IUPAC system

A chemical name typically has four parts in the IUPAC system of nomenclature prefix, locant, parent, and suffix. The prefix specifies the location and identity of various substituent groups in the molecule, the locant gives the location of the primary functional group, the parent selects a main part of the molecule and tells how many carbon atoms are in that part, and the suffix identifies the primary functional group. 

Simple alcohols are named by the IUPAC system as derivatives of the parent alkane, using the suffix -ol. 

Primary amines are named in the IUPAC system in several ways. For simple amines, the suffix -amine is added to the name of the alkyl substituent. You might also recall from Chapter 15 that phenylamine, C6HSNH2, has the common name aniline. 

Amines are organic derivatives of ammonia. They are named in the IUPAC system either by adding the suffix -amine to the name of the alkyl substituent or by considering the amino group as a substituent on a more complex parent molecule. 

The term dediazoniation was introduced by Bunnett as early as 1954. It is now included in the IUPAC system of naming transformations in organic chemistry (IUPAC, 1989 a). 

Dediazoniation refers to all those reactions of diazo and diazonium compounds in which an N2 molecule is one of the products. The designation of the entering group precedes the term dediazoniation, e. g., azido-de-diazoniation for the substitution of the diazonio group by an azido group, or aryl-de-diazoniation for a Gomberg-Bachmann reaction. The IUPAC system says nothing about the mechanism of a reaction (see Sec. 1.2). For example, the first of the two dediazoniations mentioned is a heterolytic substitution, whereas the second is a homolytic substitution. 

The naming of these three heterocyclic fused (5 5 5) ring systems has been carried out according to the IUPAC system of nomenclature. Some examples are given as follows compound la (Table 1) is named (3-hydroxy-4-methoxyphenylthieno[2,3-3]pyrrolizin-8-one. Compound 15a (Table 2) is dithieno[3,2-3 2, 3 - 1thiophene. Compound 23a (Table 2) is dithieno[3,2-3 2, 3 - 1pyrrole. Compound 20a (Table 2) is dithicno[3,2-3 2, 3 -r/]thiophene-4,4-dio ide. Compound 13b (Table 2) is 3,4-dimethyldithieno[3,2-3 2, 3 -i/]thiophene-7,7-dioxide. Compound 38 (Table 4) is fM, r, r-10-azatricyclo[5.2.1.01 10]deca-2,5,8-triene. Compound 39 (Table 4) is cis,cis, m-10-azatricyclo[5.2.1.01 10]deca-2,8-diene. The nomenclature of compound 40 (Table 4) is 1,4,7 triaza tricy-clo[5.2.1.01,10]decane. 

In the/flc isomer, the three chloride ions are located on the corners of one of the triangular faces of the octahedron. In the mer isomer, the three chloride ions are located around an edge (meridian) of the octahedron. The IUPAC system of nomenclature does not use this approach. A summary of the IUPAC procedures is presented in the book by Huheey, Keiter, and Keiter that is cited in the references listed at the end of this chapter. 

Physical Chemistry (third edition) by G. W. Castellan, Addison Wesley, Reading, MA, 1983, is not much in vogue these days, in part because many of his symbols do not conform to the IUPAC system. Castellan s strength is his explanations, which are always excellent. His mathematical rigour is also notable. 

Fig. 2. Nomenclature of the heme group of horseradish peroxidase according to the lUB/IUPAC system. Proton-bearing carbon atoms are numbered on the structure and can be cross-referenced with the Fischer system as follows ...

In the IUPAC system locants are placed immediately before the part of the name to which they apply for instance subunits such as pyridine-2,4-diyl and l-methylpropane-l,3-diyl. One of the few exceptions is the phenylene subunit, for example, 1,4-phenylene in XV. The IUPAC nomenclature system is always evolving and some of the details (e.g., the names of some subunits) have changed in recent years. One should use caution when using less recent nomenclature references than those listed in this text. 

The IUPAC nomenclature system recognizes that most of the common (commercial) polymers have source-based or semisystematic names that are well established by usage. IPUAC does not intend that such names be supplanted by the IUPAC names but anticipates that such names will be kept to a minimum. The IUPAC system is generally used for all except the common polymers. The IUPAC names for various of the common polymers are indicated below the more established source or semisystematic name in the following ... 

Name each of the polymers in Problem 1-1 by the IUPAC system. Indicate alternate names where applicable based on the polymer source, non-IUPAC structure system, or trade names. 

Name each of the following polymers by the IUPAC system... 

When the two radicals attached to the azo group are derived from different parent molecules, the IUPAC system places the term azo between the complete names of the (substituted) parent molecules (Rule C-911.2). This system resembles an older numbered azo bridge system. The Chemical Abstracts system names the compound as a parent molecule RH substituted by a radical R N=N— (Rule C-912.4). This system is particularly convenient for unsymmetrically substituted aliphatic azo compounds. 

When the same number and kinds of substituents are carried by the two aromatic radicals, the IUPAC system simply numbers the substituents in a conventional manner, whereas the Chemical Abstracts system names the compound as an assembly of identical units with the prefix azodi- preceding the name of the unsubstituted parent compound ... 

