Stereoisomerism Flashcards
What are stereoisomers?
Molecules with the same structural formula but a different arrangement of the atoms in space
What are the two types of stereoisomerism?
E/Z isomerism and optical isomerism
Where does E/Z isomerism occur?
In compounds with a C=C double bond
Where does optical isomerism occur?
In a wide range of compounds, including alkanes with no functional groups
Why is there stereoisomerism around double bonds?
Rotation about the double bond is restricted and the groups attached to each carbon atom are therefore fixed relative to each other
Why is there rigidity around the double bond?
Due to the position of the pi bond’s density above and below the plane of the sigma bond
What are the two conditions for E/Z isomerism to occur?
1) A C=C double bond
2) Different groups attached to each carbon atom of the double bond
What is cis-trans isomerism?
A special case of E/Z isomerism
What is the condition for cis-trans isomerism to occur?
One of the attached groups on each carbon atom of the double bond must be the same
What is a cis isomer?
An isomer with the same bonds on the same side of the molecule
What is a trans isomer?
An isomer with the same bonds diagonally opposite each other
What type of isomer is cis?
Z isomer
What type of isomer is trans?
E isomer
What is Cahn-Ingold-Prelog nomenclature used for?
Isomeric compounds containing C=C bonds that can’t be classified as either cis or trans
What is Cahn-Ingold-Prelog nomenclature?
A naming system where each carbon atom in a double bond are given a priority based on their atomic number
What are the two rules of Cahn-Ingold-Prelog nomenclature?
1) If groups of higher priority are on the same side, the compound is a Z isomer
2) If groups of higher priority are diagonally placed across the double bond, the compound is an E isomer
What is the relationship between atomic number and priority?
The higher the atomic number, the higher the priority
What happens if two atoms attached to one carbon atom in a double bond are the same?
You will need to continue down the branches to find the first point of difference, and the group with the higher atomic number at the first point of difference has the higher priority
