Chemical nomenclature is used to identify a chemical species by means of written or spoken words and enables a common language for communication amongst chemists. Nomenclature for chemical compounds additionally contains an explicit or implied relationship to the structure of the compound, in order that the reader or listener can deduce the structure from the name. This purpose requires a system of principles and rules, the application of which gives rise to a systematic nomenclature. Of course, a wide range of traditional names, semisystematic or trivial, are also in use for a core group of common compounds. Detailing the latest rules and international practice, this new volume can be considered a guide to the essential organic chemical nomenclature, commonly described as the "Blue Book". An invaluable source of information for organic chemists everywhere and the definitive guide for scientists working in academia or industry, for scientific publishers of books, journals and databases, and for organisations requiring internationally approved nomenclature in a legal or regulatory environment.
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Nomenclature of Organic Chemistry
IUPAC Recommendations and Preferred Names 2013
By Henri A. Favre, Warren H. Powell
The Royal Society of ChemistryCopyright © 2014 International Union of Pure and Applied Chemistry
All rights reserved.
GENERAL PRINCIPLES, RULES, AND CONVENTIONS
P-11 Scope of nomenclature for organic compounds
P-12 Preferred, preselected, and retained IUPAC names
P-13 Operations in nomenclature of organic compounds
P-14 General rules
P-15 Types of nomenclature
P-16 Name writing
For nomenclature purposes, a structure containing at least one carbon atom and no elements from Groups 1-12, that can be named using the principles of organic nomenclature, such as substitutive or replacement nomenclature, as described in this book is considered to be an organic compound.
The formation of a systematic name for an organic compound requires first selection and then naming of a parent structure. This basic name may then be modified by prefixes, infixes, and, in the case of a parent hydride, suffixes, which convey precisely the structural changes required to generate the compound in question from the parent structure. In contrast to such systematic names, there are traditional names which are widely used both in industry and academic circles. Examples are acetic acid, benzene, and pyridine. Therefore, when they meet the requirements of utility and when they fit into the general pattern of systematic nomenclature, these traditional names are retained.
A major new principle is elaborated in these Recommendations; the concept of 'preferred IUPAC names' (PINs) is developed and systematically applied. Up to now, the nomenclature developed and recommended by IUPAC has emphasized the generation of unambiguous names in accord with the historical development of the subject. In 1993, due to the explosion in the circulation of information and the globalization of human activities, it was deemed necessary to have a common language that would prove important in legal situations, with manifestations in patents, export-import regulations, environmental health, and safety information, etc. However, rather than recommend only a single 'unique name' for each structure, we have developed rules for assigning 'preferred IUPAC names', while continuing to allow alternative names in order to preserve the diversity and adaptability of the nomenclature to daily activities in chemistry and in science in general.
Thus, the existence of preferred IUPAC names does not prevent the use of other names to take into account a specific context or to emphasize structural features common to a series of compounds. Preferred IUPAC names (PINs) belong to a 'preferred IUPAC nomenclature'. Any name other than a preferred IUPAC name, as long as it is unambiguous and follows the principles of the IUPAC recommendations herein, is acceptable as a 'general IUPAC name', in the context of a 'general IUPAC nomenclature'.
The concept of preferred IUPAC names is developed as a contribution to the continuing evolution of the IUPAC nomenclature of organic compounds. This book (Recommendations 2013) covers and extends the principles, rules, and conventions described in two former publications: Nomenclature of Organic Chemistry, 1979 Edition (ref. 1) and A Guide to IUPAC Nomenclature of Organic Compounds, Recommendations 1993 (ref. 2). In a few instances, the 1979 rules and the 1993 recommendations have been modified to achieve consistency within the entire system. In case of divergence among various sets of recommendations, these 2013 Recommendations prevail.
