Alkenes and E/Z Isomerism

Question 1

What is the general formula for alkenes?

Answer 1

CnH2n

Question 2

How do you name alkenes?

Answer 2

Using the same process as you do with alkanes, but including the location of the double bond

Question 3

What are the properties of alkenes?

Answer 3

Nonpolar molecules. This means they only experience Van der Waals forces and are highly insoluble in water. As the length of an alkene’s carbon chain increases so does its melting and boiling points because the strength of the Van der Waals forces increases as the molecules get larger

Question 4

What is E/Z isomerism?

Answer 4

A form of stereoisomerism - molecules have the same structural formula, but that the atoms have a different spatial arrangement

Question 5

How do you find an E/Z isomer?

Answer 5

1. Find the highest-priority substituent bonded to each carbon in the double bond (Look at the atoms that are one bond away from each of the carbons in the double bond. Compare the atomic numbers of these atoms. Give priority to the substituent that has the atom with the highest atomic number. If the atoms one bond away from the double bond are identical, then look at the atoms that are two bonds away)
2. If the two highest-priority substituents are on the same side of the double bond axis, the molecule is a Z isomer.
3. If the two highest-priority substituents are on opposite sides of the double bond axis, the molecule is an E-isomer.