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 1-12 (ArH + RCI- ArFt) is alkyl-de-hydrogenation, not aryl-de-chlorination, though 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 2-44, 8-36, 9-63). 

In the IUPAC system the SnI mechanism is DN + AN or DN + An (where t denotes the rate-determining step). The IUPAC designations for the SnI and Sn2 mechanisms thus clearly show the essential differences between them AnDn indicates that bond breaking is concurrent with bond formation DN + AN shows that the former happens first. 

Both the Se2 (front) and Se2 (back) mechanisms are designated DFAE in the IUPAC system. With substrates in which we can distinguish the possibility, the former mechanism should result in retention of configuration and the latter in inversion. When the electrophile attacks from the front, there is a third possibility. A portion of the electrophile may assist in the removal of the leaving group, forming a bond with it at the same time that the new C—Y bond is formed ... 

In this mechanism the two groups leave at about the same time and bond to each other as they are doing so. The designation is Ei in the Ingold terminology and cyclo-DEDNA in the IUPAC system. The elimination must be syn and, for the four- and five-membered transition states, the four or five atoms making up the ring must be coplanar. Coplanarity... 

It is unfortunate that two systems of nomenclature are currently being used in this area. Though this author, like most in the United States, has a personal preference for the Fischer system (11) (because it retains a link with the monumental body of earlier work), the IUPAC system (12) is mandated in this chapter. To be sure, the IUPAC system has its advantages, not the least of which is the correlation of atoms between the porphyrin (12) and corrin (13) chromophore. 

In the IUPAC system, the four methine positions are conveniently numbered 5, 10, 15 and 20, and the eight remaining peripheral positions fall at 2, 3, 7, 8, 12, 13, 17 and 18. The nitrogen atoms are numbered 21 through 24. Owing to the continued use of trivial names, both in the IUPAC and classical systems of nomenclature, certain other features of porphyrin notation and isomerism need to be explained. If the eight peripheral substituents are made up of two sets of four (for example, four methyls and four ethyls), and if there is one of each on the individual pyrrole subunits (a situation which usually occurs in biologically derived porphyrins), then there are four possible so-called primary type isomers. These four isomers for the methyl/ethyl series, trivially named etioporphyrins, are shown in Scheme 1 the compounds are named etioporphyrin-I (14), etioporphyrin-II (15), etioporphyrin-III (16), and etioporphyrin-IV (17). 

The rales of the IUPAC system for naming the alkenes are as follows 1. Select as the parent structure the longest continuous chain that contains the carbon-carbon double bond then consider the compound to have been derived from this structure by replacement of hydrogen atoms by various alkyl groups. 

The parent structure is the longest continuous chain that contains the triple bond, and the positions of both the substituents and the triple bond are indicated by numbers. According to this system the simplest alkyne should be named ethyne however, this compound commonly is called acetylene. The other alkynes are usually named according to the IUPAC system. 

Unfortunately, a completely systematic method of naming aromatic compounds is not in use. The system used is a combination of trivial names and the IUPAC system. Sometimes- compounds that contain benzene rings are considered to be substituted benzenes, in which case the word benzene appears in the name of the compound along with the name of the substituent. 

Draw structural formulas for the isomers of heptane. Name the isomers by the IUPAC system. 

The IUPAC rules assign names to unbranched alkanes as shown in Table 2.2. Methane, ethane, propane, and butane are retained for CH4, CH3CH3, CH3CH2CH3, and CH3CH2CH2CH3, respectively. Thereafter, the number of carbon atoms in the chain is specified by a Latin or Greek prefix preceding the suffix -ane, which identifies the compound as a member of the alkane family. Notice that the prefix n- is not part of the IUPAC system. The IUPAC name for CH3CH2CH2CH3 is butane, not n-butane. 

As you can see, cycloalkanes are named, under the IUPAC system, by adding the prefix cyclo- to the name of the unbranched alkane with the same number of carbons as the ring. Substituent groups are identified in the usual way. Their positions are specified by numbering the carbon atoms of the ring in the direction that gives the lowest number to the substituents at the first point of difference. 

Functional class names are part of the IUPAC system they are not common names. 

One way to name carbo-cations in the IUPAC system is to add the word "cation" to the name of the alkyl group. 

Ethylene is an acceptable synonym for ethene in the IUPAC system. Propylene, isobutylene, and other common names ending in -ylene are not acceptable IUPAC names. 

We noted in Section 2.13 that the common names of certain frequently encountered alkyl groups, such as isopropyl and tert-butyl, are acceptable in the IUPAC system. Three alkenyl groups—vinyl, allyl, and isopropenyl—are treated the same way. 

A second method for naming epoxides in the IUPAC system is described in Section 16.1. 

Many simple monosubstituted derivatives of benzene have common names of long standing that have been retained in the IUPAC system. Table 11.1 lists some of the most important ones. 

Ethylene glycol and propylene glycol are common names for these two diols and are acceptable IUPAC names. Aside from these two compounds, the IUPAC system does not use the word glycol for naming diols. 

---