carbonyl compounds Flashcards

1
Q

test for the carbonyl group

A

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

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2
Q

test for the aldehyde group

A

reaction with iodine in alkali
forms a yellow/cloudy precipitate

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3
Q

method to distinguish between keytone and aldehyde (using DNP)

A

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

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4
Q

reduction of carbonyl compounds

A

LiAlH4
dry ether

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

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5
Q

oxidation of carbonyl compounds

A

K2Cr2O7
H2SO4

aldehyde -> carboxylic acid
keytones not (easily) oxidised

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6
Q

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

A

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

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7
Q

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

A

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

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8
Q

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

A

delta + on the C
delta - on the O

— C (+) == O (-)

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9
Q

why do carbonyl compounds form hydrogen bonds with water

A

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

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10
Q

observation test with Fehlings solution (or benedict’s solution)

A

aldehyde gives red precipitate
keytone does not

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11
Q

test with tollens reagent

A

silver mirror
with aldehyde

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12
Q

what does potassium dichromate and sulfuric acid produces results with (and what is the observation)

A

orange —> green
aldehyde
1° or 2° alcohol

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13
Q

what are aldehydes reduced to

A

1° alcohol

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14
Q

what are aldehydes oxidised to

A

carboxylic acids

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15
Q

what are keytones reduced to

A

2° alcohol

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16
Q

what do keytones produce with gringard reagent

A

3° alcohol

17
Q

what do aldehydes produce with gringard reagents

A

1° or 2° alcohol

18
Q

what is a gringard reagent

A

a halogenoalkane and Mg

19
Q

formula of a gringard reagent

A

RMgX

20
Q

what could X be in a gringard reagent

A

Br or I

21
Q

dipole on a gringard reagent

A

C delta -
MgX delta +

22
Q

are gringard reagents reducing or oxidising agents

A

reducing (electron donor)

23
Q

Preparation of gringard reagents

A

Mg + R-X
dry ether

24
Q

why are gringard reagents prepared in dry ether

A

otherwise react explosively with water

25
Q

steps of reaction of carbonyl compounds with gringard reagents

A

1 addition reaction (anhydrous conditions)
2 hydrolysis in presence of dilute acid

26
Q

what group(s) does the iodoform test identify

A

CH3C=O group
CH3CH(OH) group

27
Q

what is a positive result for the iodoform test

A

yellow precipitate