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634 20 Organic Chemistry ""'""- C_ti_Q~ter Key Terms organic chemistry (p. 595) biomolecules (p. 596) hydrocarbon (20.2) alkane (20.2) normal (straight-chain or unbranched) hydrocarbons (20.2) structural isomerism (20.3) combustion reaction (20.6) substitution reaction (20.6) dehydrogenation reaction (20.6) alkene (20.7) alkyne (20.7) addition reaction (20.7) hydrogenation reaction (20.7) halogenation (20.7) polymerization (20.7) aromatic hydrocarbon (20.8) phenyl group (20.9) hydrocarbon derivative (20.10) functional group (20.10) alcohol (20.11) phenol (20.12) ketone (20.13) aldehyde (20.13) carboxylic acid (20.15) ester (20.15) polymer (20.16) addition polymerization (20.16) condensation polymerization (20.16) summary 1. The study of carbon-containing compounds and their properties is called organic chemistry. Most organic compounds contain chains or rings of carbon atoms. The organic molecules responsible for maintaining and reproducing life are called biomolecules. 2. Hydrocarbons are organic compounds composed of carbon and hydrogen. Those that contain only C-C single bonds are saturated and are called alkanes, and those with carbon-carbon multiple bonds are unsaturated. Unsaturated hydrocarbons can become saturated by the addition of hydrogen, halogens, and/or other substituents. 3. All alkanes can be represented by the general formula C Il H 2n + 2. Methane, CH 4, is the simplest alkane, and the next three in the series are ethane, C2 H 6 ; propane, C3H g ; Review and butane, C4HIO. In a saturated hydrocarbon, each carbon atom is bonded to four other atoms. Alkanes containing long chains of carbon atoms are called normal, or straight-chain, hydrocarbons. 4. Stmctural isomerism in alkanes involves the formation of branched structures. Specific mles for systematically naming alkanes indicate the point of attachment of any substituent group, the length of the root chain, and so on. 5. Alkanes can undergo combustion reactions to form carbon dioxide and water or substitution reactions in which hydrogen atoms are replaced by other atoms. Alkanes can also undergo dehydrogenation to form unsaturated hydrocarbons. 6. Hydrocarbons with carbon-carbon double bonds are called alkenes. The simplest alkene is ethylene, C2H4. Alkynes are unsaturated hydrocarbons with a carboncarbon triple bond. The simplest in the series is acetylene, C2H2 . 7. Unsaturated hydrocarbons undergo addition reactions such as hydrogenation (addition of hydrogen atoms) and halogenation (addition of halogen atoms). Ethylene and substituted ethylene molecules can undergo polymerization, a process by which many molecules (monomers) are joined together to form a large chain-like molecule. 8. Organic molecules that contain elements in addition to carbon and hydrogen can be viewed as hydrocarbon derivatives: hydrocarbons with functional groups. Each functional group exhibits characteristic chemical properties. 9. Alcohols contain the -OH functional group. Aldehydes and ketones contain the carbonyl functional group, "c=o / In aldehydes this group is bonded to at least one hydrogen atom. Carboxylic acids are characterized by the carboxyl functional group, -1'0 -C "OH They can react with alcohols to form esters. 10. Polymers can be formed by addition polymerization, in which monomers add together, or by condensation polymerization, which involves the splitting out of small molecules (such as water) as the monomers react. Questions and Problems Questions and Problems All even-numbered exercises have answers in the back of this book and solutions in the Solutions Guide. 20.1 • Carbon Bonding QUESTIONS 1. What makes carbon able to form so many different compounds? 2. What is the maximum number of other atoms to which a given carbon atom can be attached? Why? --3. What does a double bond represent? Give two examples of molecules in which double bonds occur, and draw the Lewis structures of those molecules. 4. What does a triple bond represent? How many pairs of electrons are shared between the atoms in a triple bond? Draw the Lewis structure of a molecule with a triple bond. 5. When a carbon atom is bonded to four other atoms, what geometric arrangement occurs around the carbon atom? Why? 6. The structures of the organic molecules propane and butane are given in Figure 20.3. How many other atoms is each carbon bonded to in these molecules? What is the geometry around each carbon atom in these molecules? 