CHAPTER TWO Alkanes METHANE AND THE BIOSPHERE* ne of the things that environmental scientists the atmosphere, but most of the rest simply ends up do is to keep track of important elements in completing the carbon cycle. It exits the anaerobic the biosphere-in what form do these ele- environment where it was formed and enters the ments normally occur, to what are they transformed, aerobic world where it is eventually converted to car and how are they returned to their normal state? bon dioxide by a variety of processes Careful studies have given clear, although compli- When we consider of methane we have cated, pictures of the"nitrogen cycle, the"sulfur cy- to add" old"methane, methane that was formed carbon ge.cycle, "begins ano ycle, " for example. The millions of years ago but became trapped beneath cle, "and the"phosphorus ends with atmospheric the earth's surface, to the"new"methane just d oxide. It can be represented in an abbrevi- scribed Firedamp, an explosion hazard to miners, oc- in layers of coal and is mostly methane. Petro- leum deposits, formed by microbial decomposition of CO2+ H2o+ energy carbohydrates plant material under anaerobic conditions, are al ways accompanied by pockets of natural gas, which is respiration An interesting thing happens when trapped ubstances of methane leaks from sites under the deep ocean floor. If the pres eno h (50 atm) and th cold enough(4oC), the methane doesn't simply bub Methane is one of literally millions of com- ble to the surface. Individual methane molecules be pounds in the carbon cycle, but one of the most come trapped inside clusters of 6-18 water molecules abundant. It is formed when carbon-containing com- forming methane clathrates or methane hydrates pounds decompose in the absence of air (anaerobic Aggregates of these clathrates stay at the bottom of conditions). The organisms that bring this about are the ocean in what looks like a lump of dirty ice.Ice called methanoarchaea. Cells can be divided into that burns. Far from being mere curiosities, methane three types: archaea, bacteria, and eukarya. clathrates are potential sources of energy on a scale Methanoarchaea are one kind of archaea and may greater than that of all known oil reserves combined rank among the oldest living things on earth. They At present, it is not economically practical to extract can convert a number of carbon-containing com- the methane however pounds, including carbon dioxide and acetic acid, to Methane clathrates have received recent atten- methane tion from a different segment of the scientific com- Virtually anywhere water contacts organic mat- munity. While diving in the Gulf of Mexico in 1997, a ter in the absence of air is a suitable place for research team of biologists and environmental scien- methanoarchaea to thrive--at the bottom of ponds, tists were surprised to find a new species of worm bogs, and rice fields, for example. Marsh gas (swamp grazing on the mound of a methane clathrate.What gas) is mostly methane Methanoarchaea live inside were these worms feeding on? Methane? Bacteria termites and grass-eating animals. One source quotes that live on the methane? A host of questions having 20 L/day as the methane output of a large cow. to do with deep-ocean ecosystems suddenly The scale on which methanoarchaea churn out emerged. Stay tuned methane, estimated to be 10 1-10'2 lb/year, is enor "The biosphere is the part of the earth where life is; it includes the mous. About 10% of this amount makes its way into surface, the oceans, and the lower atmospher n-Butane and isobutane have the same molecular formula but differ in the order in which their atoms are connected. They are constitutional isomers of each other (Section 1.8). Because they are different in structure, they can have different properties. Both are gases at room temperature, but n-butane boils almost 10C higher than isobutane and has a melting point that is over 20C higher Back Forward Main MenuToc Study Guide ToC Student o MHHE Website
