Isomerism is one of the most important fundamentals that all A-Level H2 Chemistry students must be very good with, in order to solve application-type organic chemistry questions later on.
Isomerism occurs when two or more compounds have the same molecular formula but different arrangement of the atoms in the molecules.
Isomers may have vastly different physical and chemical properties depending on the structure and functional groups present. These properties may affect the way the compounds are used in chemistry laboratories and the industry.
There are two main types of isomerism:
A) Structural Isomerism: atoms are linked together in different ways
- Chain Isomerism: different skeletal chain i.e. straight chain vs branching
- Positional Isomerism: different positions of the same functional group
- Functional Group Isomerism: different functional groups e.g. aldehyde vs ketone, carboxylic acids vs esters
Note that Structural Isomerism is also commonly known as Constitutional Isomerism.
B) Stereoisomerism: atoms have different spatial arrangements
- Geometric Isomerism: caused by restriction of rotation of a covalent bond due to double bonds or certain ring systems
- Optical Isomerism: present in molecules that can exist as two non-superimposable mirror images
Note that Geometric Isomerism is also commonly known as Cis-Trans Isomerism.
Note that Optical Isomerism is also commonly known as Enantiomerism.
The flow-chart below will give you a good idea on the differences and similarities when it comes to the different types of isomerism in organic chemistry.
The discussion above is all based on A-Level H2 Chemistry which follows the Cambridge International Examination’s syllabus (new syllabus code 9729).
I hope you find the content easy for your understanding and if you have any questions, leave me a comment below. Feel free to share this blog post with your friends and learn the key H2 Organic Chemistry concepts together.
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