The Generalized Electrophilic Addition
- Page ID
- 1153
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Electrophilic addition is a reaction between an electrophile and nucleophile, adding to double or triple bonds. An electrophile is defined by a molecule with a tendency to react with other molecules which contain a pair of electrons which can be donated. Thus, it is an "electron lover." A nucleophile is a molecule that possesses a pair of electrons that can be easily shared. In essence, all nucleophiles are Lewis bases that attack Lewis acid (Lewis acids).
Introduction
In a general, during an electrophilic addition reaction, a pi bonds is removed and two new sigma bonds are created. There are multiple variations of electrophilic addition reactions, and therefore a variety of very useful products can be made. The final produce of an electrophilic addition is dependent on the reagents used for the reaction. One such electrophilic addition reaction is known as a halohydrination and forms a haloalcohol, more commonly known as a halohydrin.
Step 1
In the first step of the mechanism the electrophilic addition of bromine to the an alkene, forms a cyclic bromonium ion. For more information about the cyclic Bromonium Ion please look at Electrophilic Addition of Halogens to Alkenes.
Step 2
Next, in an SN2 reaction, a nucleophilic water molecule attacks the backside of the bromonium ion at the more substituted carbon and pushes the bromine atom onto the less substituted carbon. In general the regiochemistry of this reaction follows Markovnikov’s rule (Troll, T). As a result the Br and the H2O group are anti to each other. The nucleophile attacks the more substituted carbon, because the carbon is more positively polarized than the other carbon.
Step 3
The final step of the mechanism is an acid-base reaction, where there is a loss of a proton from the oxygen to the solvent (water) to form the neutral halohydrin product. In this case, a bromohydrin is the product of the addition reaction.
Final Product
Finally we are left with the trans-2-Bromocyclopentanol and hydrobromination. Here's the entire mechanism in gumdrop form. (Orange = C, Yellow = H, Red = Br, White = O)
References
- Vollhardt, Peter, and Neil E. Schore. Organic Chemistry: Structure and Function. 5th ed. New York: W. H. Freeman & Company, 2007
- Troll, T. "Hydroxy-and Alkoxybromination of Alkenes." Science of Synthesis 35 (2006): 471.
Problems
Just for some extra practice try and answer the following questions
1. What is the product for the following reaction
2. What is the product for the following reaction
3. Write the products (hint what acts as an electrophile and what acts as the nucleophile)
4. What is the stereochemistry and the Regiochemistry of a halohydrin formation?
5. In Markovnikov Addition the electrophile attacks the more substituted carbon and the nucleophile attacks the less substituted carbon?
A. True
B. False
Answers
1.
2.
plus isomers
3.
4. Stereochemistry: Anti-Addition & Regiochemistry: Markovnikov
5.B. False
Contributors
- Simarjit Batth (UCD)