Organic Chemistry

Reactions of Organic Compounds

What is a bimolecular substitution reaction?

From the last answer, you can probably guess that a bimolecular substitution reaction has two (bi-) molecules (-molecular) in the transition state. This means that the slowest step involves two molecules interacting. In the previous example, there was only one.

Let’s look at a similar substitution reaction, but instead of tBuCl, we’ll react hydroxide with MeCl:


Here the nucleophile (OH) directly displaces the leaving group (Cl), without forming a carbocation intermediate. This is because the methyl cation (CH3+) is much less stable than the tert–butyl carbocation formed in the previous question.


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