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Organic Chemistry > Compounds containing the carbonyl group > Flashcards

Compounds containing the carbonyl group Flashcards

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1
Q

List the key organic compounds that the carbonyl group is present in

A
  • Aldehydes
  • Ketones
  • Carboxylic acids
  • Esters
  • Acyl Chlorides
  • Acid anhydrides
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2
Q

Describe the polarity of carbonyl compounds and how this affects melting and boiling points

A
  • The carbonyl group is strongly polar
  • This means that permanent dipole-dipole forces form between molecules.
  • These forces mean that boiling points are higher than those alkanes of comparable relative molecular mass, but not as high as alcohols, where hydrogen bonding can occur between the molecules.
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3
Q

Describe the solubility of aldehydes and ketones

A
  • Shorter chain aldehydes and ketones mix completely with water because hydrogen bonds form between the oxygen of the carbonyl compound and water.
  • As the length of the carbon chain increases, the carbonyl compound becomes less soluble in water due to the part of the molecule that can hydrogen bond being a smaller percentage of the larger molecule.
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4
Q

What are the most common reactions involving carbonyl compounds

A

Nucleophilic additions

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5
Q

Why are nucleophilic addition reactions the most common reaction of the carbonyl groups

A
  • The polarity of the C=O bond means that nucleophilic reagents can attack the delta positive carbon atom.
  • Also, since they contain a double bond, carbonyl compounds are unsaturated which means addition reactions are possible.
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6
Q

Describe the conditions required for the nucleophilic addition of hydrogen cyanide to an aldehyde or ketone

A
  • Sodium/potassium cyanide are used as the source of cyanide ions.
  • Dilute hydrochloric acid is then added to provide the H+ ion.
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7
Q

What are the products of the nucleophilic addition of hydrogen cyanide to aldehydes or ketones

A

Hydroxynitriles

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8
Q

Why are hydroxynitriles and the nucleophilic addition reaction that forms them useful

A
  • They are useful in synthesis because both the -OH and -CN groups are reactive and can be converted into other functional groups.
  • The reaction is also useful in organic synthesis because it increases the length of the carbon chain by one carbon.
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9
Q

In terms of optical isomerism, what does the nucleophilic addition of hydrogen cyanide to an aldehyde or unsymmetrical ketone produce and why

A
  • A racemic mixture
  • This is because the CN- ion can attack from above or below the flat C=O group.
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10
Q

Can Ketones be oxidised to carboxylic acids

A
  • No
  • Ketones cannot be oxidised easily to carboxylic acids because it would require a C-C bond to be broken due to the oxygen being in the middle of the molecule.
  • Even if this does happen, the result is a shorter chain molecule, carbon dioxide and water, not a carboxylic acid.
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11
Q

What is the reagent that oxidised aldehydes to carboxylic acids

A

Acidified (with dilute sulfuric acid) potassium dichromate

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12
Q

Describe Fehlings test

A
  • Fehlings contains the blue Cu2+ ion
  • when an aldehyde is warmed with Fehlings solution, a brick red precipitate of copper (I) oxide is produced as the copper (II) oxidised the aldehyde to a carboxylic acid and is itself reduced to copper (I).
  • Ketones give no reaction to this test.
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13
Q

Describe the silver mirror test

A
  • The silver mirror test uses Tollens reagent which is formed when aqueous ammonia is added to an aqueous solution of silver nitrate.
  • when an aldehyde is warmed with Tollens reagent, metallic silver is formed as the aldehyde is oxidised to a carboxylic acid.
  • a silver mirror on the inside of the test tube forms.
  • Ketones give no reaction to this test
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14
Q

What are the two chemical tests that distinguish between an aldehyde and a ketone

A

Fehlings and the silver mirror test

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15
Q

What reaction do Fehlings and the silver mirrr test use to distinguish between aldehydes and ketones

A
  • The oxidation of aldehydes.
  • the fact that ketones cannot be oxidised
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16
Q

What happens when a reducing agent reacts with an aldehyde or ketone

A

The aldehydes and ketones will be reduced to alcohols

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17
Q

Give an example of a reducing agent that will reduce aldehydes and ketones, what it does and how it works