635 PROBLEMS 11. Write structural formulas for the normal (straight-chain) alkanes with: a. eleven carbon atoms c. twenty carbon atoms b. fifteen carbon atoms 12. Write structural formulas for the normal (straight-chain) alkanes with: a. eight carbon atoms c. twelve carbon atoms b. ten carbon atoms 13. For each of the following straight-chain alkanes, draw the structural formula. c. propane a. heptane d. decane b. nonane 14. Draw the structural formula for each of the following straight-chain alkanes. c. pentane a. butane b. octane d. hexane 20.3 • Structural Formulas and Isomerism QUESTIONS 15. What are structural isomers? Which is the smallest alkane that has a structural isomer? Draw structures to illustrate the isomers. 16. What is a small chain of carbon atoms called when it is attached to a longer chain of carbon atoms? ---- PROBLEMS 20.2 • Alkanes QUESTIONS 7. What does it mean to say that a hydrocarbon is saturated? To how many other atoms is each carbon atom in a saturated hydrocarbon bonded? What name is given to the family of saturated hydrocarbons? 17. Draw structural formulas for at least five isomeric alkanes having the formula C7H 16. 18. Draw the structural formulas for at least five isomeric alkanes having the formula CSH IS ' ---- 20.4 • Naming Alkanes 8. What is an unsaturated hydrocarbon? In what respect is such a hydrocarbon "unsaturated"? What structural feature characterizes unsaturated hydrocarbons? QUESTIONS 19. Give the root names for the alkanes with five through ten carbon atoms. 9. Although alkanes in which the carbon atoms form long, unbranched chains are often called "straight-chain" alkanes, why is such a chain not really straight? What is the bond angle between carbon atoms in a straight-chain alkane? 20. To what does the root name for a branched hydrocarbon correspond? 10. Write the names and structural formulas of the first ten straight-chain alkanes without looking at your textbook. By what group of atoms does each successive member of this family differ from the previous member? --- ---- 21. What is an alkyl group? How is a given alkyl group related to its parent alkane? 22. How is the position of substituents along the longest chain of a hydrocarbon indicated? ---23. How is the number of multiple substituents of the same type indicated in the systematic name of a hydrocarbon? 636 20 Organic Chemistry 24. In giving the name of a hydrocarbon with several substituents, in what order do we list the substituents? PROBLEMS 25. Give the systematic name for each of the following alkanes. CH3 a. CH3 c. . CH 3 CH 3 CH 3 CH 3 CH 3 20.5 • Petroleum 29. What are the major constituents of crude petroleum? What is the major constituent of natural gas? How were these mixtures formed? b. ?Hz-CHz-CHz-?H-CHz-CHz-?Hz CH 3 3-methylpentane 4-tert-butylheptane 5-propylnonane 2,4,6,9-tetramethyldecane QUESTIONS I CH 3-C-CHz-CH-CHz-CH3 I I CH 3 a. b. c. d. . CH 3 I I CH 3 -C-CHz-C-CH3 I I 30. List several petroleum fractions and tell how each fraction is primarily used. --31. What is pyrolytic cracking, and why is the process applied to the kerosene fraction of petroleum? 32. Why was tetraethyl lead, (CZHS)4Pb, added to gasoline in the past? Why is the use of this substance being phased out? 20.6 • Reactions of Alkanes QUESTIONS 26. Give the systematic name for each of the following alkanes. 33. Explain why alkanes are relatively unreactive. 34. What is a combustion reaction? How have we made use of the combustion reactions of alkanes? 35. What is a substitution reaction? Give an example of a reactive molecule that is able to replace the hydrogen atoms of an alkane. 36. What is a dehydrogenation reaction? What results when an alkane is dehydrogenated? PROBLEMS 37. Complete and balance each of the following chemical equations that represent combustion reactions. a. C3H 8(g) + Oz(g) -t b. CSH1Z(I) + Oz(g) -t c. C7H 16(l) + Oz(g) -t 27. Draw a structural formula for each of the following compounds. a. 2-methylheptane b. 3-methylheptane c. 4-methylheptane d. 2,2-dimethylheptane e. 2,4-dimethylheptane 28. Draw the structural formula for each of the following compounds. 38. Complete and balance each of the following chemical equations. a. CZH 6(g) + 02(g) -t ? + ? b. CHzClz(l) + Clz(g) -t HCI(g) + ? c. CHz=CH-CHz-CH3(l) + Brz(l) -t ? 