3.3.7 Nomenclature, Isomerism and Compounds Containing Carbonyl Group (A2)

Question 1

What are Optical Isomers?

Answer 1

Mirror Images of Each Other

Type of Stereoisomerism (same structural formula, different shape)

Question 2

What is a Chiral (or Asymmetric) Carbon?

Answer 2

Carbon atom that has four different groups attached to it

Question 3

What are Enantiomers?

Answer 3

Mirror images, no matter which way they are turned, they can’t be superimposed

Question 4

How do Optical Isomers Rotate Plane-Polarised Light?

Answer 4

1) Normal light vibrates in all directions. Plane-Polarised Light vibrates in one direction
2) Optical isomers are optically active – rotate plane-polarised light
3) One enantiomer rotates it in clockwise direction, other rotates it in anti-clockwise direction

Question 5

What is a Racemic Mixture?

Answer 5

A Racemate (Racemic Mixture) contains equal quantities of each enantiomer of an optically active compound

Question 6

What types of reactions typically form Racemic mixtures?

Answer 6

Reactions involving Planar Bonds.
Double bonds (e.g. C=O and C=C) are planar (flat).
Products of reactions that happen at the carbonyl group of aldehydes and unsymmetrical ketones are often enantiomers present as a racemic mixture

Question 7

Where is the Carbonyl Group in an Aldehyde?

Answer 7

Carbonyl group is at the end of the carbon chain

All names end with -al

Question 8

Where is the Carbonyl Group in a Ketone?

Answer 8

Carbonyl group in the middle of the Carbon Chain

All names end with -one, often have a number to show which Carbon the carbonyl group is on

Question 9

What is a Carbonyl Functional Group In Aldehydes and Ketones?

Answer 9

1) R-C=O
        I
       H
2) R-C=O
         I
        R

Question 10

What is formed when an Aldehyde is Oxidised?

Answer 10

Carboxylic Acid

Question 11

Why is Tollens’ used to test for Aldehydes?

Answer 11

As Aldehyde is oxidised, Ag+ ions in Tollens’ are reduced to Ag atoms forming silver mirror
Nothing happens when mixed with a Ketone

Question 12

What happens when Fehling’s is mixed with an Aldehyde

Answer 12

Cu2+ ions reduced to brick-red ppt (Cu+)

Nothing happens with a Ketone

Question 13

How do you reduce Aldehydes and Ketones back to Alcohols?

Answer 13

NaBH4 (Sodium Tetrahydridoborate (III) or Sodium Borohydride) dissolved in water with Methanol is usually the reducing agent used.

Nucleophilic Addition Reaction. H- ion acts as a nucleophile and adds on to partially positive Carbon atom

Question 14

What type of reaction occurs when Potassium Cyanide is reacted with Carbonyls?

Answer 14

Nucleophilic Addition

Question 15

What do Carboxylic Acids contain?

Answer 15

-COOH (Carboxyl functional group)

To name them, find and name longest alkane chain, take off ‘e’ and add ‘-oic acid’

Question 16

Why are Carboxylic Acids weak acids?

Answer 16

They partially dissociate into a Carboxylate ion and an H+ ion in water

Question 17

What is formed when Carboxylic Acids react with Carbonates?

Answer 17

Carbon Dioxide

Question 18

What is formed when Carboxylic Acids react with Alcohols?

Answer 18

Esters
e.g.
Ethanoic Acid + Ethanol ⟶ Ethyl Ethanoate + Water (Ethyl from alcohol, Ethanoate from acid)

Question 19

What are Esters?

Answer 19

Organic Compounds that contain a -COO- functional group

Question 20

What are Esters used for?

Answer 20

Food Flavourings, Perfumes, Solvents and Plasticers

Question 21

Why are Esters used for what they are used for?

Answer 21

1) Esters have a sweet smell, varying from gluey sweet to fruity ‘pear drops’. Makes them useful for perfumes. Food industry uses esters to flavour things like drinks and sweets
2) Esters are polar liquids so lots of polar organic compounds dissolve in them. Also got quite low bps, so evaporate easily from mixtures. Makes good solvents in glues and printing inks
3) Used as Plasticisers – added to plastics during polymerisation to make plastic more flexible. Over time, plasticiser molecules escape and plastic becomes brittle and stiff

Question 22

How can Esters form Alcohols?

Answer 22

Can be Hydrolysed by Acid or Base Hydrolysis

Question 23

What does Acid Hydrolysis produce?

Answer 23

Dilute Acid and Alcohol
e.g.
Ethanoic Acid + Ethanol

Question 24

What does Base Hydrolysis produce?

Answer 24

Carboxylate ion and Alcohol
e.g.
Ethanoate + Ethanol

Question 25

What are Fats and Oils esters of?

Answer 25

Glycerol and Fatty Acids

Question 26

What are Fatty Acids?

