Carbonyl Compounds Flashcards
Describe their solubility in water.
Smaller carbonyls are soluble in water as they can form hydrogen bonds with water.
Pure carbonyls can’t hydrogen bond, but instead bond by permanent dipole.
Describe the oxidation of alcohols.
Potassium dichromate: K2Cr2O7 & H2SO4.
1• alcohols: [O] to aldehydes (distil)
2[O] to carboxylic acids (reflux)
2• alcohols: [O] to ketones.
Observation: colour change : Orange–> green. The orange dichromate ion(Cr2O7^2-) is reduced to the green Cr^3+ ion.
Describe the reduction of carbonyl compounds.
What is the mechanism?
Aldehydes 2[H] to 1• alcohols.
Ketones 2[H] to 2• alcohols.
Reducing agents: NaBH4 or LiAl4. They contain nucleophilic hydride ions that are attracted to the +ve carbon of the C=O.
Mechanism: Nucleophilic Addition Reaction.
What is Tollen’s reagent?
It’s formed when aqueous ammonia mixes with silver nitrate –> complex ion: [Ag(NH3)2]^+.
Used to distinguish between ketones and aldehydes. Only aldehydes react with TR to form an a silver mirror.
The aldehyde is oxidised to the carboxylic acid and the silver ion is reduced to the silver metal. Ag^+ +e- —> Ag(s).
What is Brady’s reagent?
2,4-DNPH. It forms an orange precipitate when a carbonyl group is present.
The melting point of the crystal formed can be used to determine what carbonyl was used, by comparing it to a database of known carbonyl melting points.
What are carbonyls?
Carbonyls are compounds that contain the C=O bond.
It can either be ketones or aldehydes.