P-11 SCOPE OF NOMENCLATURE FOR ORGANIC COMPOUNDS
For nomenclature purposes we consider all compounds containing carbon as the principal element to be organic compounds as qualified above (see P-10). Oxygen, hydrogen, and nitrogen are the three elements usually associated with carbon to form the system of functional or characteristic groups. Other elements, among them the halogens and sulfur, complete the basic core of elements found in organic compounds. Substitutive nomenclature was first applied to compounds containing this set of atoms. The success of this type of nomenclature was such that it was extended to all elements of Groups 14, 15, 16, 17, and in Group 13, to boron; it could be extended to all elements of Group 13.
The ending 'ane', characteristic of alkanes, was borrowed from methane, ethane, etc., and attached to terms forming the roots of the names of the various elements, for example sulfane, FbS; phosphane, PFfi; silane, SiFfi; alumane, AIH3. The resulting names constitute the basis of substitutive nomenclature; this treatment of parent hydrides is called generalized 'ane' nomenclature because all the rules applicable to alkanes are applicable to all hydrides of the elements of Groups 13, 14, 15, 16, and 17. The nomenclature of the carbon hydrides may be conveniently termed 'carbane nomenclature'; whereas the term 'heterane nomenclature' covers the hydrides of elements other than carbon. Names of monouclear parent hydrides are listed in Table 2.1 in Chapter P-2.
Organometallic compounds, i.e., compounds in which one or more carbon atom(s) is (are) directly attached to a metal atom, have been regarded as organic compounds for nomenclature purposes. This association is maintained in these recommendations (see P-69), for the metals, semimetals, and nonmetals included in Groups 13, 14, 15, 16, and 17. However, the nomenclature for other organic derivatives of the elements in Groups 1 through 12 is considered as part of the nomenclature of inorganic compounds.
Likewise, IUPAC preferred names for polymers and IUPAC preferred names for Natural Products and related compounds are outside the scope of this book. The former is to be developed in conjunction with the Polymer Committee on Polymer Terminology and the latter in conjunction with the IUPAC-IUB Joint Commission on Biochemical Nomenclature.
The construction of systematic names is based on general nomenclature operations and rules, and on operations and rules specific to different types of nomenclature. These aspects are discussed in the following sections.
P-12 PREFERRED, PRESELECTED, AND RETAINED IUPAC NAMES
P-12.1 Preferred IUPAC names
P-12.2 Preselected names
P-12.3 Retained names
P-12.1 Preferred IUPAC names
Preferred IUPAC names are names for structures or structural components that are preferred among two or more names for the same structure generated from two or more recommended IUPAC rules for organic compounds or the many synonyms that have been coined and used over the years.
Preferred IUPAC names, or PINs for short, are names selected according to the set of principles, conventions, and rules given herein. They originate from the strict application of the rules; in this sense, they can be referred to as 'single names'. All preferred IUPAC names for organic compounds are identified by the parenthetical abbreviation '(PIN)' following the name. Names used in the past, but now discarded or no longer recommended, are placed in parentheses and preceded by the word 'not'. Names of organic compounds based on aluminium, gallium, indium, and thallium are not followed by the parenthetical abbreviation (PIN), because the decision to choose between a name based on organic or inorganic principles has not yet been reached.
It is necessary to select a preferred alternative in many instances in the construction of the names of organic compounds. Preferred IUPAC names are given to parent structures; characteristic groups denoted by prefixes and suffixes used in PINs are designated as preferred prefixes or suffixes. They also result from the choice to be made among the different types of nomenclature, for example, substitutive nomenclature, functional class nomenclature, and multiplicative nomenclature; and among the different types of operations, for example substitutive, additive, and subtractive.
