Alkenes - Stereoisomerism

Question 1

What is the difference between structural isomerism & stereoisomerism?

Answer 1

• Structural isomers are compounds with the same molecular formula but different structural formulae.
• Stereoisomers have the same structural formula but a different arrangement of the atoms in space.

Question 2

Explain the origin of E/Z isomerism in alkenes.

Answer 2

Results from restricted rotation around C=C double bonds in alkenes that have 2 different atoms/groups bonded to each C of the C=C double bond.

Question 3

Describe, in terms of CIP priorities, the arrangement of groups across the double bond of an alkene in an E-isomer.

Answer 3

The higher priority groups are on opposite sides of the double bond.

Question 4

How are cis & trans isomers related to E & Z isomers?

Answer 4

The cis isomer is the Z isomer, and the trans isomer is the E isomer.

Question 5

What is cis-trans isomerism?

Answer 5

Special case of E/Z isomerism, in which 2 of the substituent groups attached to each C atom of the C=C group are the same.

Question 6

How do you assign CIP priorities to atoms/groups in an alkene?

Answer 6

The atom/group with the higher atomic number on each C atom of the C=C double bond has the higher priority.