Topic 17.2 Carbonyl compounds Flashcards
Carbonyl group
The carbonyl group is a carbon atom joined by a double bond to an oxygen atom
-C=O
Carbonyl compounds can be classed as either aldehydes or ketones
Aldehydes
-Carbonyl compounds is where a hydrogen atom is bonded to the carbonyl group
-General formula: RCHO
- =O at the end of carbon chain
(Aledehydes are oxidised further to produce carboxylic acids …..
Ketone
Carbonyl compounds where there are only one hydrocarbon groups joined to the carbonyl group.
Bonding in carbonyl compounds
-Contain -C=O group
-Polar bond
-Electron density is greater near the δ- O atom
Physical properties in carbonyl compounds
-Distinctive smells
-Boiling temperature are between those of alkanes (low) and alcohol (high)
-Boiling points increase with chain length
-No hydrogen bonding but permanent dipole dipole attraction
Physical properties in ketones and aldehydes
-Smaller aldehydes and ketones are soluble in water - they can form hydrogen bonds with water
-Solubility decreases as chain length increases - hydrocarbon part of the molecules become more significant
Primary alcohol
Oxidised:
Primary alcohol —> aldehyde —>
carboxylic acid
Secondary alcohol
Oxidised:
Secondary alcohol —> ketone —> X
Tertiary alcohol
Tertiary alcohol —> X
Reagent observations: Felling’s reagent
Aldehyde: brick red, precipitate solid
Ketone: stays blue, no visible change
Reagent observations: Tollen’s reagent
Aldehyde: silver mirror, black precipitate
Ketone: stays colourless, no visible change
Reagent observations: sodium dichromate
Aldehydes: decolourises
Ketones: stays purple, no visible change
Reagent observations: K2Cr2O7
Aldehyde: colour change, orange to green
Ketone: stays orange, no visible change
Reaction with proponal/anone: Sodium dicromate
Propanal: green
Propanone: orange (no change)
Reaction with proponal/anone: Felling’s solution
Propanal: light blue
Propanone: dark blue