Chapter 26- Aldehydes and Ketones

Question 1

What are aldehydes?

Answer 1

Organic compounds with the -CHO functional group containing a carbonyl group C=O at the end of the molecule

Question 2

How are aldehydes produced?

Answer 2

Produced from initial oxidation and distillation of primary alcohols

Question 3

How are aldehydes oxidised?

Answer 3

Aldehydes are readily oxidised in the presence of acidified potassium dichromate to produce a carboxylic acid

Question 4

What are two chemical tests to distinguish between aldehydes and ketones?

Answer 4

Tollen’s test: produces a silver mirror
Fehling’s test: goes from blue solution to red precipitate
Ketones don’t react with either of these reagents

Question 5

What are ketones?

Answer 5

An organic molecule with the functional group C=O in the middle of the molecule

Question 6

How are ketones produced?

Answer 6

Produced from oxidation of secondary alcohols with acidified potassium dichromate

Question 7

How are ketones oxidised?

Answer 7

Cannot be oxidised further

Question 8

What is a carbonyl group?

Answer 8

A functional group with a C=O double bond

Question 9

What happens when aldehydes and ketones are reduced?

Answer 9

Aldehydes produce primary alcohols when reduced
Ketones produce secondary alcohols when reduced

Question 10

What reducing agent is used to reduce aldehydes and ketones?

Answer 10

Sodium borohydride NaBH4 is used as a reducing agent.

Question 11

What is the nucleophile used when reducing aldehydes and ketones?

Answer 11

:H- ion is the nucleophile, provided by NaBH4.

Question 12

What is a necessary condition for the reduction of aldehydes and ketones?

Answer 12

Aqueous conditions as an H+ ion from the water molecule is needed

Question 13

What is a nucleophile?

Answer 13

An electron pair donor

Question 14

How are hydroxy-nitriles produced?

Answer 14

Nucleophilic addition reactions with a -:CN nucleophile, followed by reaction with a dilute acid. This is a form of synthesis as it increases the length of the carbon chain by one.

Question 15

What is the nucleophile used when producing hydroxy-nitriles?

Answer 15

-:CN nucleophile, provided by KCN most often

Question 16

What is the reaction mechanism for producing a hydroxy-nitrile from an aldehyde or ketone?

Answer 16

Lone pair from -:CN nucleophile goes to positive nucleus and one pair of electrons from C=O goes to O making it negative. Lone pair on O now goes to H+ ion from dilute acid to form OH group

Question 17

How are enantiomers produced from the nucleophilic addition from -:CN nucleophiles?

Answer 17

The -:CN nucleophile can attack the C nucleus in the planar carbonyl from above or below and the C atom attacked is often a chiral centre, producing two enantiomers

Question 18

How do you name hydroxy-nitriles?

Answer 18

C bonded to N is carbon atom one and is part of the carbon chain

Question 19

What are the dangers of KCN?

Answer 19

Dangerous if ingested or inhaled
Reacts with moisture to produce HCN, a toxic gas

Question 20

Why is KCN used as the reagent instead of HCN for production of hydroxy-nitriles?

Answer 20

HCN is hard to store as a gas, is toxic and reacts to form dangerous byproducts