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💊🧪Chemistry-Emma🧪💊 > Carbonyls (26) > Flashcards

Carbonyls (26) Flashcards

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1
Q

What are carbonyls?

A

Carbonyl compounds have a C=O functional group so aldehydes and ketones are both carbonyls

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2
Q

What is the functional group of an aldehyde?

A

R-C=O

H

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3
Q

What is the functional group of a ketone?

A

R - C = O

R

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4
Q

What is the product formed in the oxidation of aldehydes?

A

Aldehydes are oxidised with acidified potassium dichromate under reflux to form a carboxylic acid

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5
Q

What are the similarities and difference between the C=C bond and the C=O bond?

A

Both of them have a sigma and pi bond so you would expect them to react in the same way, however they react differently.

  • Alkenes are non-polar so they are attacked by electrophiles and undergo electrophilic additions
  • C=O is polar so the carbon is partially positive and the oxygen is partially negative. This makes it susceptible to nucleophiles attacking the carbon.
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6
Q

What kind of mechanism do carbonyls undergo?

A

Nucleophilic additions

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7
Q

What happens when you reduce an aldehyde?

A

The aldehyde reacts with a reducing agent and forms a primary alcohol

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8
Q

What is the reducing agent that reduces carbonyls?

A

NaBH4 and it usually has to be warm

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9
Q

What happens when you reduce a ketone?

A

The ketone reacts with the reducing agent to form a secondary alcohol

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10
Q

How do you increase the carbon chain of carbonyls?

A

You add HCN which is hydrogen cyanide and this makes a hydroxynitrile.

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11
Q

Why is it not safe to undergo this reaction without special equipment?

A

HCN is a colourless very poisonous liquid that boils slightly above room temperature so cannot be used safely

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12
Q

What kind of reaction is carbonyl + HCN

A

An addition reaction

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13
Q

What are the conditions and reagents needed?

A
  • Needs to be under reflux

- Needs to have H2SO4 and NaCN

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14
Q

Describe the nucleophilic addition of propanone

A
  • NaBH4 is the reducing agent and contains H- which is the nucleophile.
  • The lone pair on the H- ion is attracted to the partially positive carbon on the carbonyl
  • A dative covalent bond is then formed as it donates the electron pair to the carbon
  • This breaks the pi bond by heterolytic fission and forms a negatively charged intermediate
  • The negative oxygen donates a lone pair to hydrogen on the water to form a hydroxyl group on the intermediate and an OH-
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15
Q

How do you test for carbonyls?

A

You must add Bradys reagent which is 2,4 DNPH and this turns yellow when a carbonyl is present

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16
Q

Why must you use Brady’s reagent and not solid DNPH?

A

Because if it’s solid it can explode, so instead you dissolve it in methanol and sulphuric acid to make Bradys reagent which is safer

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17
Q

How do you distinguish between an aldehyde and a ketone once you have identified the carbonyl?

A

You perform a silver mirror test using Tollens reagent which is aqueous silver nitrate and the aldehyde will produce a silver mirror precipitate.

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18
Q

Why do aldehydes turn silver during the silver mirror test?

A

Tollens reagent contains silver ions and they act as an oxidising agent to ammonia. But they are reduced when an aldehyde is oxidised to a carboxylic acid

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19
Q

What is the functional group of carboxylic acids?

A

R - C =O

OH

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20
Q

What is the solubility of carboxylic acids like?

A

Carboxylic acids are soluble in water if they are up to 4 carbons and this is because both their C=O and OH groups are polar so can form hydrogen bonds with the water.

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21
Q

What happens to the solubilty of carboxylic acids when the carbon chain increases?

A

When the carbon chain increases, the solubilty will decrease because the non-polar carbon chain will have a great effect on the overall polarity

22
Q

What strength are carboxylic acids?

A

They are weak acids as they partially dissociate in water to form an H+.

23
Q

What kind of reactions can carboxylic acids undergo?

A

They can undergo neutralisation reactions with bases like (hydroxides, carbonates and metal oxides). They can also undergo redox reactions with metals

24
Q

What is formed during these reactions?

A

Carboxylates are formed which are salts

25
Q

Describe what happens when a carboxylic acid reacts with a metal

A

A redox reaction takes place and a carboxylate salt and hydrogen gas are formed.

