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 WebsiteThe 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 writ￾ten as CH3(CH2)3CH3 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)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 mem￾bers 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 isopen￾tane. 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 con￾tainer. The pressure pro￾duced 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 va￾porized mixture across a spark which ignites it. Make molecular models of the three isomers of C5H12. 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