Page 10 Flashcards
Q: Under what condition are cis-trans isomers possible for alkenes?
A: Cis-trans isomers are possible when the two groups on each end of a carbon-carbon double bond are different from each other.
What must be true about the groups attached to the carbons of a double bond for stereoisomerism to occur?
A: Each carbon of the double bond must have two different groups attached to it.
Can an alkene with identical groups on one carbon of the double bond exhibit cis-trans isomerism?
A: No, stereoisomerism requires two different groups on each carbon of the double bond.
Why is restricted rotation around the double bond important for cis-trans isomerism?
A: Restricted rotation prevents the groups on the double bond from freely interchanging positions, preserving the distinct cis and trans forms.
What is the relationship between the groups on a cis-alkene?
A: In a cis-alkene, the identical or similar groups are on the same side of the double bond.
What is the relationship between the groups on a trans-alkene?
A: In a trans-alkene, the identical or similar groups are on opposite sides of the double bond.
Why can stereoisomers of alkenes also be called diastereomers?
A: Because cis and trans isomers are stereoisomers that are not mirror images of each other.
Q: If the groups on one carbon of the double bond are X and X’, and the groups on the other carbon are Y and Y’, what must be true for cis-trans isomerism?
A: X ≠ X’ and Y ≠ Y’.
How do the physical properties of cis- and trans-isomers differ?
A: Cis-isomers generally have higher boiling points and lower melting points than trans-isomers due to differences in molecular polarity and symmetry
Why are cis-trans isomers not possible in compounds with terminal double bonds?
A: Terminal double bonds have at least one carbon with two identical hydrogen atoms, failing the requirement for different groups on each carbon.
Why are cis-trans isomers not possible in compounds with terminal double bonds?
A: Terminal double bonds have at least one carbon with two identical hydrogen atoms, failing the requirement for different groups on each carbon.
