Alkynes are less reactive than alkenes towards addition of Br2 because of the formation of

Name: Problem 31, Chapter 19: Objective Chemistry for Engineering and Medical Entrance Examinations
Uploaded: 2022-01-28T09:04:07-08:00
Duration: 1 min 4 s
Channel: Narayan Hari
Description: Alkynes are less reactive than alkenes towards addition of Br2 because of the formation of

step 1 Alkines are less reactive. Alkines are less reactive. Alkines are less reactive than alkynes, th

Alkynes are less reactive than alkenes towards addition of...

Key Concepts

Hybridization Effects on Carbon Reactivity

The hybridization of the carbon atoms involved in ? bonds significantly affects reactivity. Alkenes, containing sp2-hybridized carbons, can better accommodate the positive charge developed in cyclic intermediates like the bromonium ion. In alkynes, the sp-hybridized carbons are more electronegative and less capable of stabilizing positive charge, making the associated cyclic intermediates less stable and the overall electrophilic addition process less favorable.

Bromonium Ion Intermediate

In the addition of bromine to unsaturated compounds, a cyclic bromonium ion intermediate is formed. For alkenes, this three-membered bromonium ion is relatively stable, facilitating the reaction. In contrast, for alkynes, formation of an analogous cyclic bromonium ion involves a vinylic character, which is destabilized due to the increased s-character of the sp-hybridized carbon atoms, rendering these intermediates less favorable and thus the overall addition reaction slower.

Electrophilic Addition Reactions

Electrophilic addition is a fundamental reaction mechanism in organic chemistry where an electrophile reacts with a multiple bond (such as a double or triple bond) to form a more saturated product. This mechanism typically involves the formation of a cyclic intermediate, with electrophiles attacking the electron-rich ? system. Understanding this process is important for predicting reactivity, regioselectivity, and stereochemistry in organic transformations.

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