Planning Reaction Schemes | Edexcel International A Level Chemistry Revision Notes 2017

Reaction Schemes

A large number of organic products are made from a few starting compounds using appropriate reagents and conditions
Knowing how organic functional groups are related to each other is key to the synthesis of a given molecule
The main functional groups you need to know are
- Alkanes
- Alkenes
- Haloalkanes
- Nitriles
- Amines
- Alcohols
- Carbonyls (aldehydes & ketones)
- Hydroxynitriles
- Carboxylic acids
- Esters
- Acyl chlorides
- Primary and secondary amides

Aliphatic Reaction Pathways

The key interconversions between functional groups are summarised here:

Aliphatic Reactions Table

Reactant	Product	Reagents	Reaction
Alkene	Haloalkane	X₂ / HX	Electrophilic addition
Alkene	Alcohol	Steam + H₂SO₄/ heat	Hydration
Alkene	Alkane	Hydrogen + Ni catalyst / 150 ^oC	Electrophilic addition / hydrogenation
Alcohol	Alkene	Al₂O₃ or conc. H₂SO₄/ heat	Elimination / dehydration
Alcohol	Haloalkane	NaX + H₂SO₄/ reflux	Nucleophilic substitution
Haloalkane	Alcohol	NaOH (aq) / reflux	Nucleophilic substitution
Alkane	Haloalkane	Halogen / UV light	Free radical substitution
Primary alcohol	Aldehyde	K₂Cr₂O₇ / H₂SO₄/ distil	Oxidation
Secondary alcohol	Ketone	K₂Cr₂O₇ / H₂SO₄/ Heat	Oxidation
Primary alcohol	Carboxylic acid	K₂Cr₂O₇ / H₂SO₄/ reflux	Oxidation
Aldehyde	Primary alcohol	NaBH₄ / H₂O	Reduction / nucleophilic addition
Ketone	Secondary alcohol	NaBH₄ / H₂O	Reduction / nucleophilic addition
Haloalkane	Nitrile	Aqueous ethanolic KCN / Heat	Nucleophilic substitution
Halogenoalkane	Amine	NH₃ / ethanol	Nucleophilic substitution
Nitrile	Carboxylic acid	H₂O / HCl	Hydrolysis
Aldehyde	Hydroxynitrile	NaCN / H⁺	Nuclophilic addition
Alcohol	Ester	Carboxylic acid / H₂SO₄	Esterification
Carboxylic acid	Ester	Alcohol / H₂SO₄	Esterification
Ester	Carboxylate salt and alcohol	NaOH (aq)	Alkaline hydrolysis
Ester	Carboxylic acid	Dilute acid	Acid hydrolysis
Carboxylic acid	Acyl chloride	SOCl₂	Chlorination
Acyl chloride	Carboxylic acid	H₂O	Hydrolysis
Acyl chloride	Primary amide	NH₃	Nucleophilic addition elimination
Acyl chloride	Secondary amide	Primary amine	Nucleophilic addition elimination

Aromatic Reaction Pathways

The key aromatic reactions are summarised here:

Aromatic Reactions Table

Reactant	Product	Reagents	Reaction
Benzene	Methylbenzene / toluene	CH₃Cl / AlCl₃	Alkylation / Electrophilic substitution
Benzene	Bromobenzene	Br₂ / FeBr₃	Bromination / Electrophilic substitution
Benzene	Chlorobenzene	Cl₂ / AlCl₃	Chlorination / Electrophilic substitution
Benzene	Nitrobenzene	HNO₃ / H₂SO₄	Nitration / Electrophilic substitution
Nitrobenzene	Aminobenzene / phenylamine / aniline	Sn / HCl	Reduction
Aminobenzene	2,4,6-tribromoaminobenzene / 2,4,6-tribromoaniline	Bromine	Electrophilic substitution
Benzene	Phenylethanone	CH₃COCl / AlCl₃	Acylation / Electrophilic substitution
Phenylethanone	1-phenylethanol	NaBH₄	Reduction

