Addition of Hydrogen Chloride to 1,3-Cyclopentadiene

Addition of Hydrogen Chloride to 1,3-Cyclopentadiene THE OVERALL REACTION  

Step 1 A proton is transferred from HCl to a carbon at the end of the diene system to give an allylic carbocation. 

Step 2 Chloride ion acts as a nucleophile and bonds to the positively charged carbon of the carbocation. 

Carbons 1 and 4 of 1,3-cyclopentadiene are equivalent and give the same carbocation on protonation. Likew/ise, carbons 2 and 3 are equivalent. Write the structure of the carbocation formed by protonation of C-2 or C-3 to verify that it is not allylic and therefore not as stable as the one formed by protonation of C-1 or C-4. 

Both resonance contributors of the allylic carbocation from 1,3-cyclopentadiene are equivalent and attack by chloride at either of the carbons that share the positive charge gives the same product, 3-chlorocyclopentene. 

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