Hydrocarbons are compounds composed of carbon and hydrogen atoms. Alkanes are hydrocarbons. As the number of carbons increases in straight-chain alkanes, there is a steady gradation of properties which can be easily compared and predicted. The properties of branched alkanes vary considerably and are hard to predict because of other intervening forces that come into play. The boiling points of a few alkanes are given below:
Alkenes can undergo free radical substitution reactions with halogens. Which of the following best represents a chain propagation step during the free radical chlorination of methane?