58 CHAPTER TWO Alkanes METHANE AND THE BIOSPHERE* One of the things that environmental scientists do is to keep track of important elements in the biosphere—in what form do these elements normally occur, to what are they transformed, and how are they returned to their normal state? Careful studies have given clear, although complicated, pictures of the “nitrogen cycle,” the “sulfur cycle,” and the “phosphorus cycle,” for example. The “carbon cycle,” begins and ends with atmospheric carbon dioxide. It can be represented in an abbreviated form as: Methane is one of literally millions of compounds in the carbon cycle, but one of the most abundant. It is formed when carbon-containing compounds decompose in the absence of air (anaerobic conditions). The organisms that bring this about are called methanoarchaea. Cells can be divided into three types: archaea, bacteria, and eukarya. Methanoarchaea are one kind of archaea and may rank among the oldest living things on earth. They can convert a number of carbon-containing compounds, including carbon dioxide and acetic acid, to methane. Virtually anywhere water contacts organic matter in the absence of air is a suitable place for methanoarchaea to thrive—at the bottom of ponds, bogs, and rice fields, for example. Marsh gas (swamp gas) is mostly methane. Methanoarchaea live inside termites and grass-eating animals. One source quotes 20 L/day as the methane output of a large cow. The scale on which methanoarchaea churn out methane, estimated to be 1011–1012 lb/year, is enormous. About 10% of this amount makes its way into CO2 H2O energy carbohydrates naturally occurring substances of numerous types photosynthesis respiration respiration the atmosphere, but most of the rest simply ends up completing the carbon cycle. It exits the anaerobic environment where it was formed and enters the aerobic world where it is eventually converted to carbon dioxide by a variety of processes. When we consider sources of methane we have to add “old” methane, methane that was formed millions of years ago but became trapped beneath the earth’s surface, to the “new” methane just described. Firedamp, an explosion hazard to miners, occurs in layers of coal and is mostly methane. Petroleum deposits, formed by microbial decomposition of plant material under anaerobic conditions, are always accompanied by pockets of natural gas, which is mostly methane. An interesting thing happens when trapped methane leaks from sites under the deep ocean floor. If the pressure is high enough (50 atm) and the water cold enough (4°C), the methane doesn’t simply bubble to the surface. Individual methane molecules become trapped inside clusters of 6–18 water molecules forming methane clathrates or methane hydrates. Aggregates of these clathrates stay at the bottom of the ocean in what looks like a lump of dirty ice. Ice that burns. Far from being mere curiosities, methane clathrates are potential sources of energy on a scale greater than that of all known oil reserves combined. At present, it is not economically practical to extract the methane, however. Methane clathrates have received recent attention from a different segment of the scientific community. While diving in the Gulf of Mexico in 1997, a research team of biologists and environmental scientists were surprised to find a new species of worm grazing on the mound of a methane clathrate. What were these worms feeding on? Methane? Bacteria that live on the methane? A host of questions having to do with deep-ocean ecosystems suddenly emerged. Stay tuned. *The biosphere is the part of the earth where life is; it includes the surface, the oceans, and the lower atmosphere. n-Butane and isobutane have the same molecular formula but differ in the order in which their atoms are connected. They are constitutional isomers of each other (Section 1.8). Because they are different in structure, they can have different properties. Both are gases at room temperature, but n-butane boils almost 10°C higher than isobutane and has a melting point that is over 20°C higher. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
2.6 Higher n-Alkanes The bonding in n-butane and isobutane continues the theme begun with methane ethane, and propane. All of the carbon atoms are sp-hybridized, all of the bonds are o about 5% n-butane and 95% bonds, and the bond angles at carbon are close to tetrahedral. This generalization holds isobutane in a sealed con- for all alkanes regardless of the number of carbons they have duced by the two compounds 2.6 HIGHER n-ALKANES eep them in the n-Alkanes are alkanes that have an unbranched carbon chain n-Pentane and n-hexane emits a fine stream of the va. prized mixture across a are n-alkanes possessing five and six carbon atoms, respectively k which ignites it. CH3CH, CH,CH, CH3 CH;CH, CH,CH,,CH I-Hexane Their condensed structural formulas can be abbreviated even more by indicating within parentheses the number of methylene groups in the chain. Thus, n-pentane may be writ- ten as CH3 (CH2)3 CH3 and n-hexane as CH3(CH2)4CH3. This shortcut is especially con- venient with longer-chain alkanes. The