CIE AS Chemistry (9701) exams from 2022

Revision Notes

3.1.13 Isomers of Organic Compounds

Deducing Isomers of a Compound

  • You should be able to deduce all possible isomers for organic compounds knowing their molecular formula

Worked example: Isomers of dibromopropane

An Introduction to AS Level Organic Chemistry Worked Example - Isomers of dibromopropane, downloadable AS & A Level Chemistry revision notes

  • Step 1: Draw the structural formula of the compound

 

An Introduction to AS Level Organic Chemistry Step 1 Isomers of dibromopropane, downloadable AS & A Level Chemistry revision notes

 

  • Step 2: Determine whether it is a stereo or structural isomer
    There is no restricted bond rotation around the C-C bond and there is no chiral centre so it is structural isomerism
  • Step 3: Determine whether it is a functional group, chain or positional isomerism
    • Functional group? No, as Br is the only functional group possible
    • Chain? No, as the longest chain can only be 3
    • Positional? Yes, as the two bromine atoms can be bonded to different carbon atoms

 

An Introduction to AS Level Organic Chemistry Step 3 Isomers of dibromopropane, downloadable AS & A Level Chemistry revision notes

An Introduction to AS Level Organic Chemistry Answer Isomers of dibromopropane, downloadable AS & A Level Chemistry revision notes

Worked example: Deducing isomers of C4H10

An Introduction to AS Level Organic Chemistry Worked example - Deducing isomers of C4H10, downloadable AS & A Level Chemistry revision notes

  • Step 1: Draw the structural formula of the compound

 

An Introduction to AS Level Organic Chemistry Step 1 Deducing isomers of C4H10, downloadable AS & A Level Chemistry revision notes

  • Step 2: Determine whether it is a stereo or structural isomer.
    There is no restricted bond rotation around the C-C bond and there is no chiral centre so it is structural isomerism
  • Step 3: Determine whether it is a functional group, chain or positional isomerism
    • Functional group? No, as there are no functional groups
    • Positional? No, as there are no functional groups which can be positioned on different carbon atoms
    • Chain? yes!

 

An Introduction to AS Level Organic Chemistry Answer Deducing isomers of C4H10, downloadable AS & A Level Chemistry revision notes

Worked example: Deducing isomers of C2H2Cl2

An Introduction to AS Level Organic Chemistry Worked example - Deducing isomers of C2H2Cl2, downloadable AS & A Level Chemistry revision notes

  • Step 1: Draw the possible structural formula of the compound

 

An Introduction to AS Level Organic Chemistry Step 1 Deducing isomers of C2H2Cl2, downloadable AS & A Level Chemistry revision notes

  • Step 2: Determine whether it is a stereo or structural isomer
    The compound has to be unsaturated for it to have molecular formula C2H2Cl2 ; Due to the double bond there is restricted rotation about the C-C bond; This compound will therefore display geometrical isomerism
  • Step 3: Determine whether it is optical or geometrical isomerism
    • Optical? No, as there are no chiral centres
    • Geometric? Yes!

  

An Introduction to AS Level Organic Chemistry Answer Deducing isomers of C2H2Cl2, downloadable AS & A Level Chemistry revision notes

Author: Francesca

Fran has taught A level Chemistry in the UK for over 10 years. As head of science, she used her passion for education to drive improvement for staff and students, supporting them to achieve their full potential. Fran has also co-written science textbooks and worked as an examiner for UK exam boards.
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