20.7 • Alkenes and Alkynes QUESTIONS 39. What is an alkene? What structural feature characterizes alkenes? Give the general formula for alkenes. Questions and Problems 40. What is an alkyne? What structural feature characterizes alkynes? Give the general formula for alkynes. --- 41. How is the root name of an alkane modified to indicate that a given hydrocarbon contains a double or triple bond in its longest continuous chain? 42. How is the location of a double or triple bond in the longest continuous chain of an unsaturated hydrocarbon indicated? 43. Describe some addition reactions that unsaturated hydrocarbons undergo. Give the specific name of the type of addition process, and indicate what atoms are added to the double or triple bond. 44. How is a liquid fat, such as com oil, converted into a solid form for use as a table spread or shortening? PROBLEMS 45. Give the systematic name for each of the following unsaturated hydrocarbons and substituted unsaturated compounds. a. CH3-CH=CH-CH3 b. CH3- H-CH=CH 2 T CH 3 c. CH-C-CH2-CH3 d. CH2=CH-CH-CH3 I CI 46. Give the systematic name for each of the following unsaturated hydrocarbons. a. CH=C-CH3 b. CH3-CH2-C C-CH2-CH3 c. CH3-CH2-CH=CH-CH2-CH3 --- 47. Draw structural formulas for at least four isomeric hydrocarbons containing eight carbon atoms and one double bond. 48. Draw structural formulas showing all possible molecules containing six carbon atoms and having one triple bond. 20.9 • Naming Aromatic Compounds QUESTIONS 51. How is a monosubstituted benzene named? Give the structures and names of two examples. Also give two examples of monosubstituted benzenes that have special names. 52. How is the benzene ring named if it is considered a substituent in another molecule? Give the structures and names of two examples. --53. If a benzene ring contains several substituents, how are the relative locations of the substituents numbered in the systematic name given to the molecule? 54. What do the prefixes ortho-, meta-, and para- refer to in terms of the relative location of substituents in a disubstituted benzene? PROBLEMS 55. Draw a structural formula for each of the following aromatic or substituted aromatic compounds. a. 3-bromochlorobenzene b. I A-dichlorobenzene c. 4-bromo-I-methylbenzene (4-bromotoluene) d. naphthalene e. I A-dimethylbenzene 56. Name each of the following aromatic or substituted aromatic compounds. a. O=CH 3 CH 3 b. CI CI*CI CI CI CI '000 20.8 • Aromatic Hydrocarbons QUESTIONS 49. What structure do all aromatic hydrocarbons have in common? 50. Benzene exhibits resonance. Explain this statement in terms of the different Lewis structures that can be drawn for benzene. 637 "CIOO 638 20 Organic Chemistry 20.10 • Functional Groups PROBLEMS 57. On the basis of the functional groups listed in Table 20.5, identify the family of organic compounds to which each of the following belongs. a. CH3-CH2-CH-CH2-CH3 I OH b. CH 3-CH2- 20.12 • Properties and Uses of Alcohols =O r H QUESTIONS c. CH3-CH2-CH2-CH2-r=O CH2-CH2-CH3 d. CH3-CH-NH2 I CH 3 58. On the basis of the functional groups listed in Table 20.5, identify the family of organic compounds to which each of the following belongs. a. CH3CH2-0-CH2CH2CH3 b. CH3CH 2CH2CH 2-OH c. CH3CH 2CHCH3 I OH d. CH3CH2CH 2CH2COOH 63. Why is methanol sometimes called wood alcohol? Describe the modern synthesis of methanol. What are some uses of methanol? 64. Write the equation for the fermentation of glucose to form ethanol. Why can't ethanol solutions of greater than about 13% concentration be made directly by fermentation? How can the ethanol content be increased beyond this level in beverages? --65. Write the equation for the synthesis of ethanol from ethylene. What are some commercial uses of ethanol made by this process? 66. Give the names and structural formulas of two other commercially important alcohols. Cite the major use of each. --- 20.13 • Aldehydes and Ketones QUESTIONS 20.11 • Alcohols 67. What functional group is common to both aldehydes and ketones? QUESTIONS 59. What functional group characterizes an alcohol? What ending is added to the name of the parent hydrocarbon to show that a molecule is an alcohol? 