1. Isomers
Section 1.1 and 1.2

2. Structural Isomerism Structural Isomerism
When two molecules each have the same numbers and types of atoms but these atoms are bonded in different ways
Ex: There are 2 alkanes that have the molecular formula C4H10

3. Isomerism

4. Cis- Trans Isomerism Stereoisomers
Have the same kind and number of atoms bonded in the same order but have different arrangements in space. They are distinct compounds with different properties. They must have a double bond.
These two pentene structures represent two different compounds because the molecule cannot rotate around the double bond.

5. Cis Vs. Trans Cis-Isomer Trans-Isomer
Has matching alkyl groups located on the same side of the double bond
Trans-Isomer
Has the groups located on opposite sides of the double bond

6. Practice 1. Name the following stereoisomer Cis-pent-2-ene
Trans-pent-2-ene
2. Draw structural formulas for
cis-1,2-dichloroethene and trans-1,2-dichloroethene