10. Alkenes

Question 1

Which is stronger: a C-C bond (made of a sigma bond) or a C=C double bond (made of sigma and pi bonds)?

Answer 1

C=C

Question 2

Bond Enthalpy for a Pi Bond: +347
Bond Enthapy for a Sigma Bond: +612
1) Which is stronger?
2) Which is more reactive?

Answer 2

1) Sigma
2) Pi

Question 3

Why is there no rotation around a C=C double bond?

Answer 3

• pi bond formed by an overlap of p orbitals
• if there was any rotation, the p orbitals would no longer overlap and the pi bond would break

Question 4

Explain why 2-bromopropane is the major product in this reaction:

Answer 4

• 2-bromopropane is made from a secondary carbocation
• 1-bromopropane is made from a primary carbocation
• Secondary carbocations are more stable than primary carbocations due to the +ve inductive effect of 2 alkyl groups in comparision to 1 alkyl group