Polar reactions under basic conditions

Now that you have learned how to identify the mechanistic class of a particular reaction, you are ready to learn how to write the mechanism itself. This chapter is devoted to polar mechanisms that occur under basic conditions. Archetypical mechanisms will be presented and discussed so that you become familiar with the patterns of reactivity of organic compounds under basic conditions. 

Many of the reactions that will be discussed in this and later chapters are name reactions. Name reactions are used as examples in this book simply because they are widely used reactions, not because you need to know the name of any reaction to be able to draw a mechanism for it. In fact, one of the goals of this text is to show you that you can draw a mechanism for any reaction whether or not you have seen it previously. 

Electrophiles that have leaving groups (X) attached to C(sp3) usually undergo substitution or elimination reactions. In a nucleophilic substitution reaction, a nucleophile-electrophile cr bond replaces the electrophile-X cr bond. 

In an elimination reaction, the leaving group X (with its associated pair of electrons) and an electropositive group E (usually H) are removed from a compound. The most common kind of elimination is / -elimination, in which E and X are attached to adjacent atoms and a new 77 bond is formed between those atoms in the product. 

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