CHAPTER 8 NUCLEOPHILIC SUBSTITUTION hen we discussed elimination reactions in Chapter 5, we learned that a Lewis base can react with an alkyl halide to form an alkene. In the present chapter, you will find that the same kinds of reactants can also undergo a different reaction,one in which the Lewis base acts as a nucleophile to substitute for the halide substituent on carbon R-X:+Y R-Y +: X Alkyl Lewis base Product of Halide halid nucleophilic anion substitution We first encountered nucleophilic substitution in Chapter 4, in the reaction of alcohols with hydrogen halides to form alkyl halides. Now we'll see how alkyl halides can them- selves be converted to other classes of organic compounds by nucleophilic substitution This chapter has a mechanistic emphasis designed to achieve a practical result. By understanding the mechanisms by which alkyl halides undergo nucleophilic substitution, we can choose experimental conditions best suited to carrying out a particular functional group transformation. The difference between a successful reaction that leads cleanly to a desired product and one that fails is often a subtle one. Mechanistic analysis helps us to appreciate these subtleties and use them to our advantage 8.1 FUNCTIONAL GROUP TRANSFORMATION BY NUCLEOPHILIC SUBSTITUTION Nucleophilic substitution reactions of alkyl halides are related to elimination reactions n that the halogen acts as a leaving group on carbon and is lost as an anion. The car- bon-halogen bond of the alkyl halide is broken heterolytically: the pair of electrons in that bond are lost with the leaving group 302 Back Forward Main MenuToc Study Guide ToC Student o MHHE Website302 CHAPTER 8 NUCLEOPHILIC SUBSTITUTION When we discussed elimination reactions in Chapter 5, we learned that a Lewis base can react with an alkyl halide to form an alkene. In the present chapter, you will find that the same kinds of reactants can also undergo a different reaction, one in which the Lewis base acts as a nucleophile to substitute for the halide substituent on carbon. We first encountered nucleophilic substitution in Chapter 4, in the reaction of alcohols with hydrogen halides to form alkyl halides. Now we’ll see how alkyl halides can them￾selves be converted to other classes of organic compounds by nucleophilic substitution. This chapter has a mechanistic emphasis designed to achieve a practical result. By understanding the mechanisms by which alkyl halides undergo nucleophilic substitution, we can choose experimental conditions best suited to carrying out a particular functional group transformation. The difference between a successful reaction that leads cleanly to a desired product and one that fails is often a subtle one. Mechanistic analysis helps us to appreciate these subtleties and use them to our advantage. 8.1 FUNCTIONAL GROUP TRANSFORMATION BY NUCLEOPHILIC SUBSTITUTION Nucleophilic substitution reactions of alkyl halides are related to elimination reactions in that the halogen acts as a leaving group on carbon and is lost as an anion. The car￾bon–halogen bond of the alkyl halide is broken heterolytically: the pair of electrons in that bond are lost with the leaving group. Alkyl halide R X Lewis base Y Product of nucleophilic substitution R Y Halide anion X Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website