Addition of HCl to Alkenes to Give Alkyl Chlorides

by James

Description: Treatment of alkenes with hydrochloric acid (HCl) will result in the formation of alkyl chlorides. The chlorine always ends up at the more substituted carbon of the alkene, since protonation of the alkene will result in the more stable carbocation.

Notes: Note that this reaction is “Markovnikoff selective”. Since it goes through a carbocation, rearrangements are possible.

Examples: 

Notes: When a secondary carbocation is formed adjacent to a tertiary or quaternary carbon, rearrangements are possible. Note the third example – where Markovnikoff’s rule gives no clear preference a mixture will be obtained.

Mechanism: Electrons from the C1-C2 π bond attack the hydrogen of HCl, expelling the Cl anion and leading to the formation of a carbocation (Step 1, arrows A and B). Note that the most stable carbocation is formed preferentially. The chloride anion then attacks the carbocation, leading to formation of the alkyl chloride (Step 2, arrow C).

Notes: 

 

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Kathryn Manly

Hi James, I was wondering how you can tell if and when a reaction is regio-selective requires application of the Markovnikoff Rule (ie. if reaction will form a markovnikoff or anti-markovnikoff product). Does the regio-chemistry of a reaction also get affected by what reagents are used too?

I’m preparing for my ORG-2 Exam #2 on Conjugated Compounds & Dienes Reactions, Aromatic Compounds & Benzene Aromaticity, & E.A.S. reactions, but find my self needing to refer back to ORG-1 reactions in regards and how the reagents are used in reactions and how they are supposed to react similarly to the reactions covered in ORG-1. Can you recommend an efficient and effective approach please?

Thank you in advance for your time and efforts. This entire website has been not my one and only supplement resource to my organic chemistry courses! I have referred everyone I know who is learning, teaching and/or curious about chemistry to your Master Organic Chemistry website! I just got my first A on a ORG-CHEM Exam because of help from this site. Thanks for all the great help, summaries and guides!

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