When 1-butene reacts with HCl, the major product is 2-chlorobutane. This reaction is an example of an electrophilic addition reaction, in which the HCl molecule adds across the double bond of the 1-butene molecule. The reaction can be represented as follows:

CH3CH2CH=CH2 + HCl → CH3CH2CHClCH3

The reaction proceeds via a carbocation intermediate. The HCl molecule first protonates the double bond of the 1-butene molecule, forming a carbocation. The carbocation then reacts with the chloride ion to form the final product.

The reaction of 1-butene with HCl is a classic example of an electrophilic addition reaction. This type of reaction is commonly used in organic chemistry to synthesize a variety of different compounds.