Isomerism and Carbonyl Compounds

Question 1

What is a Chiral/asymmetric carbon?

Answer 1

It is a carbon atom that has four different groups attached to it. (can be phosphorus instead)

Question 1

What are stereoisomers?

Answer 1

Stereoisomers have the same structural formula but have their atoms arranged differently in space.

Question 2

What are optical isomers/enantiomers?

Answer 2

It is when you arrange the four different groups around a chiral carbon in two different ways. They are mirror images so they cannot be superimposed. (if they can they are achiral and therefore not optical isomers)

Question 3

What is the difference between normal light and plane polarised light?

Answer 3

Normal light vibrates in all directions. Plane-polarised light only vibrates in one direction.

Question 4

How do optical isomers and light relate?

Answer 4

Optical isomers are optically active, meaning they rotate plane polarised light. One enantiomer rotates it in a clockwise direction while the other rotates it in an anticlockwise direction.

Question 5

What is a racemate or racemic mixture?

Answer 5

It is a mixture that contains equal quantities of each enantiomer of an optically active compound. The two enantiomers cancel each other’s light-rotating effect. The mixture is usually formed when reacting two achiral things together to get a racemic mixture as there is an equal chance of forming each of the enantiomers.

Question 6

What types of reactions usually produce racemic mixtures?

Answer 6

Reactions with planar bonds like double bonds like c=c and c=o. So products of reactions that happen at the carbonyl group of aldehydes and unsymmetrical ketones are enantiomers as a racemic mixture.

Question 7

Why do Nucleophilic addition reactions with aldehydes and unsymmetrical ketones produce enantiomers?

Answer 7

The nucleophile can attack from two different directions, and that causes the formation of two different optically active compounds. There is an equal chance in each direction because the molecule is planar so equal amounts of each enantiomer are produced and therefore a racemic mixture is formed.

Question 8

Why do nucleophilic addition reactions with a symmetrical ketone not produce enantiomers?

Answer 8

If you start with a symmetrical ketone instead, you’ll make a product that doesn’t have a chiral center, so it won’t display optical isomerism.

Question 9

What are the differences between Aldehydes and Ketones?

Answer 9

Aldehydes have their carbonyl group at the end of the carbon chain so they end in -al
Ketones have their carbonyl group in the middle of the carbon chain. their names end in -one and have a number to indicate which carbon the carbonyl group is on.
Aldehydes can be easily oxidised by ketones can’t

Question 10

Do oxidizing agents react with aldehydes or ketones and why?

Answer 10

They react with aldehydes to produce carboxylic acids, but not with ketones as you would need to break a c-c bond.

Question 11

What is Tollen’s reagent?

Answer 11

Tollen’s reagent is a colorless solution of silver nitrate dissolved in aqueous ammonia.
When heated in a test tube with aldehyde, the silver ions in Tollen’s reagent are reduced to silver atoms, and a silver mirror forms.
Ketones cannot be easily oxidized to Tollen’s reagent so doesn’t react with ketones so there is no colour change.

Question 12

What is Fehling’s Reagent?

Answer 12

It is a blue solution of copper 2+ ions dissolved in sodium hydroxide.
If it is heated with an aldehyde the copper 2+ ions are reduced to a brick-red precipitate of Copper 1+ oxide.
Ketones do not react with Fehling’s solution, so no precipitate is formed.

Question 13

What is the reducing agent commonly used to reduce aldehydes and ketones back to alcohol?

Answer 13

NaBH4 (sodium tetrahydrioborate(III) or sodium borohydride) dissolved in water with methanol is usually the reducing agent used. In equations [H] is used. The H- ions come from the reducing agent.
These are nucleophilic addition reactions.

Question 14

What does potassium cyanide produce when reacted with carbonyl compounds? (what type of reaction)

Answer 14

Hydroxynitriles, It is done through a nucleophilic addition reaction.

Question 15

Why is potassium Cyanide a dangerous chemical to work with?

Answer 15

It is an irritant but is also extremely dangerous if it is ingested or inhaled. It can react with moisture to produce hydrogen cyanide, which is a highly toxic gas. To reduce any risks the person should wear gloves, and goggles, and do the experiment in a fume cupboard.