26
Q

What would you observe when a carboxylic acid reacted with a metal

A

Effervescence because of the hydrogen gas and the metal disappearing

27
Q

Describe what happens when a carboxylic acid reacts with a metal oxide

A

A neutralisation takes place and carboxylate salt is formed as well as water.

28
Q

Describe what happens when a carboxylic acid reacts with an alkali?

A

A neutralisation takes place and a metal carboxylate salt with water is formed

29
Q

Describe what happens when a carboxylic acid reacts with a carbonate?

A

A neutralisation takes place and a metal carboxylate, water and carbon dioxide are formed

30
Q

What would you observe when a carboxylic acid reacts with a carbonate?

A

Effervescence (bubbles)

31
Q

How do you distinguish carboxylic acids?

A

You react them with carbonates as they are the only organic compound that is acidic enough to neutralise carbonates. This is good for distinguishing between phenol and carboxylic acids because phenols cannot neutralise carbonates

32
Q

What is a derivative of a carboxylic acid?

A

It is a compound that can be hydrolysed (water added) to form a parent carboxylic acid.

33
Q

What do all derivatives of carboxylic acids have in common?

A

They all have acyl groups which are R - C=O

34
Q

Name all the carboxylic acid derivatives

A
  • Esters
  • Acyl chlorides
  • Acid anhydride
  • Amide
35
Q

Describe how to name esters

A
  • Find the parent carboxylic acid name e.g. ethanoic acid
  • Remove the -oic off the end and put -anoate e.g ethanoate
  • Look at what is attached to the O and add that at the beginning
36
Q

Describe how to name acyl chlorides

A
  • Find the name of the parent carboxylic acid

- Remove the -oic and add -oyl chloride

37
Q

How is the acid anhydride formed and how do you name it?

A

The acid anhydride is just two carboxylic acids combined with the water removed from it. You look at how many carbons in each of the carboxylic acids and that helps you determine the prefix e.g ethanoic anhydride

38
Q

What happens during esterification?

A

A carboxylic acid and an alcohol combine and undergo a condensation reaction to form an ester. You need sulphuric acid as a catalyst

39
Q

What is hydrolysis?

A

The breakdown of a compound in the presence of water, so water is added in

40
Q

What is acid hydrolysis?

A

The reverse of esterification. You take an ester and break it down in the presence of water to form a carboxylic acid and an alcohol

41
Q

What are the conditions for acid hydrolysis?

A

You need to heat the ester under reflux with dilute acid as a catalyst

42
Q

What is alkaline hydrolysis?

A

This is called saponification and is irreversible. As ester is heated under reflux with aqueous hydroxide ions and it forms a carboxylate salt and an alcohol

43
Q

How do you prepare acyl chlorides?

A

You react the parent carboxylic acid with thionyl chloride (SOCl2) to form the acyl chloride as well as SO2 and HCl

44
Q

What conditions do you need to prepare acyl chlorides?

A

You need it to be prepared in a fume cupboard because the SO2 and HCl are released as gases that are very harmful and shouldn’t be inhaled

45
Q

How do you form esters from acyl chlorides?

A

React the acyl chloride with alcohol or with phenol

46
Q

What happens when you react acyl chlorides with alcohol?

A

An ester will be formed as well as hydrogen chloride

47
Q

What happens when you react carboxylic acids with phenols?

A

Nothing because carboxylic acids aren’t reactive enough to form esters with phenol.

48
Q

What happens when you react acyl chlorides with phenols?

A

It will form a phenyl ester and it doesn’t need any catalyst

49
Q

What happens when you react acyl chlorides with water

A

They form carboxylic acids and hydrogen chloride. It is a violent reaction and produces steamy HCl fumes so needs to be in a fume cupboard

50
Q

What happens when you react an acyl chloride with ammonia

A

You form a primary amide because it’s attached to one C and 2 Hs. You also form ammonium chloride

51
Q

What happens if you want to form a secondary amide?

A

You react an acyl chloride with a primary amine and you get a secondary amide written with N and a methylammonium chloride

52
Q

What are reactions of acid anhydrides like?

A

They undergo the same reactions as acyl chlorides but are less reactive so are useful for lab preparations when acyl chlorides may be too reactive

💊🧪Chemistry-Emma🧪💊 (25 decks)

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