Isomerism

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Structural Isomerism

Structural isomers are molecules which have the same molecular formula but a different arrangement of atoms in space.

Chain isomers

Chain isomers are molecules that have the same molecular formula but one is linear and one is branched. For example:
- Butane is a linear molecule with the molecular formula C₄H₁₀.
- Methylpropane is a branched molecule with the molecular formula C₄H₁₀.

Position isomers

Position isomers are molecules that have the same molecular formula but have their functional group in different places. For example:
- Butan-1-ol has a hydroxyl group attached to carbon-1.
- Butan-2-ol has a hydroxyl group attached to carbon-2.

Functional group isomers

Functional group isomers are isomers that have had their structures changed so that they have different functional groups. For example:
- Propanoic acid.
- Methyl ethanoate.

Stereoisomerism

Stereoisomers are molecules that have the same molecular formula, same functional groups and same functional group positions but different arrangements of atoms in space.

Alkene stereoisomerism

Stereoisomerism can be seen in alkenes.
It is possible in alkenes because of the presence of double bonds:
- Unlike single bonds, double bonds are rigid and you cannot rotate around them.
- So alkenes can display stereoisomerism at the double bond.

An example

The simplest way to understand what this means is with an example.
- Above are the two different alkenes, (E)-but-2-ene and (Z)-but-2-ene.
  - The molecules are the same in every way, except for the atoms' position in space.

What do E and Z mean?

E and Z come from the German words 'entgegen' and 'zusammen' for 'opposite' and 'together'.
- An E-alkene has the larger groups on opposite sides.
- A Z-alkene has the larger groups on the same side.
A good way to remember this is that Z alkenes have large groups on the 'zame zide'.

Cahn-Ingold Prelog Rules

The Cahn-Ingold Prelog rules help us assign E/Z isomerism to more complicated molecules.

The Cahn-Ingold Prelog rules

They help to distinguish between E and Z isomers for more complicated cases.
The rules work by numbering the four directly connecting atoms in order of their atomic mass number. From this, we give them a 'priority'.
- The highest atomic number gets priority 1.
- The second highest atomic number gets priority 2, and so on.

E vs Z

E:
- Priority 1 and 2 are on different sides of the double bond.
  - I.e. The two atoms with the highest atomic mass number are on different sides.
Z:
- Priority 1 and 2 are on the same side of the double bond.
  - I.e. The two atoms with the highest atomic mass number are on the same side.

An example: E

The shown but-2-ene is an E geometry because the two methyl groups are on opposite sides of the double bond.

An example: Z

The shown but-2-ene is a Z geometry because the two methyl groups are on the same side of the double bond.

