Direction (1-5): The alkyi halides are extremely important reagents because they undergo a large variety of reactions that make them valuable in organic synthesis. This arises from the fact that the halide ion is a weak base and is readily displaced by stronger bases. This type of reaction is an example of nucleophilic substitution \[\left( {{S}_{N}} \right)\] since the attacking reagent is a nucleophilic reagent. This type of heterolytic reaction in solution can take place by two different mechanisms, unimolecular \[\left( {{S}_{N}}1 \right)\] or bimolecular \[\left( {{S}_{N}}2 \right)\]. |
\[{{S}_{N}}1\] reaction is a two step process and in the first step, R-X ionises to give carbocation (slow process). In the second step, the nucleophile attacks the carbocation from either side to form the product (fast process). \[{{S}_{N}}1\] reaction is favoured by heavy (bulky) groups on the carbon atom attached to halogens. \[{{S}_{N}}2\] reaction is a one stage process and two molecules simultaneously undergo covalency change in the rate determining step. In the transition state, the groups OH and X are collinear and on the opposite sides of attacked carbon. \[{{S}_{N}}2\] mechanism always lead to inversion of product. \[{{S}_{N}}2\] reaction is favoured by small groups on the carbon atom attached to halogen. (I.L. Finar, Organic Chemistry Vol I. The fundamental principles Ch. 5, Sixth Edition). |
A)
B) \[{{\left( C{{H}_{3}} \right)}_{3}}C-Br\]
C) \[C{{H}_{3}}C{{H}_{2}}-I\]
D)
Correct Answer: C
Solution :
Primary alkyi halides preferably react by \[{{S}_{N}}^{2}\] mechanism.You need to login to perform this action.
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