26.2- REACTIONS OF THE CARBONYL GROUP IN ALDEHYDES AND KETONES Flashcards
(27 cards)
What type of reactions are many of the reactions of carbonyl compounds?
nucleophilic addition reactions
What other reactions do carbonyl compounds undergo other than nucleophilic addition reactions?
redox reactions
What is produced when a carbonyl compound reacts with sodium/potassium cyanide + HCl?
hydroxynitriles
Why are hydroxynitriles useful in synthesis
as both -OH and -CN groups reactive + can be converted into other functional groups
When is a racemic mixture of two optical isomers (enantiomers) produced? (addition of hydrogen cyanide)
when carried out with an aldehyde or unsymmetrical ketone
Why is a racemic mixture produced of two optical isomers (enantiomers) produced when carried out with an aldehyde or an unsymmetrical ketone?
as :CN- ion may attack from above or below the flat C=O group
What can aldehydes be oxidised into?
carboxylic acids
What is used to represent the oxidising agent?
[O]
What is a commonly used oxidising agent?
acidified (with sulphuric acid) potassium dichromate
Can ketones be oxidised easily into carboxylic acids?
no
Why can’t ketones be oxidised easily into carboxylic acids?
as, unlike aldehydes, a C-C bond must be broken
What do stronger oxidising agents do to ketones? (oxidation)
stronger oxidising agents break hydrocarbon chain of ketone molecule resulting in shorter chain molecule, CO2 + water
What is the basis of distinguishing between aldehydes and ketones?
weak oxidising agents can oxidise aldehydes but not ketones
What is Fehling’s solution made up from?
mixture of two solution
What two mixtures of solution is Fehling’s mixture made up of?
Fehling’s A which contains Cu2+ ion and so is coloured blue, and Fehling’s B which contains an alkali + complexing agent
What happens when an aldehyde is warmed with Fehling’s solution?
brick red precipitate of copper (I) oxide produced as copper (II) oxidises aldehyde to carboxylic acid, and is itself reduced to copper (I)
What happens when a ketone is warmed with Fehling’s solution?
no reaction
What does Tollen’s reagent contain?
complex ion [Ag(NH3)2]+ which is formed when aqueous ammonia added to aqueous solution of silver nitrate
What happens when an aldehyde is warmed with Tollen’s reagent?
metallic silver formed
aldehydes oxidised to carboxylic acids by Tollen’s reagent
Ag+ reduced to metallic silver
silver mirror will be formed on inside of test tube
Equations for aldehyde being oxidised and silver being reduced with silver mirror test?
RCHO + [O] -> RCOOH
[Ag(NH3)2] + E- -> Ag + 2NH3
What happens when a ketones is warmed with Tollen’s reagent?
no reaction to test
Example of reducing agent that will reduce both aldehydes and ketones to alcohols?
sodium tetrahydridoborate (III) in aqueous solution
When the reducing agent sodium tetrahydridoborate (III) acts on an aldehyde or ketone, what does this generate?
nucleophile :H-, hydride ion
What does the nucleophile :H- do?
reduces partially positive C𝛿+ = O𝛿- but not C=C as it’s repelled by high electron density in C-C bond, but attracted to C𝛿+ of C=O bond
