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I'm not an expert teacher or lecturer of chemistry. I was only a student from SMA NEGERI 15 SURABAYA who had been one of the Bronze Medalist Participants of Olimpiade Sains Nasional X (2011) of Chemistry In Manado, North Sulawesi, 11 - 16 September 2011 and graduated in 2012. Now, I'm studying at Universitas Airlangga in Surabaya, Indonesia. I do love chemistry and I would like to help them who had difficulties in studying chemistry. That's why, please understand me if you found some misconcepts in my entries. Suggestions are always necessary in order to develop this blog. And I'm sorry because my English isn't so well.

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Sunday, January 01, 2012

Nucleophilic Substitution Part II : Sn2 Reaction

Contrast with SN1, SN2 is a type of nucleophilic substitution where a lone pair from a nucleophile attacks an electron deficient electrophilic center and bonds to it, expelling another group called a leaving group. Thus the incoming group replaces the leaving group in one step. Since two reacting species are involved in the slow, rate determining step of them reaction, this leads to the name bimolecular nucleophilic substitution, or SN2.

SN2 happens mostly in a primary carbon. Contrast with SN1 which is happened mostly in tertiary carbon. See the picture below:



The picture above tells us that the fastest reaction happens in primary carbon. This is happened because of the steric effect of a compound. An example of SN2 reaction is as follows:



The configuration of the compound will be changed because of reaction. This is what we called as Walden Inversion. You can see it in the picture above. Based on the description above, the law of rate reaction can be formulated as r = k [RX] [Nu].

The best solvent to facilitate the SN2 reaction is an aprotic polar solvent. For example is DMF, DMSO, HMPA, etc. This is because the protic solvent like water will make a solvation effect to the nucleophile so that the nucleophile will be hard to attact the compound. Of course polar solvent is needed to facilitate the ionization.


N,N-Dimethyl Formamide (DMF)


Dimethyl Sulfoxide (DMSO)


Hexamethyl Phosphoramide (HMPA)



Energy Diagram of SN2 Reaction
(Source: http://www.ipfw.edu/chem/261/261Fall03/261nt02l_files/image053.gif)

Further Reading . . .
Wikipedia
Riswiyanto. Kimia Organik. Penerbit Erlangga


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