Carbonyl Compounds Flashcards
Hydroxynitrile from a carbonyl and reaction type
Reagents : KCN in dilute acid (H2SO4)
Nucleophilic substitution
What is the geometry of carbonyls?
- trigonal planar, with the centre being the carbon atom bonded to the oxygen
Why do carbonyl reactions (that produce products with a chiral carbon centre) produce racemic mixtures?
-given carbonyls have a trigonal planar shape
-nucleophiles can attack from above or below the plane of the ring
-producing both possible enantiomers
Why is dangerous to use HCN to create a hydroxynitrile?
-HCN is dangerous gas, if inhaled it can kill you (plus it doesn’t dissociate readily)
What is the reducing agent used to reduce carbonyls
[H] = LiAlH4 (lithium aluminium hydride)
Hydroxycarboxylic acid from a hydroxynitrile
Acid hydrolysis
- heat under reflux with a dilute aqueous acid e.g HCl (aq)
Reduction of an aldehyde —> reagents, conditions and product
Reagents : LiAlH4 in DRY ETHER!
Product : PRIMARY alcohol
Why must LiAlH4 be used in dry ether
The reaction between LiAlH4 and water is extremely exothermic - it releases lots of energy
Reduction of a ketone : reagents,conditions and product
Reagents : LiAlH4
Conditions : dry ether
Product : SECONDARY alcohol
What forms the basis of the tollens reagent and Fehlings test for aldehydes?
- the fact that aldehydes can be further oxidised
-whilst the aldehydes are oxidised the species in the test solution are reduced —> often giving a colour change
Why do tollens and Fehlings only work in aldehydes?
-Only aldehydes can be further oxidised
-ketones and carboxylic acids can not
Explain the chemistry behind the Fehlings/ Benedict’s test
- Blue solution of Cu2+
- Redox reaction occurs in which aldehydes are oxidised, and Cu2+ reduced to Cu+
-Cu+ forms a red precipitate
Explain the chemistry behind the tollens reagent (silver nitrate solution) test
- Tollens contains [Ag(NH3)]+
- when the aldehyde is oxidised, the Ag+ in the complex is reduced to give Ag(s)
-Hence giving the silver mirror