60. Distinguish among primary, secondary, and tertiary alcohols. Give a structural formula for an example of each type. PROBLEMS 61. Give the systematic name for each of the following alcohols. Indicate whether the alcohol is primary, secondary, or tertiary. a. CH3CH2CH2CH2CH2-0H b. CH 3 I CH3CCH2CH3 I OH c. CH3CH2CHCH?CH3 I 62. Draw structural formulas for each of the following alcohols. Indicate whether the alcohol is primary, secondary, or tertiary. a. I-propanol b. 2-pentanol c. 2-methyl-l-propanol d. 3-methyl-3-pentanol ---- - OH d. CH3CH2CH2-OH 68. What structural feature distinguishes aldehydes from ketones? 69. Mention some commercial uses of specific aldehydes and ketones. 70. How are aldehydes and ketones most often produced commercially? Write an equation as an example of each process. 20.14. Naming Aldehydes and Ketones QUESTIONS 71. What ending is added to the root name of the parent hydrocarbon to indicate that the molecule contains the aldehyde functional group? What systematic ending is used to show that a molecule is a ketone? 72. Describe the alternative system for naming ketones. Give two examples of ketones, along with their names in both systems. Questions and Problems 73. Give the systematic name for each of the following: c. CH3 I a. CH 3-CHz-CHz-C=O CH 3-C-CH3 I I CHz-CH3 Cl c. I Cl 79. Draw the general structural formula for an ester. From what two families of organic compounds are esters synthesized? I H 80. Draw the structure of acetylsalicylic acid, and circle the portion of the molecule that shows that it is an ester. From what acid and alcohol is acetylsalicylic acid synthesized? ---- CH3 I CH3-CH-CH-CHz -C=O I I CH 3 oxidation ----'> OH b. CH3-CH-CH-C=O I 639 H PROBLEMS d. CH3 81. Give the systematic name for each of the following: I CH3-CH-C=O a. CH 3- I H e. H-CH z-COOH CH 3 CH3-CH26° b. Ol-COOH c. CH 374. Draw a structural formula for each of the following: a. ethyl phenyl ketone b. diethylketone c. 3-pentanone d. 2-chloropropanal e. 2,3-dimethylpentanal 20.15 • r Carboxylic Acids and Esters QUESTIONS 75. Draw the structure of the group that characterizes organic (carboxylic) acids. Give the general condensed formula for an organic acid. 76. Are carboxylic acids typically strong acids or weak acids? Write an equation showing the acid CH3CH zCOOH ionizing in water. --77. What systematic ending is used to show that a molecule is a carboxylic acid? Give an example. 78. Draw the structure of the principal organic product of each of the following reactions. r H-COOH OH d. CH 3 I CH 3-CHz-CH-CH-CHz-COOH I CH 3 82. Draw a structural formula for each of the following: a. ethyl butanoate b. 4-chloro-2-hydroxybenzoic acid c. methyl pentanoate d. propyl benzoate e. 2,3-dimethylbutanoic acid ---- 20.16 • Polymers QUESTIONS 83. What, in general terms, is a polymer? What is a monomer? 84. What is addition polymerization? Give an example of a common addition polymer. --- 85. What is condensation polymerization, and how does it differ from addition polymerization? Give an example of a common condensation polymer. OXIdatIOn 86. What is a polyester? What structural feature characterizes polyesters? Give an example of a common polyester. b. CH 3-CHz-?H-CH3 OH oxidation -> PROBLEMS 87. Draw the structures of acrylonitrile and butadiene. Also draw the structures of the basic repeating units when each 640 20 Organic Chemistry of these substances polymerizes. Give several uses of each polymeric substance. other atoms attach themselves to the carbon atoms of the double or triple bond. 88. For the polymeric substances nylon and Dacron, sketch representations of the repeating unit in each. 102. Unsaturated fats may be converted to saturated fats by the process of _ ---- 103. Benzene is the parent member of the group of hydrocar- bons called 104. An atom or group of atoms that imparts new and char- Additional problems acteristic properties to an organic molecule is called a _ _ _ group. 89. The first "organic" compound to be synthesized in the laboratory, rather than being isolated from nature, was ____, which was prepared from _ 90. An organic compound whose carbon-carbon bonds are all single bonds is said to be _ 91. The general orientation of the four pairs of electrons around the carbon atoms in alkanes is _ 92. Alkanes in which the carbon atoms form a single unbranched chain are said to be alkanes. 93. Structural isomerism occurs when two molecules have the same number of each type of atom but exhibit different arrangements of the between those atoms. 