In an attempt to prepare n-propylbenzene, a chemist alkylated benzene with 1-chloropropane and aluminum chloride. However, two isomeric hydrocarbons were obtained in a ratio of 2:1, the desired n-propylbenzene being the minor component. What do you think was the major product? How did it arise?

From the given problem statement, he was attempting to prepare n-propylbenzene by alkylation benzene with 1-chloropropane and aluminum chloride, but 1-propyle benze was a major product in result.

2-Phenylpropane (Cumene)

Explanation:

Famous Friedel Craft Alkylation.

Aluminum Chloride grasped the 1-chloropropane forming an intermediate product composed of Aluminum tetrachloride and n-propylcation. It is well understood that primary carbocations are unstable and therefore undergo hydrogen shifting to attain stability. n-Propylcarbocation undergone hydrogen shifting, forming isopropylcarbocation which reacted with benzene forming 2-Phenylpropane as the major product and HCl as a byproduct.

AlCl3 + CH3CH2CH2Cl - -> AlCl4 - + CH3CH2CH2+

CH3CH2CH2 + - --> CH3CH (+) CH3

C6H6 + CH3CH (+) CH3 - --> C6H5CH (CH3) 2 + H+

AlCl4 - + H + - --> HCl + AlCl3