carbonyls Flashcards
give examples of a carbonyl
aldehyde and ketone
The ____ carbonyls are ____ in water because they can form ____ bonds with water.
smaller, soluble , hydrogen
Aldehydes can be oxidised to _____, but ketones cannot be oxidised.
carboxylic acids
The C=O bond is polarised because O is more electronegative than carbon. The positive carbon atom
attracts ____.
nucleophiles
In comparison to the C=C bond in alkenes, the C=O is ____ and does not undergo addition reactions easily.
stronger
describe the oxidation of aldehydes
aldehyde –> carboxylic acid
Reagent: potassium dichromate (VI) solution and dilute sulfuric acid.
Conditions: heat under reflux
Observation: the orange dichromate ion (Cr2O7 2-) reduces to the green Cr 3+ ion
what else can aldehydes be oxidised by?
Tollens’ Reagent
Reagent: Tollens’ reagent formed by mixing aqueous ammonia and silver nitrate. The active substance is the complex ion of [Ag(NH3)2]+.
Conditions: heat gently
Reaction: aldehydes only are oxidised by Tollens’ reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms
Observation: with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no change.
CH3CHO + 2Ag+ + H2O –> CH3COOH + 2Ag + 2H+
describe the reduction of carbonyls
Reagents: NaBH4 In aqueous ethanol
Conditions: Room temperature and pressure
what are aldehydes reduced to
what are ketones reduced to
draw the nucleophillic addition mechanism
describe catalytic hyrdorgenation of carbonyls
Reagent: hydrogen and nickel catalyst
Conditions: high pressure
Example Equations
CH3CHO + H2 –> CH3CH2OH
CH3COCH3 + H2 –> CH3CH(OH)CH3
describe the Addition of hydrogen cyanide to carbonyls to form hydroxynitriles
Reaction: carbonyl –> hydroxynitrile
Reagent: sodium cyanide (NaCN) and dilute sulfuric acid.
Conditions: Room temperature and pressure
Mechanism: nucleophilic addition
draw the mechanism of addition of hydrogen cyanide
how can you use 2,5-DNP to test for a carbonyl group
forms orange precipitate
Then to differentiate an aldehyde from a ketone use Tollen’s reagent.
describe the use of Tollen’s reagent
Reagent: Tollens’ reagent formed by mixing aqueous ammonia and silver nitrate. The active substance is the complex ion of [Ag(NH3)2]+
Conditions: heat gently
Reaction: aldehydes only are oxidised by Tollens’ reagent into a carboxylic acid. The silver(I) ions are reduced to silver atoms
Observation: with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no change.