Designing a Reaction Pathway

The given molecule is usually called the target molecule and chemists try to design a synthesis as efficiently as possible
Designing a reaction pathway starts by drawing the structures of the target molecule and the starting molecule
Determine if they have the same number of carbon atoms
- If you need to lengthen the carbon chain you will need to put on a nitrile group by nucleophilic substitution
Work out all the compounds that can be made from the starting molecule and all the molecules that can be made into the target molecule
- Match the groups they have in common and work out the reagents and conditions needed

Worked example

Suggest how the following syntheses could be carried out:

a) Chloroethane to ethanoic acid

b) Ethene to 1-aminopropane

Answer 1

Organic synthesis WE Answer 1, downloadable AS & A Level Chemistry revision notes

Answer 2

Organic synthesis WE Answer 2, downloadable AS & A Level Chemistry revision notes

Examiner Tip

You could be required to design a synthesis with up to four steps

Part of this process can include identifying appropriate control measures to reduce risk, based on data about hazards

Planning Reaction Schemes (Edexcel International A Level Chemistry)

Revision Note

Aliphatic Reaction Pathways

Aromatic Reaction Pathways

Designing a Reaction Pathway

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1. Structure, Bonding & Introduction to Organic Chemistry

1.1 Formulae & Equations

1.1.1 Formulae & Mass

1.1.2 Avogadro & the Mole

1.1.3 Full & Ionic Equations

1.1.4 Calculating Formulae

1.2 Amount of Substance

1.2.1 Concentration Calculations

1.2.2 Reacting Mass Calculations

1.2.3 Reacting Volume Calculations

1.2.4 Calculations of Product

1.3 Atomic Structure

1.3.1 Sub-Atomic Particles

1.3.2 Isotopes & Mass Spectra

1.4 Electrons & Ions

1.4.1 Endothermic Ionisation Energy

1.4.2 Electronic Structures

1.4.3 Shapes of Orbitals

1.4.4 Electronic Configurations & Chemical Properties

1.5 The Periodic Table

1.5.1 Periodicity - Ionisation Energy

1.5.2 Periodicity - Thermal Trends

1.6 Ionic & Metallic Bonding & Structure

1.6.1 Evidence of Ions

1.6.2 Ionic Bonding & Structures

1.6.3 Ionic Bond Strength

1.6.4 Polarisation

1.6.5 Metallic Bonding & Lattices

1.7 Covalent Bonding & Structure

1.7.1 Evidence of Covalent Bonding

1.7.2 Covalent Bonding

1.7.3 Carbon Allotropes

1.7.4 Electronegativity

1.7.5 VSEPR Theory

1.7.6 Predicting Shapes & Angles

1.8 Introductory Organic Chemistry

1.8.1 Hazards & Risks

1.8.2 Functional Groups & Homologous Series

1.8.3 Nomenclature & Classification

1.8.4 Isomers - Structural

1.9 Alkanes

1.9.1 Alkanes - Introduction

1.9.2 Alkanes as Fuels

1.9.3 Combustion of Alkanes

1.9.4 Alternative Fuels

1.9.5 Free Radicals & Fission

1.9.6 The Free Radical Substitution Mechanism

1.10 Alkenes

1.10.1 Alkenes - Introduction

1.10.2 Isomers - Geometric

1.10.3 Reactions of Alkenes

1.10.4 Saturation Test

1.10.5 Electrophilic Addition - Mechanism

1.10.6 Addition Polymerisation

1.10.7 Polymer Disposal

2. Energetics, Group Chemistry, Halogenoalkanes & Alcohols

2.1 Energetics

2.1.1 Enthalpy Level Diagrams

2.1.2 Enthalpy Change - Definitions

2.1.3 Using Calorimetry

2.1.4 Using Hess Cycles

2.1.5 Bond Enthalpies

2.2 Intermolecular Forces

2.2.1 Intermolecular Forces - Introduction

2.2.2 Hydrogen Bonding

2.2.3 Physical Properties

2.2.4 Solvent Choice

2.3 Redox Chemistry & Acid-Base Titrations

2.3.1 Oxidation Numbers - Introduction

2.3.2 Oxidation & Reduction

2.3.3 Disproportionation Reactions

2.3.4 Ionic Equations