Question 16

What functional group do carboxylic acids contain?

Answer 16

They contain the carboxyl group -COOH

Question 17

Why are carboxylic acids weak acids?

Answer 17

They are weak acids as in water they partially dissociate into a carboxylate ion and an H+ ion.

Question 18

What does dissociate mean?

Answer 18

Often meaning to reversibly split into something smaller, atoms, ions, etc.

Question 19

What do carboxylic acids react with?

Answer 19

They react with carbonates to form a salt, carbon dioxide, and water

Question 20

What functional group do esters contain?

Answer 20

-COO-

Question 21

How are esters formed?

Answer 21

They are frequently made by heating a carboxylic acid with an alcohol in the presence of a strong acid catalyst (usually containing H2SO4). It is called an esterification reaction.

Question 22

What property do esters have that relates to their function in industry?

Answer 22

They have a sweet smell, varying from gluey sweet to fruity. This makes them useful in perfumes. The food industry also uses esters to flavor things like drinks and sweets too.

Question 23

What property do esters have that relates to their function in glues and printing inks?

Answer 23

They are polar liquids so lots of polar organic compounds will dissolve in them. They’ve also got quite low boiling points, so they evaporate easily from mixtures. This makes them good solvents in glues and printing inks.

Question 24

What properties do esters have that relate to their function in plastics?

Answer 24

Esters are used as plasticizers- they’re added to plastics during polymerization to make the plastic more flexible. Over time, the plasticizer molecules escape through, and the plastic becomes brittle and stiff.

Question 25

What is hydrolysis and why do you use an acid or an alkali when doing it?

Answer 25

Hydrolysis is when a substance is split up by water. Using just water is really slow so an acid or an alkali is often used to speed it up.

Question 26

What is the difference between acid hydrolysis and base hydrolysis of esters?

Answer 26

Both types make the same alcohol but the second product in each case is different.

Question 27

What is acid hydrolysis of esters?

Answer 27

It is where the ester is split into an acid and an alcohol. You have to reflux the ester with a dilute acid such as hydrochloric or sulphuric.

Question 28

What is base hydrolysis of esters?

Answer 28

It involves refluxing the ester with a dilute alkali, such as sodium hydroxide. You get a carboxylate ion and an alcohol.

Question 29

What are fatty acids, and how are they related to esters?

Answer 29

They are long-chain carboxylic acids that can be either saturated or unsaturated. When combined with glycerol they make esters (fats and oils).

Question 30

What are the properties of animal fats?

Answer 30

They have mainly saturated hydrocarbon chains. This means they fit neatly together, increasing the van der Waal forces between them. This means you need higher temperatures to melt them and they are solid at room temperature.

Question 31

What are the properties of vegetable oils?

Answer 31

They have unsaturated hydrocarbon chains- the double bonds mean the chains are bent and don’t pack together well, decreasing the Van der Waal forces. So they are easier to melt and are liquids at room temperature.

Question 32

What is a soap and how can it be formed?

Answer 32

A soap is the salt of a long-chain carboxylic acid. You can hydrolyse oils and fats by heating them with sodium hydroxide to produce glycerol, soaps, and fatty acids.

Question 33

What is a biodiesel?

Answer 33

A biodiesel is a mixture of methyl esters of fatty acids.
As vegetable oils e.g. rapeseed oil can make good fuels but can’t be burnt directly in engines they need to be converted into biodiesel first. This involves reacting them with methanol, using potassium hydroxide as a catalyst.

Question 34

What is the functional group of Acyl chlorides?

Answer 34

Acyl (acid) chlorides have the functional group COCl and all their names end in -oyl chloride

Question 35

What do Acycl chlorides produce when reacted with water?

Answer 35

It is a vigorous reaction with cold water that produces a carboxylic acid.

Question 36

What do Acycl chlorides produce when reacted with alcohols?

Answer 36

It is a vigorous reaction at room temperature that produces an ester.

Question 37

What do Acycl chlorides produce when reacted with ammonia?

Answer 37

It is a violent reaction at room temperature that produces an amide.

