What alkene reacts the fastest with HBr?

Explanation:

The reaction involving HBr is categorized as a nucleophilic addition that unfolds in the following stages:

• Stage 1: Formation of the carbocation
• Stage 2: Creation of the product (addition of Br-)

During the initial stage, a higher substitution on the carbocation denotes greater stability. Therefore, the most stable configuration involves a tertiary carbon (as seen in tert-butene), while a primary carbon (like ethene) represents the least stability, with secondary carbon (propene) in between.

From this analysis, and considering that this reaction mechanism adheres to Markovnikov's rule, one can ascertain the relative reaction rates of alkenes.

Moreover, a reaction's speed decreases with an increase in resonance intermediates.

The initial stage in the reaction involves the alkene's double bond interacting with H of HBr. This process protonates the alkene according to Markovnikov's principle, leading to the formation of a carbocation. The rate of this reaction is influenced by the stability of the carbocation formed.

<span>So to tackle your question, apply protonation to all your alkenes based on Markovnikov's rule, and subsequently evaluate the relative stabilities of the carbocation products. A tertiary carbocation is more stable than a secondary one, meaning that an alkene yielding a tertiary carbocation will react more swiftly than one generating a secondary carbocation.


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