 + KOH

Question 9

When are nitriles useful intermediates?

Answer 9

In the synthesis of other organic compounds e.g. amines and carboxylic acids

Question 10

What can nitriles be reduced to?

Answer 10

Amines

Question 11

Describe the reduction of nitriles to amines

Answer 11

• Nitriles can be reduced to amines by reacting with hydrogen in the presence of a nickel catalyst
• e.g. CH3CH2CN + 2H2 => CH3CH2CH2NH2

Question 12

Describe the hydrolysis of nitriles

Answer 12

• Nitriles undergo hydrolysis to form carboxylic acids by heating with dilute aqueous acid e.g. HCl
• e.g. CH3CN + 2H2O + HCl => CH3COOH + NH4Cl

Question 13

What two reactions form carbon-carbon bonds to benzene rings?

Answer 13

1) acylation

2) alkylation

Question 14

What kind of reaction mechanisms does acylation and alkylation take place by?

Answer 14

Electrophilic substitution

Question 15

What is alkylation?

Answer 15

• A reaction that transfers an alkyl group from a haloalkane to a benzene ring in the presence of a Friedal-Crafts catalyst (halogen carrier)
• e.g. benzene + chloroethane => ethylbenzene + HCl

Question 16

What is acylation?

Answer 16

• Formation of a ketone when benzene reacts with an acyl chloride in the presence of AlCl3 catalyst
• e.g. benzene + ethyl chloride => phenyl chloride + HCl