2.8 IUPAC Nomenclature of unbranched alkanes PROBLEM 2. 4 Write condensed and bond-line formulas for the five isomeric C6H14 alkanes. SAMPLE SOLUTION When writing isomeric alkanes, it is best to begin with the CHa CH2 CH2CI Next, remove a carbon from the chain and use it as a one-carbon(methyl)branch at the carbon atom next to the end of the chain CH3CHCH2 CH2 CH3 or Now, write structural formulas for the remaining three isomers. Be sure that each one is a unique compound and not simply a different representation of one writ- ten previously. The answer to the second question--how to provide a name that is unique to a particular structure--is presented in the following section. It is worth noting, however, that being able to name compounds in a systematic way is a great help in deciding whether two structural formulas represent isomeric substances or are the same compound represented in two different ways. By following a precise set of rules, one will always get the same systematic name for a compound, regardless of how it is written. Con versely, two different compounds will always have different names. 2.8 IUPAC NOMENCLATURE OF UNBRANCHED ALKANES Nomenclature in organic chemistry is of two types: common(or""trivial")and system atic. Some common names existed long before organic chemistry became an organized branch of chemical science. Methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, and neopentane are common names. One simply memorizes the name that goes with a compound in just the same way that one matches names with faces. So long as there are only a few names and a few compounds, the task is manageable. But there are millions of organic compounds already known, and the list continues to grow! A sys- tem built on common names is not adequate to the task of communicating structural information. Beginning in 1892, chemists developed a set of rules for naming organic compounds based on their structures, which we now call the IUPAC rules, in which IUPAC stands for the"International Union of Pure and Applied Chemistry. " (See the accompanying box, "A Brief History of Systematic Organic Nomenclature.) A more detailed account of The IUPAC rules assign names to unbranched alkanes as shown in Table 2. 4. nomenclature may be found Methane, ethane, propane, and butane are retained for CH4, CH3 CH3, CH3CH2CH3, and in the article"The Centen- CH3 CH2 CH2CH3, respectively. Thereafter, the number of carbon atoms in the chain is Nomenclature"in the n specified by a Latin or Greek prefix preceding the suffix -ane, which identifies the com- vember 1992 issue of the pound as a member of the alkane family. Notice that the prefix n- is not part of the Journal of chemical Educa- IUPAC system. The IuPAC name for CH3 CH2CH2CH3 is butane, not n-butane. PROBLEM 2.5 Refer to Table 2.4 as needed to answer the following questions (a) Beeswax contains 8-9% hentriacontane write a condensed structural formula for hentriacontane (b)Octacosane has been found to be present in a certain fossil plant. write a con- densed structural formula for octacosane Back Forward Main MenuToc Study Guide ToC Student o MHHE WebsitePROBLEM 2.4 Write condensed and bond-line formulas for the five isomeric C6H14 alkanes. SAMPLE SOLUTION When writing isomeric alkanes, it is best to begin with the unbranched isomer. Next, remove a carbon from the chain and use it as a one-carbon (methyl) branch at the carbon atom next to the end of the chain. Now, write structural formulas for the remaining three isomers. Be sure that each one is a unique compound and not simply a different representation of one writ￾ten previously. The answer to the second question—how to provide a name that is unique to a particular structure—is presented in the following section. It is worth noting, however, that being able to name compounds in a systematic way is a great help in deciding whether two structural formulas represent isomeric substances or are the same compound represented in two different ways. By following a precise set of rules, one will always get the same systematic name for a compound, regardless of how it is written. Con￾versely, two different compounds will always have different names. 2.8 IUPAC NOMENCLATURE OF UNBRANCHED ALKANES Nomenclature in organic chemistry is of two types: common (or “trivial”) and system￾atic. Some common names existed long before organic chemistry became an organized branch of chemical science. Methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, and neopentane are common names. One simply memorizes the name that goes with a compound in just the same way that one matches names with faces. So long as there are only a few names and a few compounds, the task is manageable. But there are millions of organic compounds already known, and the list continues to grow! A sys￾tem built on common names is not adequate to the task of communicating structural information. Beginning in 1892, chemists developed a set of rules for naming organic compounds based on their structures, which we now call the IUPAC rules, in which IUPAC stands for the “International Union of Pure and Applied Chemistry.” (See the accompanying box, “A Brief History of Systematic Organic Nomenclature.”) The IUPAC rules assign names to unbranched alkanes as shown in Table 2.4. 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 com￾pound 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. PROBLEM 2.5 Refer to Table 2.4 as needed to answer the following questions: (a) Beeswax contains 8–9% hentriacontane. Write a condensed structural formula for hentriacontane. (b) Octacosane has been found to be present in a certain fossil plant. Write a con￾densed structural formula for octacosane. CH3CHCH2CH2CH3 or CH3 CH3CH2CH2CH2CH2CH3 or 2.8 IUPAC Nomenclature of Unbranched Alkanes 61 A more detailed account of the history of organic nomenclature may be found in the article “The Centen￾nial of Systematic Organic Nomenclature” in the No￾vember 1992 issue of the Journal of Chemical Educa￾tion (pp. 863–865). Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website