13.2 Steroisomerism
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What are two types of stereoisomerism
E/Z isomerism Optical isomerism
When can E/Z isomerism occur
Only in compounds with a C=C double bond
When can optical isomerism occur
In a wider range of compounds including alkanes with no functional groups
When does Stereoisomerism around double bonds arise
Because rotation about the double bond is restricted and the groups attached to each carbon atom are therefore fixed relative to each other The rigidity is caused by the position of the π-bond’s electron density above and below the plane of the σ-bond
What are the conditions a molecule must satisfy in order to have E/Z isomerism
A C=C double bond Different groups attached to each carbon atom of the double bond
Which of but-1-ene and but-2-ene can have E/Z isomers
but-2-ene Because it has a methyl group AND a hydrogen atom on each of the carbon atoms of the double bond
What is Cis-trans isomerism
The name commonly used to describe a special case of E/Z isomerism One of the attached groups on each carbon atom of double bond must be hydrogen
Difference between a cis isomer and a trans isomer
Cis - hydrogen atoms on each carbon in double bond on SAME side of the molecule Trans - hydrogen atoms are diagonally OPPOSITE each other
In cis-trans isomerism
The cis isomer is the Z isomer The trans isomer is the E isomer
What are the Cahn-Ingold-Prelog rules of isomerism
Atoms attached to each carbon atom in double bond are given priority based upon their atomic number If groups of higher priority on same side of double bond, compound is Z isomer If groups of higher priority are diagonally placed across double bond, compound is E isomer
How does priority change as atomic number increases
Higher number, higher priority