IUPAC Nomenclature for Transformations - Introduction - March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 7th Edition (2013)

March's Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 7th Edition (2013)

Part II. Introduction

Part II of this book will be directly concerned with organic reactions and their mechanisms. The reactions have been classified into 10 chapters, based primarily on reaction type: substitutions, additions to multiple bonds, eliminations, rearrangements, and oxidation–reduction reactions. Substitutions are classified on the basis of mechanism as well as substrate. Chapters 10 and 13 include nucleophilic substitutions at aliphatic and aromatic substrates, respectively. Chapters 12 and 11 deal with electrophilic substitutions at aliphatic and aromatic substrates, respectively. All free radical substitutions are discussed in Chapter 14. Additions to multiple bonds are classified not according to mechanism, but according to the type of multiple bond. Additions to carbon–carbon multiple bonds are dealt with in Chapter 15; additions to other multiple bonds in Chapter 16. One chapter is devoted to each of the three remaining reaction types: Chapter 17, eliminations; Chapter 18, rearrangements; Chapter 19, oxidation–reduction reactions. This last chapter covers only those oxidation–reduction reactions that could not be conveniently treated in any of the other categories (except for oxidative eliminations).

Each chapter in Part II consists of two main sections. The first section of each chapter (except Chapter 19) deals with mechanism and reactivity. For each reaction type the various mechanisms are discussed in turn, with particular attention given to the evidence for each mechanism and to the factors that cause one mechanism rather than another to prevail in a given reaction. Following this, each chapter contains a section on reactivity, including, where pertinent, a consideration of orientation and the factors affecting it.

The second main section of each chapter is a treatment of the reactions belonging to the category indicated by the title of the chapter. It is not possible to discuss in a book of this nature all or nearly all known reactions. However, an attempt has been made to include all the important reactions of standard organic chemistry that can be used to prepare relatively pure compounds in reasonable yields. In order to present a well-rounded picture and to include some reactions that are traditionally discussed in textbooks, a number of reactions that do not fit into the above category have been included. However, certain special areas have been covered only lightly or not at all. Among these are polymerization reactions, and the preparation and reactions of heterocyclic compounds, carbohydrates, steroids, and compounds containing phosphorus, silicon, arsenic, boron, and mercury. The basic principles involved in these areas are of course no different from those in the areas more fully treated.

Each reaction is discussed in its own numbered section.1 These are numbered consecutively within a chapter, each section number is preceded by the chapter number, so that Reaction 16-1 is the first reaction of Chapter 16 and Reaction 13–21 is the 21st reaction of Chapter 13. The order in which the reactions are presented is not arbitrary, but is based on an orderly outline that depends on the type of reaction. Within each section, the scope and utility of the reaction are discussed and references are given to review articles, if any. If there are features of the mechanism that especially pertain to that reaction, these are also discussed within the section rather than in the first part of the chapter where the discussion of mechanism is more general.

II.A. IUPAC Nomenclature for Transformations

There has long been a need for a method of naming reactions. Many reactions have been given the names of their discoverers or those who popularized them (e.g., Claisen, Diels–Alder, Stille, Wittig, Cope, Dess–Martin). In the past, this was necessary because mechanisms were not well understood, and a named reaction was a convenient way to identify certain transformations. Nowadays, the reasons for assigning a name are less clear and there may be as many as 800–1000 named reactions. Some believe that this practice has gotten out of hand, while others believe it to be the best way to organize key reactions. Named reactions are useful to a point, but each name must be individually memorized, and there are many reactions that do not have such names. The IUPAC Commission on Physical Organic Chemistry produced a system for naming, not reactions, but transformations (a reaction includes all reactants; a transformation shows only the substrate and product, omitting the reagents). The advantages of a systematic method are obvious. Once the system is known, no memorization is required; the name can be generated directly from the equation. The system includes rules for naming eight types of transformation: substitutions, additions, eliminations, attachments and detachments, simple rearrangements, coupling and uncoupling, insertions and extrusions, and ring opening and closing. Only the most basic rules are given for the first three of these types, which, however, will suffice for naming many transformations.2

II.A.i. Substitutions

A name consists of the entering group, the syllable “de”, and the leaving group. If the leaving group is hydrogen, it may be omitted (in all examples, the substrate is written on the left).

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Multivalent substitutions are named by a modification of this system that includes suffixes (e.g., “bisubstitution” and “tersubstitution”).

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(Note: The nitrilo group is imgN.)

II.A.ii. Additions

For simple 1,2-additions, the names of both addends are given followed by the suffix “addition”. The addends are named in order of priority in the Cahn–Ingold–Prelog system (Sec. 4.E.i), the lower-ranking addend coming first. Multivalent addition is indicated by “biaddition”, and so on,

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Eliminations are named the same way as additions, except that “elimination” is used instead of “addition”.

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In the reaction sections of this book, IUPAC names are used for most transformations (these names will be printed in the same typeface used above), including examples of all eight types.3 As will become apparent, some transformations require more rules than we have given here.2 However, it is hoped that the simplicity of the system will also be apparent.

Two further notes: (1) Many transformations can be named using either of two reactants as the substrate. For example, the transformation methylene-de-oxo-bisubstitution above, can also be named ethylidene-de-triphenylphosphoranediyl-bisubstitution. In this book, unless otherwise noted, we will show only those names in which the substrate is considered to undergo the reactions indicated by the titles of the chapters. Thus the name we give to Reaction 11-11 (ArH + RCl → ArR) is alkyl-de-hydrogenation, not aryl-de-chlorination, although the latter name is also perfectly acceptable under the IUPAC system. (2) The IUPAC rules recognize that some transformations are too complex to be easily fitted into the system, so they also include a list of names for some complex transformations, which are IUPAC approved, but nonsystematic (for some examples, see Reactions 12–44, 18–34).