Answer 26

Long chain carboxylic acids.

Combine with Glycerol (Propane-1,2,3-triol) to make esters

Question 27

What can Oils and Fats be hydrolysed into?

Answer 27

To make Glycerol, Soap and Fatty Acids

When Vegetable Oils and Animal Fats heated with NaOH, Glycerol and Sodium Salt (Soap) Produced

Question 28

What is Biodiesel?

Answer 28

Mixture of Methyl Esters of Fatty Acids

Question 29

How is Biodiesel produced?

Answer 29

1) Vegetable oils, e.g. Rapeseed oil, make good vehicle fuels but cannot be burned directly in engines
2) Oils must be converted into Biodiesel first. This involves reacting them with methanol, using potassium hydroxide as a catalyst
3) Get a mixture of methyl esters of fatty acids – Biodiesel

Question 30

What functional group does Acyl (or Acid) Chlorides have?

Answer 30

-COCl

All names end -oyl chloride

Question 31

What can Acyl Chlorides react with to lose Chlorine?

Answer 31

1) Water, vigorous reaction w/cold water produces Carboxylic Acid
2) Alcohols, vigorous reaction @ room temp. produces an ester
3) Ammonia, vigorous reaction @ room temp. produces an amide
4) Primary Amines, violent reaction @ room temp. produces an N-substituted amide
Each time Cl substituted with Oxygen or Nitrogen Group and Hydrogen Chloride fumes (HCl gas) given off

Question 32

How do Acyl Chlorides and Acid Anhydrides react?

Answer 32

Exactly the same, however, Carboxylic acid is produced instead of HCl gas.

Question 33

What types of reactions are Acyl Chloride Reactions?

Answer 33

Nucleophilic Addition-Elimination

Both Chlorine and Oxygen atoms draw electrons towards them, so carbon has slight positive charge

Question 34

Why is Ethanoic/Acetic Anhydride used for the manufacture of Aspirin instead of Ethanoyl Chloride?

Answer 34

1) Cheaper than Ethanoyl Chloride
2) Safer to use than Ethanoyl Chloride as its less corrosive, reacts more slowly with water, and doesn’t produce dangerous HCl fumes

Question 35

What is Step 1 of Separation of Water Soluble Impurities from a Water Insoluble Product?

Answer 35

Remove any impurities that dissolve in water

1) Once reaction completed, pour mixture into separating funnel and add water
2) Shake funnel and then allow to settle. Organic layer and aqueous layer are immiscible (don’t mix), so separate into 2 different layers
3) You can open tap and run each layer off into a separate container

Question 36

What is Step 2 of Separation of Water Soluble Impurities from a Water Insoluble Product?

Answer 36

Remove Water from Purified Product by Drying It:

1) Organic layer will end up containing trace amounts of water – has to be dried
2) Add an anhydrous salt (e.g. MgSO4 or CaCl2). Salt is used as drying agent – binds to any water present
3) When first added, it will clump together. Keep adding drying agent until it disperses evenly when you swirl the flask
4) Filter mixture to remove solid drying agent – use a piece of filter paper into a funnel that feeds into a flask and pour mixture into filter paper

Question 37

What is Step 3 of Separation of Water Soluble Impurities from a Water Insoluble Product?

Answer 37

Remove Other Impurities by Washing:

1) Product of reaction can be contaminated w/leftover reagents or unwanted side products.
2) Remove some of these by washing the product (adding another liquid and shaking)
3) e.g. Sodium Hydrogencarbonate can be added to an impure product in solution to remove acid from it. Acid reacts with Sodium Hydrogencarbonate to give CO2 gas and the organic product can be removed using a separating funnel.

Question 38

How can Volatile Liquids be Purified?

Answer 38

By Distillation:

1) Connect condenser to a round bottomed flask containing impure product in solution
2) Place thermometer in neck of flask so that bulb sits next to the entrance to the condenser. Temp of thermometer will show boiling point of substance that’s evaporating at any given time
3) Heat the impure product (many are flammable so use electric heater instead of bunsen burner)
4) When the product you want to collect boils (i.e. when thermometer shows its boiling point), place a flask at open end of the condenser to collect pure product

Question 39

How can Organic Solids be Purified?

Answer 39

By Recrystallisation:

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

Question 40

Why are melting and boiling points a good indicator of purity?

Answer 40

Pure substances have a specific mp and bp. If impure, mp’s lowered and bp is raised

1) Use melting point apparatus to accurately determine mp of organic solid
2) Pack small sample of solid into glass capillary tube and place inside heating element
3) Increase temp until sample turns from solid to liquid
4) Usually measure a melting range, which is range of temps from where solid begins to melt to where it has completely melted
5) Look up melting point of substance in data books and compare it to measurements
6) Impurities in sample will lower mp and broaden melting range