Question

Which of these compounds can undergo an addition reaction? Why?

1. `CH_4`
2. `C_2H_4`
3. `C_3H_8`
4. `C_4H_10`

Answer 1

Consider the bond line structure of each, in turn,

Which one has a `pi` bond?

Ethylene!

Addition reactions generally require a pi bond as a nucleophile for addition of substituents to the carbons it covers.