Scope and Organization of Review

In this review we have gathered the important work on quantitative and mechanistic aspects of electrophilic aromatic reactivity of heterocycles. We have concentrated in particular on acid-catalyzed hydrogen exchange, nitration, and gas-phase elimination, these being the major efforts of our own research groups. However all other electrophilic substitution reactions are covered for completeness. 

The book is divided into two parts Part I (Chapters 2-5) is concerned with individual reactions, and Parts II and III (Chapters 6-12) with groups of related compounds. 

Part I commences with hydrogen exchange, both because this is the simplest electrophilic substitution, and because the studies can be and have been extended over a far wider range of experimental conditions, and substrates, than any other electrophilic substitution. Chapter 3 deals with nitration, and Chapter 4 with other electrophilic substitutions. Chapter 5 is devoted to a study of the formation of side-chain carbocations, the results of which are of great importance in the interpretation of heteroaromatic reactivity. 

Parts II (Five-Membered Heterocyclic Rings) and 111 (Six-Membered Heterocyclic Rings) are organized along classical lines Monocyclic five-membered rings with one heteroatom (Chapter 6), monocyclic five-mem-bered rings with two or more heteroatoms (Chapter 7), polycyclic com- 

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