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
observation test with Fehlings solution (or benedict’s solution)
aldehyde gives red precipitate
keytone does not
test with tollens reagent
silver mirror
with aldehyde
what does potassium dichromate and sulfuric acid produces results with (and what is the observation)
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
what do keytones produce with gringard reagent
3° alcohol
what do aldehydes produce with gringard reagents
1° or 2° alcohol
what is a gringard reagent
a halogenoalkane and Mg
formula of a gringard reagent
RMgX
what could X be in a gringard reagent
Br or I
dipole on a gringard reagent
C delta -
MgX delta +
are gringard reagents reducing or oxidising agents
reducing (electron donor)
Preparation of gringard reagents
Mg + R-X
dry ether
why are gringard reagents prepared in dry ether
otherwise react explosively with water
steps of reaction of carbonyl compounds with gringard reagents
1 addition reaction (anhydrous conditions)
2 hydrolysis in presence of dilute acid
what group(s) does the iodoform test identify
CH3C=O group
CH3CH(OH) group
what is a positive result for the iodoform test
yellow precipitate