Question 38

What do Acycl chlorides produce when reacted with primary amines?

Answer 38

It is a violent reaction at room temperature, producing a N-substituted amide.

Question 39

What is an acid anhydride?

Answer 39

It is made from two identical carboxylic acid molecules. If you know the name of the carboxylic acid, you take away the acid and replace it with anhydride.
e.g. methanoic anhydride.

Question 40

What are the reactions of water, alcohol, ammonia, and amines with acid anhydrides?

Answer 40

They are almost the same as acyl chlorides but just less vigorously and you get a carboxylic acid formed not HCl

Question 41

Why are acyl chlorides easily susceptible to nucleophiles?

Answer 41

Both the chlorine and oxygen atoms draw electrons towards them, so the carbon has a slight positive charge and is easily attacked by nucleophiles.

Question 42

What are nucleophilic addition-elimination reactions?

Answer 42

It is a two-step process of an addition reaction followed by an elimination reaction.

Question 43

What is aspirin and how is it made?

Answer 43

Asprin is an ester and it is made by reacting salicylic acid with ethanoic anhydride or ethanoyl chloride.

Question 44

Why is ethanoic anhydride used in industry rather than ethanoyl chloride?

Answer 44

• it is cheaper than ethanoyl chloride
• it is safer to use than ethanoyl chloride as it is less corrosive, reacts more slowly with water, and doesn’t produce dangerous hydrogen chloride fumes.

Question 45

How do you use a separating funnel?

Answer 45

If a product is insoluble in water you can use separation to remove any impurities that do dissolve in water.
1) Once the reaction is completed pour the mixture into a separating funnel and add water
2) Shake the funnel and then allow it to settle. The organic layer and the aqueous layer are immiscible so separate into two different layers.
3) You can then open the tap and run each layer off into separate containers

Question 46

What is solvent extraction and when is it used?

Answer 46

Solvent extraction is used when the product and impurities are both soluble in water.
You take an organic solvent in which the product is more soluble than it is in water and you add it to the impure solution and shake well. The solvent will dissolve into the organic solvent then you can separate using a separating funnel as usual.

Question 47

How can you remove water from a product?

Answer 47

By drying it
1) After using a separating funnel the product will contain traces of water
2) Use an anhydrous salt such as magnesium sulfate or calcium chloride. The salt is used as a drying agent- it binds to any water present to become hydrated.
3) When you first add the salt to the organic layer it will clump together. You keep adding a drying agent until it disperses evenly when you swirl the flask.
4) Finally, you filter the mixture to remove the solid drying agent.

Question 48

How can you remove impurities from a product by washing it?

Answer 48

The product can be contaminated with leftover reagents or unwanted side products. You can remove some of these by washing the product.

Question 49

How can you purify volatile liquids?

Answer 49

1) connect a condenser to a round-bottomed flask containing your impure product in a solution.
2) Place a thermometer in the neck of the flask
3) Heat the impure product
4) When the product that you want to collect boils place a flask at the end of the condenser to collect the pure product.

Question 50

How can organic solids be purified by recrystallization?

Answer 50

1) Add a very hot solvent to the impure solid until it just dissolves. (saturated solution)
2) Filter the hot solution through a heated funnel to remove any insoluble impurities.
3) Leave the solution to cool down slowly. Crystals of the product will form as it cools/
4) Remove the liquid containing the soluble impurities from the crystals by filtering the mixture under reduced pressure (Buchner funnel)
5) Finally wash the crystals with an ice-cold solvent to remove any soluble impurities from their surface. then leave your purified crystals to dry.

Question 51

How can you guess how pure something is?

Answer 51

From its melting and boiling points. Pure substances have specific melting and boiling points while mixtures have a range.

Question 52

How can you measure the melting point of an organic substance?

Answer 52

1) You can use the melting and boiling point apparatus to accurately determine the melting point of an organic solid.
2) Pack a small sample of the solid into a glass capillary tube and place it inside the heating element.
3) Increase the temperature until the sample turns from solid to liquid.
4) You usually measure a melting range
5) You can look up the melting point of a substance in data books and compare it to your measurements.
6) Impurities in the sample will lower the melting point and broaden the melting range