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Organic Chemistry > 3.8 Aldehydes and Ketones > Flashcards

3.8 Aldehydes and Ketones Flashcards

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1
Q

What are carbonyls?

A

Compounds with a C=O bond.

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2
Q

If the C=O is on the end of a chain with a H attached what is the compound?

A

Aldehyde

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3
Q

If the C=O is in the middle of the chain what is the compound?

A

Ketone

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4
Q

Are carbonyls soluble in water?

A

The Smaller carbonyls are soluble in water because they can form hydrogen bonds with water.

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5
Q

Why is the C=O bond polarised?

A

O is more electronegative than carbon. The positive carbon atom attracts nucleophiles.

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6
Q

What are aldehydes oxidised to?

A

Primary alcohol —> Aldehyde —> Carboxylic acid

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7
Q

What are ketones oxidised to?

A

Secondary alcohols —> Ketones —>do not oxidise

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8
Q

What are the reagents and conditions needed for aldehydes to oxidise to carboxylic acids?

A

Reagent: Potassium dichromate (VI) solution and dilute sulfuric acid.

Conditions: heat under reflux.

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9
Q

How else can aldehydes be oxidised?

A

Using Fehling’s solution or Tollins reagent. These are used as tests for the presence of aldehyde groups

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10
Q

What conditions are needed for aldehydes to react with Tollens Reagent?

A

heat gently

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11
Q

What is the observation of the reaction between Tollens and aldehydes?

A

with aldehydes, a silver mirror forms coating the inside of the test tube. Ketones result in no change.

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11
Q

How do Tollens and aldehydes react?

A

Aldehydes only oxidise by Tollens’ reagent into a carboxylic acid. The silver ions are reduced to silver atoms in the Tollens’.

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11
Q

What conditions are needed for aldehydes to react with Fehling’s solution?

A

heat gently

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12
Q

How do Fehling’s and aldehydes react?

A

aldehydes only are oxidised by Fehling’s Solution into a carboxylic acid. The copper (II) ions are reduced to copper(I) oxide.

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13
Q

What is the observation of the reaction between Fehling’s and aldehydes?

A

Aldehydes :Blue Cu 2+ ions in solution change to a red precipitate of Cu2O. Ketones do not react.

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14
Q

What conditions and reagents are needed for the reduction of carbonyls?

A

Reagents: NaBH4 In aqueous ethanol

Conditions: Room temperature and pressure

15
Q

What do reagents such as NaBH4 and LiAIH4 reduce carbonyls to?

A

alcohols

16
Q

What to aldehydes reduce to?

A

Primary alcohols

17
Q

What do ketones reduce to?

A

Secondary alcohols

18
Q

Draw the equation of the reduction of propanal.

A
19
Q

Draw and name the mechanism when propanone reacts with NaBH4.

A
20
Q

Draw the equation of the reduction of propanone.

A
21
Q

Carbonyls can also be reduced using catalytic hydrogenation what reagent and conditions are needed?

A

Reagent: hydrogen and nickel catalyst

Conditions: high pressure

22
Q

What is the reagent, conditions and name of the mechanism for the Addition of hydrogen cyanide to carbonyls to form hydroxynitriles?

A

Reagent: sodium cyanide (NaCN) and dilute sulfuric acid.

Conditions: Room temperature and pressure

Mechanism: nucleophilic addition

23
Q

What happens when naming hydroxy nitriles?

A

When naming hydroxy nitriles the CN becomes part of the main chain and carbon no 1

23
Q

Why is KCN toxic?

A

because of cyanide ion.

24
Q

What are the advantages of using KCN or NaCN?

A

An advantage of using KCN or NaCN is that there will be a higher concentration of the CN- ion as these compounds will completely ionise. HCN is a weak acid an will only partially ionise

25
Q

Draw and name the mechanism of the addition of hydrogen cyanide to propanone to form hydroxynitriles.

A
26
Q

What is the result of the Nucleophilic addition of HCN to aldehydes and ketones (unsymmetrical) when the trigonal planar carbonyl is approached from both sides by the HCN attacking species?

A

Formation of a racemate

Organic Chemistry (17 decks)

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