A
  • Sodium tetrahydridoborate (III), NaBH4 in aqeous solution
  • This generates the nucleophile :H-, the hybride ion.
  • This works because it is attracted to the delta positive C of the C=O bond
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18
Q

Why does sodium tetrahydroborate (III) NaBH4 reduce the C=O but not C=C

A

It is repelled by the high electron density in the C=C bond but is attracted to the delta positive C of the C=O bond

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19
Q

Where does the H+ ion used in the reduction of an aldehyde or ketone come from

A

The solvent (acidic solvent)

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20
Q

Where does the :H- ion involved in the reduction of an aldehyde or ketone come from

A

The reducing agent (eg NaBH4)

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21
Q

What type of reaction is the reduction of aldehydes and ketones back into alcohols and why

A
  • Nucleophilic addition
  • This is because the H- ion is a nucleophile
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22
Q

What two functional groups does a carboxylic acid contain

A
  • The carbonyl group (C=O)
  • The hydroxyl group -OH
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23
Q

Is the carbon from the COOH is carboxylic acids included in the acids name

A

Yes. This carbon counts towards the number used for naming the acid.

24
Q

What is the main difference in the properties of the -OH group in alcohols compared to carboxylic acids

A

The -OH group in carboxylic acids is much more acidic than the -OH group in alcohols

25
Q

How does the naming of carboxylic acids work when the functional group is attached to a benzene ring

A
  • the suffix -carboxylic acid is used instead of oic acid.
  • The carbon of the functional group is not counted as part of the root.
26
Q

Describe the solubility of carboxylic acids in water

A
  • The carboxylic acid group can form hydrogen bonds with water molecules.
  • Therefore carboxylic acids up to and including four carbons are completely soluble in water.
27
Q

Describe the melting points of carboxylic acids

A
  • Carboxylic acids form hydrogen bonds with one another in the solid state.
  • This means that they have much higher melting points than the alkanes of similar relative molecule mass.
28
Q

Describe what an ester is

A
  • Esters are derived from carboxylic acids.
  • The hydrogen from the COOH group is replaced by an alkyl or aryl group meaning the OH is replaced by OR
  • Their general formula is RCOOR’.
29
Q

Describe the key properties of short chain esters

A
  • short chain esters are fairly volatile and have pleasant fruity smells, meaning the at they are often used in flavourings and perfumes.
  • They are also used as solvents and plasticisers.
30
Q

What are esters with long carbon chains

A

Fats and oils

31
Q

Describe what happens when a carboxylic acid loses the H+ from the -OH group (loses a proton)

A
  • If the hydrogen of the -OH group is lost, the negative carboxylate ion is left
  • The negative charge is shared over the whole of the carboxylate group.
  • This delocalisation makes the resulting ion more stable.
  • This means that carboxylic acids are weak acids, meaning the equilibrium is way over to the left (not as many acids that have lost the proton exist as those that have it).
32
Q

What happens when carboxylic acids react with sodium hydrogencarbonate (NaHCO3)

A
  • They release carbon dioxide
  • This distinguishes them from other organic compounds that contain the -OH group, such as alcohols.
33
Q

Describe how carboxylic acids react

A
  • Carboxylic acids are proton donors and show typical reactions of acids.
  • They form ionic salts with the more reactive metals, alkalis, metal oxides, or metal carbonates in the usual way.
  • The salts have the general name carboxylates and are named from the particular acid.
34
Q

How are esters formed

A
  • Carboxylic acids react with alcohols to form esters.
  • The general word equation is : alcohol+ carboxylic acid—> ester+ water.
  • This reaction is sped up by a strong acid catalyst.
  • This is a reversible reaction and forms an equilibrium mixture of reactants and products.
35
Q

Describe the hydrolysis of esters

A
  • The carbonyl of an ester has a delta positive charge and is therefore attacked by water acting as a weak nucleophile.
  • This is the reverse reaction to the formation of esters from a carboxylic acid and alcohols.
  • The hydrolysis of esters does not go to completion.
  • Instead, it produces an equilibrium mixture containing the ester, water, acid (catalyst) and alcohol.
36
Q

What happens when bases are used as catalysts to the hydrolysis of esters instead of an acid

A
  • The salt of the acid is produced rather than the acid itself.
  • This removes the acid from the reaction mixture so an equilibrium is not established and the reaction goes to completion, so there is more product in the mixture.
37
Q

What are fats and oils

A

-Triglycerides
- Esters of the alcohol propane-1,2,3-triplets (glycerol)

38
Q

What is the difference between days and oils

A

Oils are liquids at room temperature whereas fats are solid.

