carbonyl compounds

Question 1

test for the carbonyl group

Answer 1

add 2,4-DNP solution
gives an orange/yellow/red precipitate

Question 2

test for the aldehyde group

Answer 2

reaction with iodine in alkali
forms a yellow/cloudy precipitate

Question 3

method to distinguish between keytone and aldehyde (using DNP)

Answer 3

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

Question 4

reduction of carbonyl compounds

Answer 4

LiAlH4
dry ether

aldehyde -> 1° alcohol
keytone -> 2° alcohol

Question 5

oxidation of carbonyl compounds

Answer 5

K2Cr2O7
H2SO4

aldehyde -> carboxylic acid
keytones not (easily) oxidised

Question 6

why don’t aldehydes/keytones have H bonding within their molecules

Answer 6

they don’t have a O-H bond in the molecule

Question 7

why is this the order of boiling points
alcohols>aldehydes/keytones>alkanes

Answer 7

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

Question 8

where and what charges is the permanent dipole on an aldehyde/keytone

Answer 8

delta + on the C
delta - on the O

— C (+) == O (-)

Question 9

why do carbonyl compounds form hydrogen bonds with water

Answer 9

lone pair of electrons on the == O forms a H bond with the H in the water molecule