Most commonly, a parent structure is a parent hydride, i.e., a structure containing, in addition to one or more hydrogen atoms, a single atom of an element, for example, methane; or a number of atoms (alike or different) linked together to form an unbranched chain, for example, pentane; or a monocyclic or polycyclic ring system, for example, cyclohexane and quinoline. Methane is a retained name (see P-12.3) that is preferred to the systematic name 'carbane', a name never recommended to replace methane, but used to derive the names 'carbene' and 'carbyne' for the radicals H2C2· and HC3·, respectively. Similarly, the retained names 'ethane', 'propane', and 'butane' were never replaced by systematic names 'dicarbane', tricarbane', and 'tetracarbane' as recommended for analogues of silane, 'disilane'; phosphane, 'triphosphane'; and sulfane, 'tetrasulfane'. The name 'pentane' is formed by application of P-21.2.1 and is marked as the preferred IUPAC name, or PIN, even though no rule has been cited giving an alternative name. The same reasoning applies to cyclohexane, an IUPAC name resulting from the application of P-22.1.1. The name 'quinoline' is a retained name that is preferred to the alternative systematic fusion names '1-benzopyridine' or 'benzo[b]pyridine'.
It is sometimes convenient to employ parent hydrides of more complex structure, such as ring or ring-chain assemblies, for example biphenyl and styrene. The name '1,1'-biphenyl' results from the application of Rule P-28.2.1; it is the preferred IUPAC name and the locants '1,1" are compulsory; the name 'biphenyl', without locants, can be used in general IUPAC nomenclature. The name 'styrene' is a retained name acceptable in general IUPAC nomenclature as being clear and unambiguous along with the substitutive names 'vinylbenzene', 'phenylethene', and 'phenylethylene'. The name 'ethenylbenzene' is the preferred IUPAC name (PIN).
A special class of parent structures having retained names (see P-12.3) is called functional parent compounds, for example, phenol and acetic acid. These two names are preferred IUPAC names; the corresponding systematic alternatives, benzenol and ethanoic acid, may be used in general IUPAC nomenclature. On the other hand, although acetone is a retained name recommended for general nomenclature, the preferred IUPAC name is the substitutive name propan-2-one.
In order to generate the parent structure from a compound to be named, various formal operations must be carried out. For example, in naming the structure below, the parent hydride 'pentane' is formally derived by replacing the oxygen and chlorine atoms by the appropriate number of hydrogen atoms. When constructing the name, the formal operation is reversed; the suffix 'one' and the prefix 'chloro', indicating substitution of the hydrogen atoms of pentane, are attached to the name of the parent hydride to give the name '5-chloropentan-2-one'. Suffixes and prefixes can represent a number of different types of formal operations on the parent structure. Frequently, the suffix or prefix denotes the attachment of a characteristic group (functional group), for example, 'one' or 'oxo' for =O. A prefix may also describe a group derived from a parent hydride, for example 'pentyl', CH3-CH2-CH2-CH2-CH2-, from pentane.
The substitutive operation, described in P-13.1, is the operation used most extensively in organic nomenclature. Indeed, the comprehensive nomenclature system based largely on the application of this operation to parent structures is, for convenience, termed substitutive nomenclature, although this nomenclature also involves many of the other types of operations described in P-13. Substitutive nomenclature is the set of substitutive names, principles, conventions, and rules used for name construction. Examples of substitutive and other nomenclature operations are shown in Table 1.2
Another type of nomenclature expresses the principal characteristic group not as a suffix but as a term denoting its functional class cited in a name as a separate word; in Table 1.2, the name 'ethyl propyl ether' is a typical functional class name based on the functional class name 'ether'. The corresponding substitutive name '1-ethoxypropane' is constructed by using the prefix 'ethoxy' and the parent hydride name 'propane'.
Substitutive and functional class names are written differently. Generally, substitutive names are unitary names that combine prefixes, names of parent hydrides, endings, and suffixes in one word. In contrast, a functional class name is written as separate words [in English], even though the part describing the parent hydride or the modified parent hydride is the result of the same operations used to construct substitutive names.
