Other Nomenclature Systems for Functional Compounds

9 Other Nomenclature Systems

Downloaded by PENNSYLVANIA STATE UNIV on June 21, 2012 | http://pubs.acs.org Publication Date: June 1, 1974 | doi: 10.1021/ba-1974-0126.ch009

for Functional Compounds Al though substitutive nomenclature as described in Chapters 8 and 10 is recommended as the single best system of naming organic compounds, four other methods, each having limited capability, have found varying degrees of use. These, roughly in order of importance, are radicofunction al nomenclature, conjunctive nomenclature, additive nomenclature, and subtractive nomenclature. Recommended Nomenclature Practice Radicofunctional Names. In forming a radicofunctional name one species of functional group is selected and expressed as the final word of a multiword name. The preceding word or words, usually arranged in alphabetical order, describe the remainder of the molecule. C H OH (C1CH CH )20 CH SCH CH CH COC H CH CH COOCH 2

5

2

3

2

3

3

2

3

6

5

2

3

Ethyl alcohol Bis(2-chloroethyl) ether Ethyl methyl sulfide Methyl phenyl ketone Methyl propionate

A n order of precedence of functions is provided in the 1965 I U P A C Rules (Rule C-22) for use in selecting the functional group to be cited as the final word of the name when more than one species of function occurs in the molecule. HOCH CH CH CN 2

2

2

3-Hydroxypropyl cyanide preferred to 3-Cyanopropyl alcohol

Conjunctive Names. This type of nomenclature is used when the principal group in the molecule occurs in a side chain attached to a ring system and for some special reason (see Discussion) one does not wish to name the ring system as a substituting group. A conjunctive name is formed simply by connecting without hyphenation the names (as compounds) of the component portions, one cyclic and one acyclic, into which the molecule can be conceptually divided. Such juxtaposition of the two names implies that mutual 76 In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

9.

11

Other Nomenclature Systems

substitution of hydrogen has occurred in the two component compounds. The name of the cyclic compound is cited first, followed by that of the acyclic compound. CH OH


2

2-Naphthalenemethanol

3,5-Pyridinediacetic acid HOOCCH

CH COOH

r \ / '

2

CH CH CH OH 2

2

2

2-Furanpropanol

In conjunctive names the position of the principal functional group arbitrarily defines the "terminal" position of the side chain, and locations of substituents on the side chain are then indicated by Greek letters. The letter a is assigned to the "terminal" carbon atom, and lettering continues along the chain to its point of connection to the ring.

^ " N r ^ V

C

H

I

Cl

Cl

_

C

H

C

H

3

I

j3-Chloro-QJ-methyl-2-naphthaleneethanol

OH

^~CHCH COOH 2

]3,4-Dichlorocyclohexanepropionic acid

Cl

More detailed recommendations for forming conjunctive names are provided in the 1965 I U P A C Rules (Rules C-51 through C-58). Additive Names. A s the term implies, an additive name is formed by citing atoms or groups that have been added conceptually to a reference compound to convert it to the compound being named. Hydrogen so added is denoted by the prefix hydro, but any other species of atom or group added is expressed as a separate word following the name of the reference compound.

In Nomenclature of Organic Compounds; Fletcher, J., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

78

NOMENCLATURE OF ORGANIC COMPOUNDS

00

1,2-Dihydronaphthalene

Tetrahydrofuran

Br CHCHBr 2

Acetylene tetrabromide

2

CfcHsCH—CH O

Styrene oxide


2

C H N H - HC1 6

S

Aniline hydrochloride

2

Subtractive Names. Similarly i n principle to additive nomenclature, subtractive names are formed from those o f a reference compound by conceptually removing atoms or groups to produce the compound being named. The prefix de followed by the name o f an atom or group (other than hydrogen) indicates that the latter has been removed and its place taken by hydrogen—e.g., de-N-methylmorphine. The prefix didehydro signifies removal o f two hydrogen atoms, with formation o f a double bond—e.g., 7,8-didehydrocholesterol (sometimes improperly shortened to "7-dehydrocholesterol"). The prefix nor as used in specialized nomenclature o f terpene hydrocarbons indicates removal of all methyl groups attached to a ring system—e.g., norpinane. In trivial names of other natural products, especially steroids, nor as a prefix has been used to denote shortening o f a side chain or contraction o f a ring—e.g., 23-nor-5j3-cholanoic acid. In additive nomenclature the prefix homo has been used occasionally to indicate addition o f a C H group to a compound having a trivial name—e.g., homopiperonylic acid for (3,4-methylenedioxyphenyl)acetic acid, but except for natural products, especially steroids, this practice should be abandoned in favor o f systematic names wherever possible. The prefix anhydro is used in specialized nomenclature o f carbo hydrates to indicate loss o f the elements o f water from within a molecule—e.g., 3,6-anhydro-jS-D-glucopyranose; deoxy denotes replace ment o f the O H group by H—e.g., 6-deoxy-a-D-glucopyranose. 2

Discussion Generally, use o f the above methods o f nomenclature should be avoided so far as possible except for the use o f additive names involving



9.

Other Nomenclature Systems

79

the prefix hydro in naming partially or fully saturated ring systems. Systematically formed substitutive names are available and should be used for compounds that in the past have commonly been given names of the radicofunctional, conjunctive, or additive kind—e.g., ethanol (for ethyl alcohol, (methylthio)ethane (for ethyl methyl sulfide), 2-naphthylmethanol (for 2-naphthalenemethanol), 1,1,2,2-tetrabromoethane (for acetylene tetrabromide), phenyloxirane (for styrene oxide), anilinium chloride (for aniline hydrochloride), and many others. In particular, subtractive nomenclature has found very limited use and is seldom needed except with trivial names of complex naturally occurring compounds; however, the subtractive principle is still employed in officially accepted special nomenclature systems devised for terpene hydrocarbons and carbohydrates. Following a common practice in inorganic chemical nomenclature, replacement of oxygen by sulfur in organic compounds is often indicated by use of the prefix thio—e.g., thioacetic acid, thiophenol, etc. The corresponding prefixes seleno and telluro are used in the same manner. However, such nomenclature has led to many ambiguous names (thioglycolic acid is an example) and should be discontinued as far as possible in naming specific compounds. O n the other hand, generic names using thio are acceptable—e.g., thioether and thioketone, — as is the use of thio as an adjective (separate word) meaning replacement of oxygen by sulfur—e.g., thio derivative and thio analog. However, for the latter purpose the terms sulfur derivative and sulfur analog would serve equally well. The concept of oxygen replacement is also involved in names such as benzophenone oxime wherein a nitrogen-containing group is regarded as having replaced a carbonyl oxygen atom (see Chapter 32). Here again, systematically formed substitutive names such as (diphenylmethylene)hydroxylamine are much to be preferred. In brief, use of the replacement concept in organic nomenclature should be limited, as far as possible, to replacement o f carbon as described in Chapters 6 and 7. Special comment is appropriate concerning conjunctive nomenclature since this method is used extensively by Chemical Abstracts, primarily to provide improved arrangement of subject index entries (inverted form) for certain types of compounds. Because of this practice by Chemical Abstracts chemists have used conjunctive names widely in general-purpose nomenclature even though in nearly all cases substitutive names are readily available. Except for indexing, conjunctive names offer no significant advantages, and unless one is thoroughly acquainted with Chemical Abstracts indexing rules, one cannot always be certain as to when or when not to use the conjunctive type of name. Thus, substitutive names are generally to be preferred.


Other Nomenclature Systems for Functional Compounds

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