laboratory synthesis of the"ultralong "alkane CH3(CH2)388 CH3 was achieved in 1985; imagine trying to write a structural formula for this compound in anything other than an abbreviated way! PROBLEM 2.2 An n-alkane of molecular formula C28Hs has been isolated from a certain fossil plant. Write a condensed structural formula for this alkane. n-Alkanes have the general formula CH3(CH2),CH3 and are said to belong to a homologous series of compounds. A homologous series is one in which successive mem- bers differ by a-CH2- group Unbranched alkanes are sometimes referred to as"straight-chain alkanes but, as we'lI see in Chapter 3, their chains are not straight but instead tend to adopt the"zigzag shape portrayed in the bond-line formulas introduced in Section 1.7. Bond-line formula of n-hexane PROBLEM 2.3 Much of the communication between insects involves chemical messengers called pheromones. A species of cockroach secretes a substance from its mandibular glands that alerts other cockroaches to its presence and causes them to congregate. One of the principal components of this aggregation hermone is the alkane shown in the bond-line formula that follows Give the molecular formula of this substance and represent it by a condensed formula 2.7 THE CsH, ISOMERS Three isomeric alkanes have the molecular formula CsHiz. The unbranched isomer is, as we have seen, n-pentane. The isomer with a single methyl branch is called isopen- tane. The third isomer has a three-carbon chain with two methyl branches. It is called n-Pentane: CH: CH,CH? CH2 CH3 or CH=(CH?)3CH3 or (CH3) CHCH,CH3 or Make molecular models pentane: CH: CHCH,CH of the th mers of CsH12. CH Back Forward Main MenuToc Study Guide ToC Student o MHHE Website
The bonding in n-butane and isobutane continues the theme begun with methane, ethane, and propane. All of the carbon atoms are sp3 -hybridized, all of the bonds are bonds, and the bond angles at carbon are close to tetrahedral. This generalization holds for all alkanes regardless of the number of carbons they have. 2.6 HIGHER n-ALKANES n-Alkanes are alkanes that have an unbranched carbon chain. n-Pentane and n-hexane are n-alkanes possessing five and six carbon atoms, respectively. Their condensed structural formulas can be abbreviated even more by indicating within parentheses the number of methylene groups in the chain. Thus, n-pentane may be written as CH3(CH2)3CH3 and n-hexane as CH3(CH2)4CH3. This shortcut is especially convenient with longer-chain alkanes. The laboratory synthesis of the “ultralong” alkane CH3(CH2)388CH3 was achieved in 1985; imagine trying to write a structural formula for this compound in anything other than an abbreviated way! PROBLEM 2.2 An n-alkane of molecular formula C28H58 has been isolated from a certain fossil plant. Write a condensed structural formula for this alkane. n-Alkanes have the general formula CH3(CH2)xCH3 and are said to belong to a homologous series of compounds. A homologous series is one in which successive members differ by a ±CH2± group. Unbranched alkanes are sometimes referred to as “straight-chain alkanes,” but, as we’ll see in Chapter 3, their chains are not straight but instead tend to adopt the “zigzag” shape portrayed in the bond-line formulas introduced in Section 1.7. PROBLEM 2.3 Much of the communication between insects involves chemical messengers called pheromones. A species of cockroach secretes a substance from its mandibular glands that alerts other cockroaches to its presence and causes them to congregate. One of the principal components of this aggregation pheromone is the alkane shown in the bond-line formula that follows. Give the molecular formula of this substance, and represent it by a condensed formula. 2.7 THE C5H12 ISOMERS Three isomeric alkanes have the molecular formula C5H12. The unbranched isomer is, as we have seen, n-pentane. The isomer with a single methyl branch is called isopentane. The third isomer has a three-carbon chain with two methyl branches. It is called neopentane. CH3CHCH2CH3 CH3 n-Pentane: Isopentane: CH3CH2CH2CH2CH3 or or CH3(CH2)3CH3 (CH3)2CHCH2CH3 or or Bond-line formula of n-pentane Bond-line formula of n-hexane CH3CH2CH2CH2CH3 n-Pentane CH3CH2CH2CH2CH2CH3 n-Hexane 2.6 Higher n-Alkanes 59 “Butane” lighters contain about 5% n-butane and 95% isobutane in a sealed container. The pressure produced by the two compounds (about 3 atm) is enough to keep them in the liquid state until opening a small valve emits a fine stream of the vaporized mixture across a spark which ignites it. Make molecular models of the three isomers of C5H12. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
