8. Alkenes

Question 1

What is the general formula of alkenes?

Answer 1

CnH2n

Question 2

What is the arrangement of carbon in a C=C double bond?

Answer 2

• Planar arrangement of atoms

- Geometry of carbons is trigonal planar

Question 3

What is a sigma bond?

Answer 3

Head-to-head overlap of sp2 hybridised orbitals gives rise to a sigma bond

Question 4

What is a pi bond?

Answer 4

Sideways overlap of the p orbitals gives rise to a pi bond

Question 5

What is the difference in strength between sigma and pi bond?

Answer 5

A pi bond is weaker than the sigma bond due to less efficient orbital overlap

Question 6

What is rule 1 for naming E/Z isomers?

Answer 6

Assign priorities to the groups at each end of the double bond

Question 7

What is rule 2 for naming E/Z isomers?

Answer 7

If the high priority groups are on the same side (Z)

If the high priority groups are on he opposite side (E)

Question 8

Which is more stable, cis or trans?

Answer 8

Cis is slightly less stable because of steric strain

Question 9

How does the number of substitutions affect stability of alkenes?

Answer 9

The more substituted the alkene, the more stable it is.

Tetra>tri>Di>mono