Question

1. Please explain, detail, the differences in the hydrohalogenation across the double bond with regards to Markovnikov and Non-Markovnikov.

2. What is the relationship between an allylic carbocation (Chapter 20) and allylic radical? Please explain in terms of resonance and delocalization. If you can provide a picture to support your explanation, that will also be acceptable.

Answer 1

1)

Hydrohalogenation Of Alkenes – Reaction Mechanism

Reaction Overview: The hydrohalogenation of alkenes involves breaking a carbon to carbon double bond, followed by the electrophilic addition of a hydrogen atom and halogen. The halide will add to the more substituted carbon following Markovnikov’s rule. The product is a haloalkane also called an alkyl halide.

Summary of Hydrohalogenation Mechanism

• Nucleophilic pi bond reaches for electrophilic H in H-X, pi bond breaks in the process
• H adds to the less substituted carbon atom following Markovnikov’s rule
• More substituted carbon is now deficient getting a formal charge of +1
• Negative halide in solution attacks the carbocation forming a bond
• Product is a haloalkane – also known as alkyl halide

Mechanism Overview and Explanation

* Hi: - +

2)An allylic radical is a resonance-stabilized radical in each of the two resonance forms of which the unpaired electron is on an allylic carbon.

eg. 1:

allylic carbon allylic carbon

eg. 2:

allylic carbon allylic carbon

The lightest allylic radical 1 is called the allyl radical.

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Allylic Carbocation

An allylic carbocation is a resonance-stabilized carbocation in each of the two resonance forms of which the formal charge of +1 is on an allylic carbon.

eg. 1:

Yo- allylic carbon allylic carbon