Chapter 26 - Carbonyl Compounds

Question 1

What compounds have the carbonyl functional group

Answer 1

aldehydes and ketones

Question 2

aldehydes

Answer 2

have the carbonyl group on the end carbon, end in al

Question 3

ketones

Answer 3

have the carbonyl group on an inner carbon, end in one

Question 4

can carbonyl compounds be readily oxidised

Answer 4

• ketones are not readily oxidised
• aldehydes are oxidised to carboxylate;ic acids using an oxidising agent

Question 5

What is Tollens’ reagent used for

Answer 5

can be used to distinguish between aldehydes and ketones

Question 6

How is Tollens’ reagent made?

Answer 6

• pour silver nitrate solution into a testube (colourless)
• add few drops of NaOH until pale brown precipitate forms
• add few drops of dilute ammonia until precipitate dissolves

Question 7

How is Tollens’ reagent USED?

Answer 7

• Add aldehyde/ketone to the reagent and place in hot water bath (do not use bunsen flame as aldehydes and ketones are flammable
• Aldehydes reduce the [Ag(NH3)2] 2+ ions to silver which coats the inside of the flask

Question 8

What is Brady/s reagent/ 2,4-Dinitrophenylhydrazine used for

Answer 8

distinguish between aldehydes and ketones

Question 9

HOW does 2,4-DNP distinguish between aldehydes and ketones

Answer 9

• dissolved in concentrated sulphuric acid and methanol then added to the substance under test
• if a carbonyl group exists, a bright orange precipitate is formed
• only reacts with the C=O group in aldehydes and ketones, NOT in carboxylic acids

Question 10

How can a specific carbonyl compound be identified using 2,4-DNP

Answer 10

• the orange precipitate is a derivative of a carbonyl compound
• different carbonyl compounds produce different derivatives that all have different melting points
• can be identified against a library of known melting points

Question 11

What compound is formed when aldehydes and ketones are reduced

Answer 11

primary and secondary alcohols

Question 12

What is the reducing agent when reducing aldehydes and ketones

Answer 12

NaBH4 - sodium borohydride

Question 13

reduction of aldehyde equation

Answer 13

aldehydes are reduced to primary alcohols

Question 14

reduction of ketones equation

Answer 14

ketones are reduced to secondary alcohols

Question 15

mechanism for the reduction of aldehydes/ketones (same mechanism)

Answer 15

Nucleophilic addition

Question 16

Reaction of potassium cyanide and carbonyl compounds

Answer 16

• nucleophilic addition reaction
• forms hydroxynitrile (molecule contains OH and CN group)
• Potassium cyanide dissociates into its ions when dissolved in acidic solution
  -Hydrogen cyanide can also be used (no acid required)

Question 17

Mechanism of reaction between potassium cyanide and carbonyl compounds

Answer 17

Question 18

What happens if unsymmetrical ketone is used and reacted with potassium cyanide

Answer 18

mixture of enantiomers are produced

Question 19

risks using potassium cyanide

Answer 19

• irritant and very dangerous is ingested or inhaled (wear gloves, lab coat, goggles ect)
• forms toxic gas hydrogen cyanide when dissolved with moisture (use fume cupboard)