Substitution vs. Elimination Identifying the Reagent

37 Draw the mechanism for each of the following reactions NaOMe  

38 In the next chapter, we will learn a method for preparing alkynes (compounds containing C C triple bonds). In the following reaction, a dihalide (a compound with two halogen atoms) is treated with an excess of strong base (sodium amide), resulting in two successive E2 reactions. Draw the mechanism for this transformation. 

Substitution and elimination reactions are almost always in competition with each other. In order to predict the products of a reaction, it is necessary to determine which mechanisms are likely to occur. In some cases, only one mechanism will predominate  

In other cases, two or more mechanisms will compete for example  

Don t fall into the trap of thinking that there must always be one clear winner. Sometimes there is, but sometimes there are multiple products. The goal is to predict all of the products and to predict which products ate major and which are minor. To accomplish this goal, three steps are required  

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