2.9 Applying the IUPAC Rules: The Names of the CaHi isomers A BRIEF HISTORY OF SYSTEMATIC ORGANIC NOMENCLATURE he first successful formal system of chemical pounds can have the same name, it is incorrect to be- nomenclature was advanced in France in 1787 lieve that there is only a single IUPAC name for a par to replace the babel of common names which ticular compound. then plagued the science. Hydrogen (instead of"in- The 1993 IUpac recommendations and theil flammable air" )and oxygen (instead of"vital air") more widely used 1979 predecessors may both be are just two of the substances that owe their modern accessed at the same web site names to the proposals described in the Methode de nomenclature chimique. It was then that important www.acdlabs.com/iupadnomenclature compounds such as sulfuric, phosphoric, and carbonic acid and their salts were named the guidelines were The IUPAC rules are not the only nomenclature more appropriate to inorganic compounds; it was not stem in use today. Chemical Abstracts Service sur- until the 1830s that names reflecting chemical com- veys all the worlds leading scientific journals that position began to appear in organic chemistry ublish papers relating to chemistry and publishes In 1889, a group with the imposing title of the brief abstracts of those papers. The publication International Commission for the Reform of Chemical Chemical Abstracts and its indexes are absolutely es- try. For Nomenclature was organized, and this group in turn, Chemical Abstracts nomenclature was very similar to ponsored a meeting of 34 prominent European IUPAC nomenclature but the tremendous explosion hemists in Switzerland in 1892. Out of this meeting arose a system of organic nomenclature known as the Chemical Abstracts to modify its nomenclature so Geneva rules. The principles on which the Geneva that its indexes are better adapted to computerized rules were based are the forerunners of our present searching This means that whenever feasible, a com- ystem 1911, but the intrusion of World War I prevented any ent from any of the several IUPAC names. In general national Union of Chemistry was established in 1930 and undertook the necessary revision leading to pub. chemical structure and its IUPAC name than its Chem- lication in 1930 of what came to be known as the ical Abstracts name. Liege rules It is worth noting that the generic name of a After World War I, the International Union of drug is not directly derived from systematic nomen- Chemistry became the International Union of Pure clature. Furthermore, different pharmaceutical com- and Applied Chemistry(known in the chemical com- panies will call the same drug by their own trade munity as the /UPAO). Since 1949, the IUPAC has is ame, which is different from its generic name. Generic names are invented on request (for a fee)by sued reports on chemical nomenclature on a regular the U.S. Adopted Names Council, a private organiza- basis. The most recent IUPAC rules for organic chem istry were published in 1993. The IUPAC rules often the american pharmaceutical association. and the pound. Thus although it is true that no two com- I.S. Pharmacopeial Convention In this case, the longest continuous chain has five carbon atoms; the compound is named as a derivative of pentane. The key word here is continuous. It does not matter whether the carbon skeleton is drawn in an extended straight-chain form or in one with many bends and turns. All that matters is the number of carbons linked together in an Step 2 Identify the substituent groups attached to the parent chain. The parent pentane chain bears a methyl( CH3) group as a substituent. Back Forward Main MenuToc Study Guide ToC Student o MHHE Website
In this case, the longest continuous chain has five carbon atoms; the compound is named as a derivative of pentane. The key word here is continuous. It does not matter whether the carbon skeleton is drawn in an extended straight-chain form or in one with many bends and turns. All that matters is the number of carbons linked together in an uninterrupted sequence. Step 2 Identify the substituent groups attached to the parent chain. The parent pentane chain bears a methyl (CH3) group as a substituent. 2.9 Applying the IUPAC Rules: The Names of the C6H14 Isomers 63 A BRIEF HISTORY OF SYSTEMATIC ORGANIC NOMENCLATURE The first successful formal system of chemical nomenclature was advanced in France in 1787 to replace the babel of common names which then plagued the science. Hydrogen (instead of “in- flammable air”) and oxygen (instead of “vital air”) are just two of the substances that owe their modern names to the proposals described in the Méthode de nomenclature chimique. It was then that important compounds such as sulfuric, phosphoric, and carbonic acid and their salts were named. The guidelines were more appropriate to inorganic compounds; it was not until the 1830s that names reflecting chemical composition began to appear in organic chemistry. In 1889, a group with the imposing title of the International Commission for the Reform of Chemical Nomenclature was organized, and this group, in turn, sponsored a meeting of 34 prominent European chemists in Switzerland in 1892. Out of this meeting arose a system of organic nomenclature known as the Geneva rules. The principles on which the Geneva rules were based are the forerunners of our present system. A second international conference was held in 1911, but the intrusion of World War I prevented any substantive revisions of the Geneva rules. The International Union of Chemistry was established in 1930 and undertook the necessary revision leading to publication in 1930 of what came to be known as the Liège rules. After World War II, the International Union of Chemistry became the