CHAPTER TWO Alkanes CH3 Neopentane: CH3CCH (CH3)C he number of C,H2n+z iso. Table 2.3 presents the number of possible alkane isomers as a function of the num- mers has been calculated for ber of carbon atoms they contain. As the table shows, the number of isomers increases alues of n from 1 to 40 enormously with the number of carbon atoms and raises two important questions and the comment ma l. How can we tell when we have written all the possible isomers corresponding to C157H33s exceeds the number a particular molecular formula? niverse(10). These obser 2. How can we name alkanes so that each one has a unique name? ations and the historical The answer to the first question is that you cannot easily calculate the number of April 1989 issue of isomers. The data in Table 2.3 were determined by a mathematician who concluded that the Journal of Chemical Edu- there was no simple expression from which to calculate the number of isomers. The best cation(pp. 278-281). way to ensure that you have written all the isomers of a particular molecular formula is to work systematically, beginning with the unbranched chain and then shortening it while dding branches one by one. It is essential that you be able to recognize when two different looking structural formulas are actually the same molecule written in different ways. The key point is the connectivity of the carbon chain. For example, the following group of struc tural formulas do not represent different compounds; they are just a portion of the many ways we could write a structural formula for isopentane. Each one has a continuous chain of four carbons with a methyl branch located one carbon from the end of the chain CH The fact that all of these CH3,CI CH3CHCH2CH3 CH3 CHCHCH3 ame substance can be clearly CH3 CH3CH,CHCH3 CHCH, CH3 H3 TABLE 2. 3 The Number of Constitutionally Isomeric Alkanes of Particular Molecular formulas Molecular formula Number of constitutional isomers CHa CaH 1235 C6H14 C7H16 cC 855 15n32 4,347 366,319 62491,178805831 Back Forward Main MenuToc Study Guide ToC Student o MHHE Website
60 CHAPTER TWO Alkanes Table 2.3 presents the number of possible alkane isomers as a function of the number of carbon atoms they contain. As the table shows, the number of isomers increases enormously with the number of carbon atoms and raises two important questions: 1. How can we tell when we have written all the possible isomers corresponding to a particular molecular formula? 2. How can we name alkanes so that each one has a unique name? The answer to the first question is that you cannot easily calculate the number of isomers. The data in Table 2.3 were determined by a mathematician who concluded that there was no simple expression from which to calculate the number of isomers. The best way to ensure that you have written all the isomers of a particular molecular formula is to work systematically, beginning with the unbranched chain and then shortening it while adding branches one by one. It is essential that you be able to recognize when two differentlooking structural formulas are actually the same molecule written in different ways. The key point is the connectivity of the carbon chain. For example, the following group of structural formulas do not represent different compounds; they are just a portion of the many ways we could write a structural formula for isopentane. Each one has a continuous chain of four carbons with a methyl branch located one carbon from the end of the chain. CH3CHCH2CH3 W CH3 CH3CHCH2CH3 W CH3 CH3CH2CHCH3 W CH3 CH3CH2CHCH3 W CH3 CHCH2CH3 W W CH3 CH3 CH3 CH3CCH3 CH3 Neopentane: or (CH3)4C or TABLE 2.3 The Number of Constitutionally Isomeric Alkanes of Particular Molecular Formulas Molecular formula CH4 C2H6 C3H8 C4H10 C5H12 C6H14 C7H16 C8H18 C9H20 C10H22 C15H32 C20H42 C40H82 Number of constitutional isomers 1 1 1 2 3 5 9 18 35 75 4,347 366,319 62,491,178,805,831 The number of CnH2n2 isomers has been calculated for values of n from 1 to 400 and the comment made that the number of isomers of C167H336 exceeds the number of particles in the known universe (1080 ). These observations and the historical background of isomer calculation are described in a paper in the April 1989 issue of the Journal of Chemical Education (pp. 278–281). The fact that all of these structural formulas represent the same substance can be clearly seen by making molecular models. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
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 Website
