Organic synthesis and analysis

Question 1

What is important to remember in organic synthesis

Answer 1

To keep the number of steps as small as possible to maximise the yield of the target molecule.

Question 2

What is the oxidising agent we use for most reactions (A-level)

Answer 2

Acidified potassium dichromate

Question 3

List the various reducing agents and which reactions they are used in

Answer 3

1) NaBH4: Will reduce polar unsaturated groups such as C=O but not non-polar unsaturated groups such as C=C. This is because it generates the nucleophile :H- (hybrids ion) which attacks C+ but is repelled by C=C.
2) Hydrogen with a nickel catalyst H2/Ni which reduces the C=C bond but not C=O
3) Tin and hydrochloric acid Sn/H+ which reduces R-NO2 and R-NH2

Question 4

How can alcohols be dehydrated

Answer 4

Alcohols can be converted to alkenes by passing their vapours over heated aluminium oxide or by acid catalysed elimination reactions.

Question 5

How do you test for an alkene and what is the result

Answer 5

• shake with bromine water
• the original red-brown colour of the bromine water disappears.

Question 6

How do you test for a halogenoalkane and what is the result

Answer 6

1) add NaOH and warm
2) acidify with HNO3
3) add AgNO3
- a precipitate of the silver halide forms

Question 7

How do you test for an alcohol and what is the result

Answer 7

• add acidified K2Cr207
• orange colour turns green (primary,secondary alcohols and aldehydes)

Question 8

How do you test for an acid

Answer 8

• Add NaHCO3
• bubbles observed as CO2 given is