Home

Chemistry

Amines and polymers

Optical isomers and chirality

Select Lesson

Exam Board

Select an option

Practical skills

The scientific method

How to plan experiments

Improving repeatability and reproducibility

Presenting results using tables and graphs

Analysing results: anomalies and correlation

Evaluating experiments

Organic synthesis and analysis

Synthetic routes

NMR spectroscopy

Proton NMR spectroscopy

Chromatography

Amino acids, proteins and DNA

Amino acids and zwitterions

Amino acids, proteins and enzymes

DNA structure and cis-platin

Aromatic chemistry, amines and polymers

Benzene: structure and combustion

Electrophilic substitution

Friedel-Crafts reactions

Aliphatic and aromatic amines

Reactions of amines

Forming amides

Condensation polymers

Polymer disposal

Isomerism and carbonyls

Optical isomers and chirality

Aldehydes and ketones

Carboxylic acids: properties and reactions

Esters: formation, properties and uses

Acyl chlorides: formation and reactions

Transition metals

Transition metals: electron configuration and oxidation number

Complex ions: formation, shape and isomerism

Colours of inorganic ions and complexes

Ligand substitution reactions

Redox titrations

Transition metals as catalysts

Metal-aqua ions

Period 3 elements

Period 3 elements and oxides

Acids and bases

pH calculations

The ionic product of water

pH curves and indicators

Titration calculations

Buffer solutions and calculations

Electrode potentials and cells

Electrochemical cells and redox

Electrode potentials and calculations

The electrochemical series

Energy storage cells and hydrogen fuel cells

Rate equations

Measuring rates of reaction

Rate equations and the rate constant

Determining reaction orders

The initial rates method

The rate determining step

Activation energy and the Arrhenius equation

Partial pressure and gas equilibria

Le Chatelier's principle and equilibrium constants

Thermodynamics

Lattice enthalpies and Born-Haber cycles

Polarisation and the Pauling scale

Enthalpy change in solution

Entropy and calculating entropy change

Gibbs free energy change

Organic analysis

Testing for functional groups

Mass spectrometry

IR spectroscopy

Alkenes and alcohols

Alkenes: bonding and reactivity

Reactions of alkenes

Addition polymerisation

Alcohol: classification and reactions

Oxidation of alcohols

Ethanol production

Alkanes and halogenoalkanes

Alkanes and free radical substitution

Fractional distillation of crude oil

Fuels: combustion and emissions

Haloalkanes and the environment

Halogenoalkanes and their reactions

Organic chemistry - the basics

Basic concepts of organic chemistry

Organic reactions and mechanisms

Structural isomerism

Stereoisomerism

Group 2 and 7 elements

Group 2: ionisation energy and properties

Chemical properties of Group 7

Reactions with halogens

Halide ion reactions

Testing for ions

Kinetics, equilibria and redox

Collision theory and rates of reaction

Calculating the rate of reaction

Catalysts and the Maxwell-Boltzmann distribution

Reversible reactions

Le Chatelier's principle

The equilibrium constant

Calculating oxidation numbers

Oxidation, reduction and redox reactions

Energetics

Enthalpy changes and reaction profiles

Standard enthalpy changes

Calculating bond enthalpies

Hess's Law and enthalpy cycles

Bonding

Ionic bonding

Covalent bonding

Shapes of molecules

Giant covalent and metallic structures

Predicting structures and properties

Electronegativity and polarisation

Intermolecular forces: types and examples

Hydrogen bonding

Amount of substance

The mole and Avogadro's constant

Calculations involving gases

Balancing equations

Acid-base titrations

Empirical and molecular formulae

Atom economy and percentage yield

Atomic structure

The atom: history, structure and isotopes

Relative masses and mass spectrometry

Electronic structure: shells and orbitals

Ionisation energies

Ionisation energy trends

Periodicity

Explainer Video

Tutor: Alisha

Summary

Optical isomers and chirality

In a nutshell

Optical isomers are a type of stereoisomer. They contain a chiral centre and they rotate plane-polarised light.

Properties of optical isomers

Optical isomers are a type of stereoisomer. Some of their defining properties are:

They have a chiral centre - an atom with four different atoms or group of atoms attached to it.
They are mirror images of each other - they cannot be superimposed.
They are optically active - they rotate plane polarised light.
They are also known as enantiomers.

Optically active

As optical isomers are optically active they rotate plane-polarised light. This means that light vibrates in one direction, unlike normal light which vibrates in all directions. One enantiomer rotates in the clockwise direction, whilst the other rotates in an anti-clockwise direction.

Racemate

A racemate is a mixture of enantiomers in equal amounts. Racemates do not display optical activity because the enantiomers cancel the light rotating effect of each other.

Reaction products of planar molecules give rise to a racemate. The planar molecules must be unsymmetrical for a racemic mixture to arise. A symmetrical planar molecule will not display optical isomerism.

Example

Chemistry; Organic chemistry II; KS5 Year 12; Optical isomers and chirality

Drawing optical isomers

procedure

1.	Identify the chiral centre.
2.	Draw one of the enantiomers in a tetrahedral shape.
3.	Draw the mirror image next to it.
4.	Draw a dashed line in-between the two enantiomers.

Multiple chiral centres

Some molecules have more than one chiral centres. Molecules with more than one chiral centre will have more than two optical isomers. The maximum number of optical isomers can be found by using the formula:

$Total \,number\, of \,optical\, isomers = 2^n \\where \,n \,is\,the \,number \,of\,chiral\,centres$

Example

Determine the total number of isomers for $2$ -methylpentan- $4$ -ol.

Firstly, find the number of chiral centres. For this example:

$n = 2$

Then, use the number of chiral centres to find the total number of optical isomers:

$Total \,number\, of \,optical\, isomers = 2^n = 2^2 = \underline4$

The diagram below displays all the optical isomers for $2$ -methylpentan- $4$ -ol.

Learn with Basics

Length:

Unit 1

Organic reactions and mechanisms

Unit 2

Basic concepts of organic chemistry

Jump Ahead

Optional

Unit 3