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 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 written 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. Conversely, 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 systematic. 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 system 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 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. 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 condensed 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 Centennial of Systematic Organic Nomenclature” in the November 1992 issue of the Journal of Chemical Education (pp. 863–865). Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website
CHAPTER TWO Alkanes TABLE 2.4 IUPAC Names of Unbranched Alkanes Number Number Number of carbon of carbon Name of carbon Name Methane Undecane Henicosane Ethane 123456789 Dodecane 1234012 Docosane 23456 3 Propane Tridecane Tricosane Butane Tetradecane Tetracosane Pentane Pentadecane Triacontane Hexane Hexadecane Hentriacontane Heptane Heptadecane Dotriacontane 8 Octane Octadecane Tetracontane Nonane Nonadecane 60 Pentacontane Decane Icosane 100 Hectare Spelled"eicosane"prior to 1979 version of IUPAC rules. (c)What is the IUPAC name of the alkane described in Problem 2.3 as a compo- nent of the cockroach aggregation pheromone? SAMPLE SoLUTION(a) Note in Table 2.4 that hentriacontane has 31 carbon atoms. All the alkanes in Table 2,4 have unbranched carbon chains. Hentriacon tane has the condensed structural formula CH3(CH2)29CH3 In Problem 2. 4 you were asked to write structural formulas for the five alkanes of molecular formula C6Hi4. In the next section you will see how the IUPAC rules generate a unique name for each isomer 2.9 APPLYING THE IUPAC RULES: THE NAMES OF THE C6H14 ISOMERS We can present and illustrate the most important of the IUPAC rules for alkane nomen You might find it helpful clature by naming the five C6Hi4 isomers. By definition (Table 2.4), the unbranc C6H14 isomer is the ChIa isomers CH3CH, CH,CH, CH,CH3 IUPAC name: hexane The IUPAC rules name branched alkanes as substituted derivatives of the unbranched alkanes listed in Table 2. 4. Consider the C6H14 isomer represented by the structure CH3CHCH, CH,CH Step I Pick out the longest continuous carbon chain, and find the IupAc name in Table 2.4 that corresponds to the unbranched alkane having that number of carbons. This is the parent alkane from which the IUPAC name is to be derived. Back Forward Main MenuToc Study Guide ToC Student o MHHE Website
62 CHAPTER TWO Alkanes (c) What is the IUPAC name of the alkane described in Problem 2.3 as a component of the cockroach aggregation pheromone? SAMPLE SOLUTION (a) Note in Table 2.4 that hentriacontane has 31 carbon atoms. All the alkanes in Table 2.4 have unbranched carbon chains. Hentriacontane has the condensed structural formula CH3(CH2)29CH3. In Problem 2.4 you were asked to write structural formulas for the five isomeric alkanes of molecular formula C6H14. In the next section you will see how the IUPAC rules generate a unique name for each isomer. 2.9 APPLYING THE IUPAC RULES: THE NAMES OF THE C6H14 ISOMERS We can present and illustrate the most important of the IUPAC rules for alkane nomenclature by naming the five C6H14 isomers. By definition (Table 2.4), the unbranched C6H14 isomer is hexane. The IUPAC rules name branched alkanes as substituted derivatives of the unbranched alkanes listed in Table 2.4. Consider the C6H14 isomer represented by the structure Step 1 Pick out the longest continuous carbon chain, and find the IUPAC name in Table 2.4 that corresponds to the unbranched alkane having that number of carbons. This is the parent alkane from which the IUPAC name is to be derived. CH3CHCH2CH2CH3 W CH3 CH3CH2CH2CH2CH2CH3 IUPAC name: hexane (common name: n-hexane) TABLE 2.4 IUPAC Names of Unbranched Alkanes Number of carbon atoms 1 2 3 4 5 6 7 8 9 10 Name Methane Ethane Propane Butane Pentane Hexane Heptane Octane Nonane Decane Name Undecane Dodecane Tridecane Tetradecane Pentadecane Hexadecane Heptadecane Octadecane Nonadecane Icosane* Number of carbon atoms 11 12 13 14 15 16 17 18 19 20 Name Henicosane Docosane Tricosane Tetracosane Triacontane Hentriacontane Dotriacontane Tetracontane Pentacontane Hectane Number of carbon atoms 21 22 23 24 30 31 32 40 50 100 *Spelled “eicosane” prior to 1979 version of IUPAC rules. You might find it helpful to make molecular models of all the C6H14 isomers. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website