A2- Aldehydes and Ketones Flashcards

1
Q

What is a carbonyl group?

A

C=O

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2
Q

Where is the carbonyl group in an aldehyde?

A

At the end of the C chain

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3
Q

Where is the carbonyl group located on a ketone?

A

in the middle of the C chain

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4
Q

What are aldehydes oxidised to?

A

carboxylic acids

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5
Q

What is butanal oxidised to?

A

Butanoic acid

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6
Q

What are ketones oxidised to?

A

NOTHING

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7
Q

What test can be used to distinguish between an aldehyde and a ketone?

A

Tollens’ -> positive for aldehyde = silver mirror

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8
Q

Why does Tollens’ reagent allow you to distinguish between aldehydes and ketones?

A

aldehydes can be oxidised, so can act as the reducing agent for [Ag(NH3)2], so it essentially becomes Ag.

Ketones cannot be reduced, so there is no change

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9
Q

What reducing agent is used to reduce aldehydes and ketones?

A

NaBH4 (sodium tetrahydrifoborate)

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10
Q

What is the nucleophile in the reducing agent used in the nucleophilic addition of aldehydes and ketones?

A

the :H- in the NaBH4

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11
Q

What happens to the lone pair on the oxygen atom (in the intermediate stage)?

A

the electrons are donated to a H+, which forms an alcohol

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12
Q

Where is the - drawn on a cyanide ion?

A

on the C
:-CN

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13
Q

What can be added as a source of :-CN ions?

A

KCN

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14
Q

Why can nucleophilic attack happen on carbonyl groups?

A

due to the difference in electronegativity between C and O

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15
Q

What is formed when an aldehyde or ketone reacts with KCN?

A

a hydroxynitrile
(eg. 2-hydroxybutanenitrile)

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16
Q

How would you oxidise an aldehyde?

A

heat with K2Cr2O7 under reflux (forms COOH, turns orange to green)

17
Q

Why aren’t ketones readily oxidised but aldehydes are?

A

as no H readily available

18
Q

Why doesn’t NaBH4 reduce C=C?

A
  • H- atom
  • C=C is electron dense
  • so repulsion