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Bellas chemistry > Topic 17.2 Carbonyl compounds > Flashcards

Topic 17.2 Carbonyl compounds Flashcards

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1
Q

Carbonyl group

A
  • A carbon atom joined by a double bond to an oxygen atom.
  • -C=O
  • Carbonyl compounds can be classed as either aldehydes or ketones.
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2
Q

Aldehydes

A
  • 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.
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3
Q

Ketone

A
  • There is only hydrocarbon groups joined to the carbonyl group.
  • Cannot be further oxidised as they do not have hydrogen atom attached to their carbonyl.
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4
Q

Bonding in carbonyl compounds

A
  • Contain -C=O group.
  • Polar bond.
  • Electron density is greater near the δ- O atom.
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5
Q

Physical properties in carbonyl compounds

A
  • 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.
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6
Q

Physical properties in ketones and aldehydes

A
  • 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.
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7
Q

Primary alcohol

A

Oxidised:
Primary alcohol —> aldehyde —>
carboxylic acid

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8
Q

Secondary alcohol

A

Oxidised:
Secondary alcohol —> ketone —> X

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9
Q

Tertiary alcohol

A

Tertiary alcohol —> X

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10
Q

Reagent observations: Felling’s reagent

A

Aldehyde: brick red, precipitate solid
Ketone: stays blue, no visible change

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11
Q

Reagent observations: Tollen’s reagent

A

Aldehyde: silver mirror, black precipitate
Ketone: stays colourless, no visible change

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12
Q

Reagent observations: sodium dichromate

A

Aldehydes: decolourises
Ketones: stays purple, no visible change

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13
Q

Reagent observations: K2Cr2O7

A

Aldehyde: colour change, orange to green
Ketone: stays orange, no visible change

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14
Q

Reaction with proponal/anone: Sodium dicromate

A

Propanal: green
Propanone: orange (no change)

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15
Q

Reaction with proponal/anone: Felling’s solution

A

Propanal: light blue
Propanone: dark blue

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16
Q

Reaction with proponal/anone: Tolling’s reagent

A

Propanal: white precipitate
Propanone: colourless

17
Q

Reduction reactions (eg. 2° alcohol –> 1° alcohol)

A

Aldehydes and ketones can be reduced to alcohols using lithium tetrahydridoaluminate (LiAlH4) dissolved in dry ether.
-Reducing agent represented by [H]

18
Q

Oxidation reactions

A

-Aldehydes can be oxidised to form carboxylic acids
-Ketones are not easily oxidised (assume they aren’t)
-Oxidising agents shown as [O]

19
Q

Reactions with iodine

A
  • Triidomethane reaction.
  • Carbonyl compound added to an alkaline solution of iodine.
  • Mixture warmed then cooled.
  • Yellow precipitate forms - this is a positive result.
  • Test for CH3CO group (found in ethanal and all methyl ketones).
20
Q

Reaction with HCN

A

-Aldehydes and ketones react with HCN in an alkaline solution of KCN
-These are addition reactions where a hydrogen atom joins to the oxygen in the carbonyl group and the cyanide group attaches to the carbon of the carbonyl group

21
Q

Naming products

A

OH group- hydroxy
CN group- nitrile
The products are known as hydroxynitriles

22
Q

Nucleophilic addition mechanism (Step 1)

A

Step 1: nucleophilic attack by a cyanide ion on the δ+ carbon atom of the carbonyl group.

23
Q

Nucleophilic addition mechanism (Step 2)

A

Step 2: the intermediate reacts with a hydrogen cyanide molecule.

24
Q

Optical activity

A
  • As C=O is planar there is an equal chance of the CN- ion attacking from each side of the plane.
  • Even though the product contains a chiral centre, the product is not optically active as there are equal amounts of each enantiomer - a racemic mixture.
25
Q

Reaction with 2,4-dinitrophenylhydrazine (Brady’s reagent)

A

A bright orange precipitate indicates the presence if a carbonyl compound.

26
Q

How to find the melting temperature of derivatives

A
  • The compounds formed, known as derivatives, can be used to identify individual compounds.
  • The derivatives are purified and dried and their melting point measured.
27
Q

Reagent observations: 2,4 DNPH

A

Aldehyde: orange precipitate
Recyrstalise and find melting point to find which compound it is.

28
Q

Recrystalisation

A

1) Dissolve min hot solvent
2) Filter
3) Cool & crystalise
4) Filter with Buchner funnel
5) Wash with minimum cold solvent
6) Dry in warm oven

29
Q

Acyl chlorides

A
  • RCOCl.
  • Contain carbonyl group.
  • Replaced the oh in cooh with Cl.
30
Q

Iodoform test (triodomethane)

A

CH3CO in a molecule reacts with Iodine/OH- to form a yellow precipitate.

31
Q

Carboxylic acids reactions

A
  • Reduction - to primary alcohols.
  • Neutralisation - completely with aqueous alkali forms carboxylate salts.
  • Halogenation - OH is replaced by halogen forms aceyl halogenides.
  • Esterfication- alcohol and acid catalyst forms este.
32
Q

Esters

A
  • Naming: -thyl -oate
  • RCOOR
  • =O
  • Colourless liquids
  • Low melting and boiling
  • Insoluble in water
  • Smells of fruit
33
Q

Hydrolysis of esters

A
  • Opposite of esterification.
  • Acidic- acid speed up as a catalyst.
  • Alkaline - goes onto completion rather than equilibrium.
  • Produces carboxylate salt.
34
Q

Differences in esterfacation with oyl and carboxylic acid

A
  • Irreversable - reversable
  • HCl formed - H2O formed
  • Faster
  • No acid catalyst needed - needed
35
Q

Esther and acyl chloride reactivity

A
  • Acyl chlorides more reactive.
  • As more susceptible to attack from nucleophiles.
36
Q

Polyesters

A

Polymers that have monomers bonded with an ester link.

Bellas chemistry (32 decks)

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