10. Alkenes

Question 1

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

Answer 1

C=C

Question 2

Bond enthalpy for pi bond = +347
Bond enthalpy for sigma bond = +612
which is stronger?
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 overlap of p orbitals
• if there was any rotation, p orbitals no longer overlap, pi bond would break

Question 4

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

Answer 4

• 2-bromopropane made fom secondary carbocation
• 1-bromopropane made from primary carbocation
• secondary carbocations are more stable than primary carbocations due to +ve inductive effect of 2 alkyl groups in comparison to 1 alkyl group