International Union of Pure and Applied Chemistry (known in the chemical community as the IUPAC). Since 1949, the IUPAC has issued reports on chemical nomenclature on a regular basis. The most recent IUPAC rules for organic chemistry were published in 1993. The IUPAC rules often offer several different ways to name a single compound. Thus although it is true that no two compounds can have the same name, it is incorrect to believe that there is only a single IUPAC name for a particular compound. The 1993 IUPAC recommendations and their more widely used 1979 predecessors may both be accessed at the same web site: www.acdlabs.com/iupac/nomenclature The IUPAC rules are not the only nomenclature system in use today. Chemical Abstracts Service surveys all the world’s leading scientific journals that publish papers relating to chemistry and publishes brief abstracts of those papers. The publication Chemical Abstracts and its indexes are absolutely essential to the practice of chemistry. For many years Chemical Abstracts nomenclature was very similar to IUPAC nomenclature, but the tremendous explosion of chemical knowledge in recent years has required Chemical Abstracts to modify its nomenclature so that its indexes are better adapted to computerized searching. This means that whenever feasible, a compound has a single Chemical Abstracts name. Unfortunately, this Chemical Abstracts name may be different from any of the several IUPAC names. In general, it is easier to make the mental connection between a chemical structure and its IUPAC name than its Chemical Abstracts name. It is worth noting that the generic name of a drug is not directly derived from systematic nomenclature. Furthermore, different pharmaceutical companies will call the same drug by their own trade name, which is different from its generic name. Generic names are invented on request (for a fee) by the U.S. Adopted Names Council, a private organization founded by the American Medical Association, the American Pharmaceutical Association, and the U.S. Pharmacopeial Convention. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
CHAPTER TWO Alkanes ep Number the longest continuous chain in the direction that gives the lowest number to the substituent group at the first point of branching The numbering scheme CH3 CH3 is equivalent to CH3 CHCH2CH2CH3 CH count five carbon atoms in their longest continuous chain and bear as a substituent at the second carbon. An alternative numbering sequence that begins at the other end of the chain is incorrect: CH3CHCH2CH,CH3 (methyl group attached to C-4) H Write the name of the compound. The parent alkane is the last part of the name and is ceded by the names of the substituent groups and their numerical locations (locants) phens separate the locants from the word CH3 CHCH,CH,CH The same sequence of four steps gives the IUPAC name for the isomer that ha methyl group attached to the middle carbon of the five-carbon chain CH3CH CHCH CH3 IUPAC name: 3-methylpentane Both remaining C6Hi4 isomers have two methyl groups as substituents on a four- carbon chain. Thus the parent chain is butane. When the same substituent appears more than once, use the multiplying prefixes di-, tri-, tetra- and so on. A separate locant is used for each substituent, and the locants are separated from each other by commas and from the words by hyphens CH3CCH2CH CH3CHCHCH3 IUPAC name: 2, 2-dimethylbutane IUPAC name: 23-dimethylbutane TPROBLEM 2.6 Phytane is a naturally occurring alkane produced by the alga Spirogyra and is a constituent of petroleum. the IUPAC name for phytane is 2, 6, 10, 14-tetramethylhexadecane Write a structural formula for phytane PROBLEM 2.7 Derive the IUPAC names for (a the isomers of CaH1o (c)(CH3)3CCH2CH(CH3)2 (b)The isomers of CsH, (d)(CH3)3CC(CH3)3 Back Forward Main MenuToc Study Guide ToC Student o MHHE Website
64 CHAPTER TWO Alkanes Step 3 Number the longest continuous chain in the direction that gives the lowest number to the substituent group at the first point of branching. The numbering scheme Both schemes count five carbon atoms in their longest continuous chain and bear a methyl group as a substituent at the second carbon. An alternative numbering sequence that begins at the other end of the chain is incorrect: Step 4 Write the name of the compound. The parent alkane is the last part of the name and is preceded by the names of the substituent groups and their numerical locations (locants). Hyphens separate the locants from the words. The same sequence of four steps gives the IUPAC name for the isomer that has its methyl group attached to the middle carbon of the five-carbon chain. Both remaining C6H14 isomers have two methyl groups as substituents on a fourcarbon chain. Thus the parent chain is butane. When the same substituent appears more than once, use the multiplying prefixes di-, tri-, tetra-, and so on. A separate locant is used for each substituent, and the locants are separated from each other by commas and from the words by hyphens. PROBLEM 2.6 Phytane is a naturally occurring alkane produced by the alga Spirogyra and is a constituent of petroleum. The IUPAC name for phytane is 2,6,10,14-tetramethylhexadecane. Write a structural formula for phytane. PROBLEM 2.7 Derive the IUPAC names for (a) The isomers of C4H10 (c) (CH3)3CCH2CH(CH3)2 (b) The isomers of C5H12 (d) (CH3)3CC(CH3)3 IUPAC name: 2,2-dimethylbutane CH3CCH2CH3 W W CH3 CH3 IUPAC name: 2,3-dimethylbutane CH3CHCHCH3 W CH3 W CH3 CH IUPAC name: 3-methylpentane 3CH2CHCH2CH3 W CH3 IUPAC name: 2-methylpentane CH3CHCH2CH2CH3 W CH3 CH3CHCH2CH2CH3 W CH3 (methyl group attached to C-4) 5 43 2 1 CH3CHCH2CH2CH3 W CH3 CH3CHCH2CH2CH3 W CH3 is equivalent to 1 23 4 5 1 23 4 5 Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website