Explain why polynitration is not favored in this experimental procedure (microscale nitration of methyl benzoate). The reagents are methyl benzoate, sulfuric acid and nitric acid. The product is methyl 3-nitrobenzoate.
In substitution reactions, one functional group is exchanged with another group. There will be an intermediate formation for these reactions which decides the product formation. The mechanism follows most stable path.
Answer and Explanation:
In the nitration of methyl benzoate, the nitration occurs in meta position as the functional group destabilises the ring and thus does not allow the substitution in the ortho and para position. Therefore, only meta position is favoured.
There are only two possible meta positions in a ring. In the case of methyl benzoate, substitution in both the meta positions are not possible due to the steric hindrance of the ring. If there occurs a poly substitution, the product formed will not be kinetically stable.
The reaction for the meta substitution is given below.
Therefore, nitration in methyl benzoate occurs only in one meta position.
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from AQA A-Level Chemistry: Practice and Study GuideChapter 16 / Lesson 4