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Y13 MDY Organic Topic 2 - Aldehydes and Ketones > Aldehydes and Ketones > Flashcards

Aldehydes and Ketones Flashcards

1
Q

Aldehydes and ketones are carbonyls. What is a carbonyl group?

A

C=O A carbon with a double bond to an oxygen

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2
Q

If the C=O is on the end of the chain with an H attached, what homologous series is present?

A

aldehyde

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3
Q

If a carbonyl is present in the middle of a carbon chain and has alkyl groups to both sides, which homologous series is present?

A

Ketone

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4
Q

What are the strongest kind of intermolecular forces present in aldehydes and ketones?

A

permanent dipole interactions

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5
Q

Why is the carbonyl group polarised?

A

The C=O bond is polarised because oxygen is more electronegative than carbon

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6
Q

Why does the carbonyl group in aldehydes and ketone react?

A

The positive carbon atom attracts nucleophiles.

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7
Q

What is a nucleophile?

A

Electron pair donor

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8
Q

Which oxidising agent is used to oxidise aldehydes and ketones?

A

acidified potassium dichromate solution OR (H+(aq) / K2Cr2O7(aq))

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9
Q

What can primary alcohols be oxidised to?

A

Primary alcohol → aldehydes → carboxylic acid

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10
Q

What are the conditions to oxidise a primary alcohol to an aldehyde?

A

excess alcohol; acidified potassium dichromate; distillation of product

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11
Q

What do you see when acidified potassium dichromate succesfully oxidises a carbonyl compound?

A

Colour change of orange to green

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12
Q

What are the conditions to oxidise an alcohol or aldehyde to a carboxylic acid?

A

heat under reflux; acidified potassium dichromate

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13
Q

Which acid can be used to acidify potassium dichromate?

A

dilute suphuric acid

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14
Q

What product is formed when you oxidise a secondary alcohol with acidified potassium dichromate?

A

ketone

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15
Q

What product is formed when you oxidise a tertiary alcohol with acidified potassium dichromate?

A

no reaction

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16
Q

What is Tollens Reagent?

A

Tollen’s reagent is formed by mixing aqueous ammonia and silver nitrate.

17
Q

What is the active part of Tollens’ Reagent?

A

The active substance is the complex ion of [Ag(NH3)2]+ .

18
Q

What do you see if Tollens Reagent acts as an oxidising agent?

A

a silver precipitate is formed

19
Q

Give an equation for Tollens reagent acting as an oxidising agent

A

Ag+(aq) + e- → Ag (s)

20
Q

Do aldehydes and/or ketones react with Tollens?

A

Just aldehydes (they are oxidised by the Tollens to form carboxylic acids - ketones can’t be oxidised)

21
Q

What ions are present in Fehlings Reagent?

A

blue Cu 2+ ions.

22
Q

Which substances are oxidised by Fehlings?

A

Just aldehydes (they are oxidised to form carboxylic acids - ketones can’t be oxidised)

23
Q

What do you observe when Fehlings oxidises an aldehyde?

A

blue solution forms a red/brown precipitate of Cu+ oxide (Cu2O)

24
Q

Name a reducing agent that can reduce an aldehyde to a primary alcohol?

A

NaBH4 In aqueous ethanol. Room temp and pressure.

25
Q

Name a reducing agent that can reduce a carboxylic acid to a primary alcohol?

A

NaBH4 In aqueous ethanol. Room temp and pressure.

26
Q

Name a reducing agent that can reduce a ketone to a secondary alcohol?

A

NaBH4 In aqueous ethanol. Room temp and pressure.

27
Q

Give a balanced equation for the reduction of propanal. What are the conditions?

A

Conditions: NaBH4 in aqueous ethanol

28
Q

Give a balanced equation for the reduction of propanone. What are the conditions?

A

Conditions: NaBH4 in aqueous ethanol.

29
Q

Give the mechanism for the reduction of propanone.

A
30
Q

Nae the mechanism

A

Nucleophilic substitution.

31
Q

What are the conditions for catalytic hydrogenation?

A

Reagent: hydrogen (H2(g)) and nickel catalyst (Ni)

Conditions: high pressure

32
Q

Give the mechanism for the addition of cyanide ions to carbonyls

A
33
Q

Name the mechanism for the addition of cyanide ions to carbonyls

A

Nucleophilic substitution

34
Q

What are the conditions for nucleophilic additions of CN- to carbonyls?

A

Reagent: sodium or potassium cyanide (NaCN or KCN) and dilute sulfuric acid.
Conditions: Room temperature and pressure

35
Q

Why do chemists use H+/KCN and not HCN to make hydroxynitriles?

A

HCN is a toxic gas that is difficult to contain. The KCN is still toxic but it is a solution.

36
Q

Why does nucleophilic addition of HCN to unsymmetrical carbonyls results in the formation of a racemate?

A

The carbonyl bond is planar.

it can be attacked from above or below by CN- with an equal chance.

This means that both enantiomers are formed in equal amounts.

Y13 MDY Organic Topic 2 - Aldehydes and Ketones (1 decks)

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