17.2.3 - Nucleophilic addition reactions

Question 1

What is the name of the reaction when hydrogen cyanide reacts with aldehydes and ketones?

Answer 1

Nucleophilic addition

Question 2

How many steps are there in the reaction between hydrogen cyanide and a carbonyl compound?

Answer 2

2 steps

Question 3

What happens in the first step in the reaction between hydrogen cyanide and a carbonyl compound?

Answer 3

The cyanide ion attacks the carbon atom of the carbonyl compound.
This forms an intermediate containing an oxygen atom with a lone pair and a negative charge.

Question 4

What happens in the second step in the reaction between hydrogen cyanide and a carbonyl compound?

Answer 4

A hydrogen cyanide ion reacts with the intermediate.
A cyanide ion is formed.
A CN and OH group are attached to the carbon.

Question 5

Why does the product of the reaction between a carbonyl compound and hydrogen cyanide have no optical activity?

Answer 5

The arrangement of atoms joined to the C=O bond is planar.
So there is an equal chance of the cyanide ion attacking from each side of the plane.
Equal amounts of enantiomers formed

Question 6

What is Brady’s agent also known as?

Answer 6

2,4 - dinitrophenylhydrazine
(2,4 DNPH)

Question 7

What is formed when Brady’s agent reacts with a carbonyl compound?

Answer 7

A brightly coloured orange solid

Question 8

What do you need to do to 2,4 DNPH derivatives before we measure their melting points?

Answer 8

Filter
Purify
Dry

Question 9

How do you identify the carbonyl compound that reacts with 2,4 DNPH?

Answer 9

Compare the melting points of the derivatives with the values in a data book.