Electropositive element nucleophilic attack

One way to look at this process is to say that the elements H and Cl added to the 7t-bond, so it can be called an addition reaction. In reality, the alkene reacts as a Brpnsted-Lowry base with the strong acid to form the C-H bond and a carbocation intermediate. In a second chemical step, the chloride cormter-ion is a nucleophile that attacks the electropositive carbon of the carbocation to form a C-Cl bond. The conversion of cyclopentene to 2 and then to 3 constitutes the mechanism of this reaction, which is the step-by-step chemical sequence of reactions that transforms cyclopentene to chlorocyclopentene. The mechanism of this reaction, as described in Chapter 7 (Section 7.8), is a two-step process in which cyclopentene reacts with HCl to give carbocation 2, which reacts with chloride ion in a second chemical step to give 3. 

---