1Physical Chemistry

1.1Atomic Structure

1.1.1Fundamental Particles

1.1.2Isotopes & Mass Number

1.1.3Mass Spectrometry

1.1.4Electron Shells, Sub-Shells & Orbitals

1.1.5Electron Configuration

1.1.6Ionisation Energy

1.1.7Factors Affecting Ionisation Energies

1.1.8Trends of Ionisation

1.1.9Specific Impacts on Ionisation Energies

1.1.10End of Topic Test - Atomic Structure

1.1.11A-A* (AO3/4) - Atomic Structure

1.2Amount of Substance

1.2.1Relative Masses

1.2.2The Mole

1.2.3The Ideal Gas Equation

1.2.4Empirical & Molecular Formulae

1.2.5Balanced Equations

1.2.6Percentage Yield

1.2.7A-A* (AO3/4) - Percentage Yield

1.2.8Atom Economy

1.2.9End of Topic Test - Amount of Substance

1.2.10A-A* (AO3/4) - Substances & Yield

1.3Bonding

1.3.1Ionic Bonding

1.3.2Covalent & Dative Bonding

1.3.3Carbon Structures

1.3.4Metallic Bonding

1.3.5Physical Properties

1.3.6Shapes of Molecules

1.3.7Polarity

1.3.8Intermolecular Forces

1.3.9Intermolecular Forces 2

1.3.10End of Topic Test - Bonding

1.3.11Exam-Style Question - Shape of Molecules

1.3.12A-A* (AO3/4) - Bonding

1.4Energetics

1.4.1Enthalpy Changes

1.4.2Calorimetry

1.4.3Hess' Law

1.4.4Bond Enthalpies

1.4.5End of Topic Test - Energetics

1.5Kinetics

1.5.1Collision Theory

1.5.2Maxwell-Boltzmann Distribution

1.5.3Increasing Rates

1.5.4End of Topic Test - Kinetics

1.6Equilibria

1.6.1Le Chatelier

1.6.2Equilibrium Constants

1.6.3A-A* (AO3/4) - Energetics, Kinetics, Equilibria

1.6.4End of Topic Test - Equilibria

1.7Redox

1.7.1Redox

1.7.2End of Topic Test - Redox

2Physical Chemistry 2 (A2 Only)

2.1Thermodynamics (A2 Only)

2.1.1Born-Haber Cycles (A2 Only)

2.1.2Born-Haber Cycle Calculations (A2 Only)

2.1.3Entropy (A2 Only)

2.1.4Free Energy (A2 Only)

2.1.5End of Topic Test - Thermodynamics

2.1.6A-A* (AO3/4) - Thermodynamics

2.2Rate Equations (A2 Only)

2.2.1Rate Equations (A2 Only)

2.2.2Rate Equations 2 (A2 Only)

2.2.3The Arrhenius Equation (A2 Only)

2.2.4Experimental Methods for Rates (A2 Only)

2.2.5End of Topic Test - Rate Equations

2.2.6Exam-Style Question - Rates

2.2.7A-A* (AO3/4) - Rate Equations

2.3The Equilibrium Constant Kp (A2 Only)

2.3.1Properties of Kp (A2 Only)

2.4Electrochemical Cells (A2 Only)

2.4.1Electrochemical Cells (A2 Only)

2.4.2Electrochemical Series (A2 Only)

2.4.3Commercial Application (A2 Only)

2.4.4End of Topic Test - Kp & Electrochemistry

2.4.5A-A* (AO3/4) - Electrochemical Cells

2.5Acids & Bases (A2 Only)

2.5.1Brønsted-Lowry Acids & Bases (A2 Only)

2.5.2pH (A2 Only)

2.5.3The Ionic Product of Water (A2 Only)

2.5.4Weak Acids & Bases (A2 Only)

2.5.5pH Curves & Titrations (A2 Only)

2.5.6pH Curves & Titrations 2 (A2 Only)

2.5.7Buffer Solutions (A2 Only)

2.5.8End of Topic Test - Acids & Bases

2.5.9Exam-Style Question - Weak Acids

2.5.10A-A* (AO3/4) - Acids & Bases

3Inorganic Chemistry

3.1Periodicity & Trends

3.1.1The Periodic Table

3.1.2Trends in the Periodic Table

3.1.3End of Topic Test - Periodicity & Trends

3.2Group 2

3.2.1Group 2 Chemistry

3.2.2End of Topic Test - Group 2

3.3Group 7

3.3.1Introduction to Halogens

3.3.2Reactions of Halogens

3.3.3Chlorine & Chlorate(I)

3.3.4End of Topic Test - Group 7

3.3.5Exam-Style Question - Group 7

3.3.6A-A* (AO3/4) - Periodicity, Group 2 & 7

4Inorganic Chemistry 2 (A2 Only)

4.1Period 3 (A2 Only)

4.1.1Period 3 Elements & Oxides (A2 Only)

4.1.2Period 3 Oxides (A2 Only)

4.1.3End of Topic Test - Period 3

4.2Transition Metals (A2 Only)

4.2.1General Properties (A2 Only)

4.2.2Substitution Reactions (A2 Only)

4.2.3Shapes of Complex Ions (A2 Only)

4.2.4Colours of Ions (A2 Only)

4.2.5Variable Oxidation States (A2 Only)

4.2.6Titrations (A2 Only)

4.2.7Homogeneous Catalysts (A2 Only)

4.2.8Heterogeneous Catalysts (A2 Only)

4.2.9End of Topic Test - Transition Metals

4.2.10A-A* (AO3/4) - Transition Metals

4.3Reactions of Ions in Aqueous Solutions (A2 Only)

