Name: Preparation of a Haloalkanes
Uploaded: 2019-07-19
Duration: 5 min 52 s
Description: The haloalkanes are a group of chemical compounds derived from alkanes containing one or more halogens, and in this video, we will learn about their preparat...

Question

Explain the mechanism of Nucleophilic bimolecular substitution

(S_{N}^{2})

reaction with one example.

Accepted Answer

Bimolecular nucleophilic substitution reaction ion follows second-order kinetics, i.e., the rate depends upon the concentration of both the reactants. Consider the example of methyl chloride:

It depicts a bimolecular nucleophilic substitution ( $S_{N}^{2}$ ) reaction; the incoming nucleophile interacts with alkyl halide causing the carbon-halide bond to break and a new bond is formed between carbon and attacking nucleophile. Here it is a $C - O$ bond formed between $C$ and $- OH$ . These two processes take place simultaneously in a single step and no intermediate is formed. As the reaction progresses and the bond between the incoming nucleophile and the carbon atom starts forming, the bond between the carbon atom and leaving group weakens. As this happens, the three carbon-hydrogen bonds of the substrate start moving away from the attacking nucleophile. In the transition state, all the three $C - H$ bonds are in the same plane and the attacking and leaving nucleophiles are partially attached to the carbon. As the attacking nucleophile approaches closer to the carbon, C-H bonds still keep on moving in the same direction till the attacking nucleophile attaches to carbon and leaving group leaves the carbon.

As a result, the configuration is inverted, the configuration (See box) of carbon atom under attack inverts in much the same way as an umbrella is turned inside out when caught in a strong wind. This process is called an inversion of configuration. In the transition state, the carbon atom is simultaneously bonded to the incoming nucleophile and the outgoing leaving group. Such structures are unstable and cannot be isolated. Thus, in the transition state, carbon is simultaneously bonded to five atoms. Since this reaction requires the approach of the nucleophile to the carbon bearing the leaving group, the presence of bulky substituents on or near the carbon atom have a dramatic inhibiting effect. Of the simple alkyl halides, methyl halides react most rapidly in $S_{N}^{2}$ reactions because there are only three small hydrogen atoms. Tertiary halides are the least reactive because bulky groups hinder the approaching nucleophiles. Thus, the order of reactivity followed is: Primary halide > Secondary halide > Tertiary halide.

Explain the mechanism of Nucleophilic bimolecular substitution $(S_{N}^{2})$ reaction with one example.

Important Questions on Haloalkanes and Haloarenes

Learn and Prepare for any exam you want !

Explain the mechanism of Nucleophilic bimolecular substitution SN2 reaction with one example.

Important Questions on Haloalkanes and Haloarenes

Learn and Prepare for any exam you want !

Explain the mechanism of Nucleophilic bimolecular substitution $(S_{N}^{2})$ reaction with one example.