Planning 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 A Level Chemistry)

Revision Note

Aliphatic Reaction Pathways

Aromatic Reaction Pathways

Designing a Reaction Pathway

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1. Physical Chemistry

1.1 Atomic Structure

1.1.1 Structure of the Atom

1.1.2 Isotopes

1.1.3 Relative Mass

1.1.4 Mass Spectrometry

1.2 Ions & Electrons

1.2.1 Ionisation Energy

1.2.2 Quantum Shells

1.2.3 Orbitals

1.2.4 Electronic Configurations

1.3 The Periodic Table

1.3.1 Periodicity

1.4 Bonding

1.4.1 Ionic Bonding Overview

1.4.2 Representing Ionic Bonding

1.4.3 Ionic Trends

1.4.4 Physical Properties of Ionic Compounds

1.4.5 Covalent Bonding Overview

1.4.6 Covalent Dot-and-Cross Diagrams

1.4.7 Bond Length & Bond Strength

1.4.8 Shapes of Covalent Compounds

1.5 Structure

1.5.1 Electronegativity

1.5.2 Intermolecular Forces

1.5.3 Hydrogen Bonding

1.5.4 Intermolecular Forces & Physical Properties

1.5.5 Metallic Bonding

1.5.6 Giant Lattices

1.5.7 Covalent Structures

1.5.8 Predicting Structures

1.6 Formulae, Equations & Avogadro

1.6.1 Empirical & Molecular Formulae

1.6.2 Balanced Equations

1.6.3 Applying Equations

1.6.4 The Mole & the Avogadro Constant

1.6.5 Amount of Substance Calculations

1.7 Reaction Calculations

1.7.1 Reacting Volume Calculations

1.7.2 Titrations

1.7.3 Error & Uncertainty

1.7.4 Yield & Atom Economy

1.8 Energetics I

1.8.1 Enthalpy Changes

1.8.2 Enthalpy Level Diagrams

1.8.3 Calorimetry

1.8.4 Hess Cycles

1.8.5 Bond Enthalpy

1.9 Kinetics I

1.9.1 Collision Theory & Rates

1.9.2 Calculating Rates of Reaction

1.9.3 Maxwell-Boltzmann Distributions

1.9.4 Catalysts in Industry

1.10 Equilibrium I

1.10.1 Dynamic Equilibrium

1.10.2 Le Chatelier's Principle

1.10.3 The Rate & Yield Compromise

1.10.4 Deducing Kc Expressions

2. Inorganic Chemistry

2.1 Redox I

2.1.1 Oxidation Number

2.1.2 Types of Reduction & Oxidation

2.1.3 Redox & Disproportionation

2.1.4 Ionic Equations

2.2 Groups 1 & 2

2.2.1 Explaining Group 2 Trends

2.2.2 Reactions of Group 2

2.2.3 Group 2 Hydroxides & Sulfates

2.2.4 Group 1 & 2 Carbonates & Nitrates

2.2.5 Flame Tests

2.3 Group 7

2.3.1 Group 7 Trends