The great majority, if not all, of organic compounds can be named in accordance with the principles of substitutive and functional class operations. However, in these recommendations, where there is a choice, names obtained by the substitutive operation are preferred IUPAC names. In Table 1.2, examples 1, 2, and 3 illustrate this preference. The substitutive names 1-ethoxypropane and 4-chloropentan-2-one are preferred to the functional class names based on the names of the corresponding class, ether and ketone, ethyl propyl ether and 2-chloropropyl methyl ketone, respectively. In contrast, a functional class name is preferred for the ester 'trimethyl phosphite' to the substitutive name trimethoxyphosphane. Esters, along with acid halides, anhydrides, amine and oxides linked to a nitrogen atom are preferably named by using functional class nomenclature; substitutive nomenclature is less preferred for naming these compound classes.
Other types of operations are widely used, alone or along with substitutive nomenclature. There are two major types of replacement operations, the skeletal replacement operation (often referred to as skeletal replacement nomenclature or simply 'a' nomenclature) and functional replacement nomenclature. The former is used as a necessary complement in order to introduce heteroatoms into cyclic hydrocarbons and to avoid highly complex prefixes in names for acyclic systems. For example, the name '2,5,8,11-tetraoxatridecane' formed by skeletal replacement is preferred to the substitutive name '1-ethoxy-2-[2-(methoxyethoxy)ethoxy]ethane' (see Table 1.2, example 6). The latter is used to derive a very large number of suffixes and prefixes from basic oxygen names. Additive and subtractive operations have been extended for naming radicals and ions. They are the sole method for modification of the degree of hydrogenation, by adding or subtracting pairs of hydrogen atoms. Examples 4 and 5 illustrate this metholodogy. The conjunctive operation eliminates hydrogen atoms from two different parent structures and then combines them; this method is used to name parent hydrides composed of repeated identical units or to link rings and chains under specific conditions. Example 9 in Table 1.2 illustrates such an operation; in IUPAC nomenclature, however, a substitutive name is always preferred to a conjunctive name, for example '2-(1H-indol-l-yl)acctic acid' is preferred to '1H-indole-1-acetic acid' (see P-51.1.2).
A nomenclature embraces the major operations along with the principles, conventions, and rules necessary to construct names of a particular type. Substitutive nomenclature and functional class nomenclature have been discussed above. Replacement nomenclature and conjunctive nomenclature also require specific principles, conventions, and rules. In contrast, additive and subtractive operations do not correspond to nomenclatures in their own right, but are necessary complements to other nomenclatures.
It is very important to recognize that, in general, the rules of the nomenclature of organic compounds are written in terms of classical valence bonding. The principles and general rules for the nomenclature of organic compounds are described in this Chapter. Substitutive nomenclature is then elaborated in Chapter P-2 (parent hydride names), in Chapter P-3 (endings, suffixes, and prefixes), and in Chapter P-4 (selection rules for parent structures and unique names). Chapter P-5 describes selection rules for construction of preferred IUPAC names. In Chapter P-6 the naming of compounds arranged in classes and groups related to the Periodic Table (Groups 13-17) is described. In Chapter P-7, nomenclature for radicals, ions, and related species is discussed. Chapter P-8 describes isotopic modifications of organic compounds. Chapter P-9 deals with configuration and conformation specification and Chapter P-10 deals with natural products. Preferred IUPAC names (PINs) for the natural products in Chapter P-10 are not identified. Although most of the names are in fact generally accepted, there is a nebulous grey area where a distinction between a natural product name and a systematic name based solely on principles of organic nomenclature has not been defined. This likely will be the task of a future project consisting of organic and biochemical nomenclaturists.
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Table of Contents
General Principles, Rules, and Conventions; Parent Hydrides; Characteristic (Functional) and Substituent Groups; Rules for Name Construction; Selecting Preferred IUPAC Names and Constructing Names of Organic Compounds; Applications to Specific Classes of Compounds; Radicals, Ions, and Related Species; Isotopically Modified Compounds; Specification of Configuration and Conformation; Parent Structures for Natural Products and Related Compounds; References; Appendix 1; Appendix 2; Appendix 3