carbonyl compounds Flashcards
test for the carbonyl group
add 2,4-DNP solution
gives an orange/yellow/red precipitate
test for the aldehyde group
reaction with iodine in alkali
forms a yellow/cloudy precipitate
method to distinguish between keytone and aldehyde (using DNP)
1 add 2,4-DNP
2 forms a yellow/orange/red precipitate
3 dissolve in hot ethanol, filter, cool and allow to recrystallise
4 filter, dry, measure crystals melting point
5 compare melting point with known values in data book
reduction of carbonyl compounds
LiAlH4
dry ether
aldehyde -> 1° alcohol
keytone -> 2° alcohol
oxidation of carbonyl compounds
K2Cr2O7
H2SO4
aldehyde -> carboxylic acid
keytones not (easily) oxidised
why don’t aldehydes/keytones have H bonding within their molecules
they don’t have a O-H bond in the molecule
why is this the order of boiling points
alcohols>aldehydes/keytones>alkanes
alkanes only have london forces
aldehydes and keytones have london forces and permanent dipole forces
alcohols have london forces and H bonding which require the most energy to overcome
where and what charges is the permanent dipole on an aldehyde/keytone
delta + on the C
delta - on the O
— C (+) == O (-)
why do carbonyl compounds form hydrogen bonds with water
lone pair of electrons on the == O forms a H bond with the H in the water molecule
test with Fehlings solution (or benedict’s solution)
aldehyde gives red precipitate
keytone does not
test with tollens reagent
silver mirror
with aldehyde
test potassium dichromate and sulfuric acid
orange —> green
aldehyde
1° or 2° alcohol
what are aldehydes reduced to
1° alcohol
what are aldehydes oxidised to
carboxylic acids
what are keytones reduced to
2° alcohol
