3.3.1.3 Isomerism Flashcards
Students should be able to: define the term structural isomer draw the structures of chain, position and functional group isomers define the term stereoisomer draw the structural formulas of E and Z isomers apply the CIP priority rules to E and Z isomers.
What is an Isomer?
Molecules that have the same molecular formula, but have a different arrangement of the atoms in space
If two separate molecules with the same molecular formula have been rotated / rotate around particular bonds, are they isomers of one another?
No
What is structural isomerism?
Atoms are arranged in completely different orders
What are the three types of structural isomerism?
- Chain
- Position
- Functional
Define Chain Isomerism
Isomers that have the capacity for carbons to branch
Define Position Isomerism
The basic carbon skeleton remains unchanged BUT important groups are moved around on the skeleton
Should you mix Chain and Position Isomerism when asked to draw Isomers in exams?
Yes
What is Functional Group Isomerism?
Isomers that contain different functional groups. They belong to different homologous series
After Functional Group Isomerism what will Alcohols become?
Ethers
What will Aldehydes become?
Ketones
What will Acids become?
Ethers
What will 1’amines become?
2’ (or 3’)
What is Stereoisomerism?
The atoms making up the isomers are joined up in the same order but still manage to have a different spatial arrangement
Is Stereoisomerism a form of Geometric isomerism?
No– vice versa
How does Geometric isomerism arise?
Occurs when there is restricted rotation within a molecule- so could never happen in alkanes for example
How can you make sure Geometric isomerism has occurred as opposed to rotation of the molecule?
Two different groups on the left-hand end of the bond and Two different groups on the right-hand end. It doesn’t matter whether the left-hand groups are the same as the right-hand ones or not.
How should structural formulae including double bonds be drawn?
Double bond should have correct bond degree angles– 120º– to easily identify CIS & TRANS geometric isomers
What is a CIS Geometric isomer?
Two atoms of the functional group are locked on the same side of the isomer
What is a TRANS Geometric isomer?
Two atoms of the same functional group are locked on opposite sides of the double bond
Compare the B.P. & M.P of CIS & TRANS geometric isomers
CIS: >BP
TRANS: >MP