39
Q

What happens when days and oils are hydrolysed

A

A molecule of glycerol and the component fatty acids are produced

40
Q

What does the hydrolysis of triglycerides (fats and oils) by boiling with sodium hydroxide produce

A

Glycerol and sodium salts of the three acids which formed part of the ester. Both of these are useful products.

41
Q

Why are the sodium salts of fatty acids produced during the hydrolysis of triglycerides by boiling with sodium hydroxide useful

A
  • The salts are soaps
  • Sodium salts are ionic and dissociate to form Na+ and RCOO-.
  • RCOO- has two distinct ends: a long hydrocarbon chain which is non-polar (hydrophobic) and a COO- group which is polar and ionic.
  • The hydrocarbon will mix with grease while there COO- mixes with water.
  • This makes these molecules good cleaning agents.
42
Q

What is a key property of glycerol that makes it very useful

A

Glycerol contains three O—H bonds which means it readily forms hydrogen bonds and is soluble in water.

43
Q

List the key uses of glycerol

A

1) Pharmaceutical and cosmetic preparations: this is because it attracts water so is used to prevent creams and ointments from drying out.
2) It is used as a solvent in many medications and in the food industry. For example, it is present in toothpastes and food colourings
3) It is used to plasticise various materials like sheets and gaskets, cellophane and special quality papers.

44
Q

What is acylation

A

The process by which the acyl group is introduced into another molecule.

45
Q

What are acid derivatives and give some examples

A
  • A group of compounds which all have the actual group as part of their formula.
  • Examples: acid anhydrides, acyl chlorides and carboxylic acids.
46
Q

Summarise how acylation occurs (nucleophilic addition-elimination)

A
  • A nucleophile attacks the delta positive C in the carbonyl group.
  • In the process the nucleophile replaces Z (the leaving group) and the nucleophile therefore acquired an acyl group.
  • This means that the nucleophile has been acylated.
47
Q

What three factors determine how quickly the acylation (nucleophilic addition-elimination) reaction occurs

A

1) The magnitude of the delta positive charge on the carbonyl carbon, which in turn depends on the electron-releasing or attracting power of Z.
2) How easily Z (leaving group) is lost.
3) How good the nucleophile is.

48
Q

Describe how acyl chlorides and acid anhydrides are good acylating agents

A
  • The Z groups of acyl chlorides and acid anhydrides withdraw electrons from the carbonyl carbon.
  • This makes the carbon more positive and makes these compounds reactive towards nucleophiles which makes them good acylating agents.
  • Acyl chlorides are somewhat more reactive than acid anhydrides.
49
Q

Define nucleophile

A

Lone pair donor

50
Q

List the key nucleophiles that acyl chlorides and acid anhydrides react with in descending order of reactivity

A
  • Primary amine
  • Ammonia
  • Alcohol
  • Water
51
Q

What happens to the hydrogen atom in the nucleophiles during nucleophilic addition-elimination reactions

A
  • The nucleophiles are all neutral so they must lose a hydrogen ion during the reaction.
  • One way of looking at these reactions is that a hydrogen atom of the nucleophile has been replaced by an acyl group.
52
Q

During acylation (nucleophilic addition-elimination), if the nucleophile is ammonia what product is formed

A

An amide

53
Q

During acylation (nucleophilic addition-elimination), if the nucleophile is a primary amine, what product is formed

A

An N-substituted amide

54
Q

During acylation (nucleophilic addition-elimination), if the nucleophile is the -OH group of an alcohol what product is formed

A

An ester

55
Q

During acylation (nucleophilic addition-elimination), if the nucleophile is the OH in water, what product is formed

A

A carboxylic acid

56
Q

What are the advantages of ethanoic anhydride over ethanoyl chloride as an acylating agent

A
  • it is cheaper
  • it is less corrosive
  • it does not react with water as readily
  • it is safer, as the by product of its reaction is ethanoic acid rather than hydrogen chloride
  • one important use is in the production of aspirin

Organic Chemistry (14 decks)

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