CIE AS Chemistry (9701) 2019-2021

Revision Notes

3.1.3 Deducing Isomers of a Compound

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
  • Stereo
    • Geometric? No, as the compound can’t be an unsaturated or cyclic compound with molecular formula C4H10
    • Optical? No, as there are no chiral centres
  • Structural
    • 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

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