1026 CHAPTER TWENTY-SIX Lipids Myrcene, a hydrocarbon isolated from bayberry oil, is a typical terpene CH (CH3)C=CHCH,CH, CCH=,= The structural feature that distinguishes terpenes from other natural products is the iso- prene unit. The carbon skeleton of myrcene(exclusive of its double bonds) corresponds to the head-to-tail union of two isoprene units CH CH=CH,≡∠ Two isoprene units (2-methyl-1, 3-butadiene) linked head to tail Terpenes are often referred to as isoprenoid compounds. They are classified according to the number of carbon atoms they contain, as summarized in Table 26.2 pounds. Although the term"terpene"once referred only to hydrocarbons, current usage includes functionally substituted derivatives as well. Figure 26.6 presents the structural formulas for a number of representative terpenes. The isoprene units in some of these are relatively easy to identify. The three isoprene units in the sesquiterpene farnesol, for example, are indicated as follows in color. They are joined in a head-to-tail fashion Many terpenes contain one or more rings, but these also can be viewed as collec- tions of isoprene units. An example is a-selinene. Like farnesol, it is made up of three isoprene units linked head to tail TABLE 26.2 Classification of Terpenes Class Number of carbon atoms Monoterpene sesquiterpene Diterpene 05050 ne Tetraterpene Back Forward Main MenuToc Study Guide ToC Student o MHHE Website1026 CHAPTER TWENTY-SIX Lipids Myrcene, a hydrocarbon isolated from bayberry oil, is a typical terpene: The structural feature that distinguishes terpenes from other natural products is the iso￾prene unit. The carbon skeleton of myrcene (exclusive of its double bonds) corresponds to the head-to-tail union of two isoprene units. Terpenes are often referred to as isoprenoid compounds. They are classified according to the number of carbon atoms they contain, as summarized in Table 26.2. Although the term “terpene” once referred only to hydrocarbons, current usage includes functionally substituted derivatives as well. Figure 26.6 presents the structural formulas for a number of representative terpenes. The isoprene units in some of these are relatively easy to identify. The three isoprene units in the sesquiterpene farnesol, for example, are indicated as follows in color. They are joined in a head-to-tail fashion. Many terpenes contain one or more rings, but these also can be viewed as collec￾tions of isoprene units. An example is -selinene. Like farnesol, it is made up of three isoprene units linked head to tail. CH3 CH2 CH2 H3C Isoprene units in -selinene OH Isoprene units in farnesol CH2 C CH3 CH CH2 Isoprene (2-methyl-1,3-butadiene) head tail Two isoprene units linked head to tail Myrcene (CH3)2C CH2 CHCH2CH2CCH CH2 TABLE 26.2 Classification of Terpenes Class Monoterpene Sesquiterpene Diterpene Sesterpene Triterpene Tetraterpene Number of carbon atoms 10 15 20 25 30 40 There are more than 23,000 known isoprenoid com￾pounds. Back Forward Main Menu TOC Study Guide TOC Student OLC MHHE Website