4.3.1Acidity (A2 Only)

4.3.2Identification (A2 Only)

4.3.3End of Topic Test - Reactions of Ions in Solution

5Organic Chemistry 1

5.1Introduction

5.1.1Naming Conventions

5.1.2Mechanism

5.1.3Isomerism

5.1.4End of Topic Test - Introduction to Organic Chem

5.2Alkanes

5.2.1Fractional Distillation

5.2.2Cracking

5.2.3Combustion

5.2.4Chlorination

5.2.5End of Topic Test - Alkanes

5.3Halogenoalkanes

5.3.1Substitution Reactions

5.3.2Elimination Reactions

5.3.3Ozone Depletion

5.3.4End of Topic Test - Halogenoalkanes

5.4Alkenes

5.4.1Introduction to Alkenes

5.4.2Reactions of Alkenes

5.4.3Polymerisation Reactions

5.4.4Properties of Polymers

5.4.5End of Topic Test - Alkenes

5.5Alcohols

5.5.1Production of Alcohols

5.5.2Oxidation of Alcohols

5.5.3Oxidation of Alcohols - 2

5.5.4Elimination Reactions

5.5.5End of Topic Test - Alcohols

5.5.6Exam-Style Question - Alcohols

5.6Organic Analysis

5.6.1Reactions

5.6.2Reactions 2

5.6.3Mass Spectrometry

5.6.4Infrared Spectroscopy

5.6.5End of Topic Test - Organic Analysis

5.7A-A* (AO3/4) - Organic 1

5.7.1A-A* (AO3/4) - Organic 1

6Organic Chemistry 2 (A2 Only)

6.1Optical Isomerism (A2 Only)

6.1.1Optical Isomerism (A2 Only)

6.1.2End of Topic Test - Optical Isomerism

6.2Aldehydes & Ketones (A2 Only)

6.2.1Aldehydes & Ketones (A2 Only)

6.2.2End of Topic Test - Aldehydes & Ketones

6.3Carboxylic Acids & Esters (A2 Only)

6.3.1Acids & Esters (A2 Only)

6.3.2Acylation (A2 Only)

6.3.3End of Topic Test - Carboxylic Acids & Esters

6.4Aromatic Chemistry (A2 Only)

6.4.1Structure & Reactivity (A2 Only)

6.4.2Reactions of Benzene (A2 Only)

6.4.3End of Topic Test - Aromatic Chemistry

6.5Amines (A2 Only)

6.5.1Nature & Preparation of Amines (A2 Only)

6.5.2Basicity & Nucleophilicity (A2 Only)

6.5.3End of Topic Test - Amines

6.6Polymers (A2 Only)

6.6.1Condensation Polymers (A2 Only)

6.6.2Biodegradability (A2 Only)

6.7Biological Organic (A2 Only)

6.7.1Amino Acids (A2 Only)

6.7.2Proteins (A2 Only)

6.7.3DNA (A2 Only)

6.7.4Anti-Cancer Drugs (A2 Only)

6.7.5End of Topic Test - Biological Organic

6.8Organic Synthesis (A2 Only)

6.8.1Organic Synthesis (A2 Only)

6.8.2Examples of Synthetic Routes (A2 Only)

6.8.3End of Topic Test - Polymers & Organic Synthesis

6.9NMR Spectroscopy (A2 Only)

6.9.1Understanding NMR (A2 Only)

6.9.2Carbon-13 NMR (A2 Only)

6.9.3Hydrogen-1 NMR (A2 Only)

6.9.4Hydrogen-1 NMR 2 (A2 Only)

6.9.5End of Topic Test - NMR

6.10Chromatography (A2 Only)

6.10.1Overview of Chromatography (A2 Only)

6.10.2Thin-Layer Chromatography (A2 Only)

6.10.3Column Chromatography (A2 Only)

6.10.4Gas Chromatography (A2 Only)

6.10.5End of Topic Test - Chromatography

6.11A-A* (AO3/4) - Organic 2

6.11.1A-A* (AO3/4) - Organic 2

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