94. The systematic names of all saturated hydrocarbons have the ending added to a root name that indicates the number of carbon atoms in the molecule. 95. For a branched hydrocarbon, the root name for the hy- drocarbon comes from the number of carbon atoms in the continuous chain in the molecule. 96. The positions of substituents along the hydrocarbon _ frame work of a molecule are indicated by the of the carbon atom to which the substituents are attached. 97. Kerosene may be converted to gasoline by _ which means that the larger, heavier kerosene components are broken down by heat into smaller, lighter gasoline fragments. 98. Tetraethyllead, (C2Hs)4Pb, was added to gasoline in the agent. past as an 99. The major use of alkanes has been in as a source of heat and light. reactions, 100. With very reactive agents, such as the halogen elements, alkanes undergo reactions, whereby a new atom replaces one or more hydrogen atoms of the alkane. 101. Alkenes and alkynes are characterized by their ability to undergo rapid, complete hydrocarbons. reactions, by which 105. A alcohol is one in which there is only one hydrocarbon group attached to the carbon atom holding the hydroxyl group. 106. The simplest alcohol, methanol, is prepared industrially by the hydrogenation of _ 107. Ethanol is commonly prepared by the of cer- tain sugars by yeast. 108. Both aldehydes and ketones contain the group, but they differ in where this group occurs along the hydrocarbon chain. 109. Aldehydes and ketones can be prepared by of the corresponding alcohol. 1l0. Organic acids, which contain the typically weak acids. group, are 111. The typically sweet-smelling compounds called _ result from the condensation reaction of an organic acid with an _ 112. In polymerization, the monomer units simply combine over and over again to form the polymer's long chain. 113. Write the general formula for a normal alkane. How does a given alkane differ from the previous or the following member of the series? 114. Draw structural formulas for all isomeric alkanes having the general formula CSH 12 . 115. As the size of an organic molecule increases, the num- ber of structural isomers that are possible increases dramatically. For the general alkane formula C2oH42 , draw structures showing the carbon framework of at least ten isomers. (You do not have to show all the hydrogen atoms.) 116. Give the systematic name of each of the following sub- stituted alkanes. Additional Problems 123. Draw a structure corresponding to each of the following names. a. 2-methylpentanal b. 3-hydroxybutanoic acid c. 2-aminopropanal d. 2,4-hexanedione e. 3-methylbenzaldehyde d. CH3-CH-CH-CH-CH3 I CI I CI I CI 117. Give some examples of molecules containing "fused" benzene rings. 118. Draw a structural formula for each of the following compounds. a. b. c. d. e. 3-chloro-3-hexene 1,2-dibromoethane 1,1 ,2,2-tetrachloroethane 3-bromo-l-hexyne 1,2-dichloro-2,3,3,4-tetramethyloctane 119. Draw the structural formula(s) for, and give the name(s) of, the organic product(s) of each of the following reactions. If a mixture of several, similar products is expected, indicate the type of product expected. a. CH3-CH3 + Clz ~ c. CH 3 -CH z" /C=CH-CH 3 + Brz 641 ~ CH 3 -CH z 120. For the general formula C6 H 140, draw the structures of three isomeric alcohols that illustrate primary, secondary,. and tertiary alcohol structures. 121. The alcohol glycerol (glycerine), which is produced in the human body by the digestion of fats, has the following structure. Give the systematic name of glycerol. 124. Draw a structure corresponding to each of the following names. a. diphenylketone b. 2-methyl-2-propanol c. methylisopropylketone d. 1,2-ethanediol e. methyl propanoate 125. Salicylic acid is an interesting molecule; it is both an acid and an alcohol, having a hydroxyl group attached to the aromatic ring (phenol). For this reason, salicylic acid clm undergo two different esterification reactions, depending on which functional group of salicylic acid reacts. For example, as discussed in this chapter, when treated with acetic acid-a stronger acid-salicylic acid behaves as an alcohol, and the ester produced is acetylsalicylic acid (aspirin). On the other hand, when reacted with methyl alcohol, salicylic acid behaves as an acid, and the ester methyl salicylate (oil of wintergreen) is produced. Methyl salicylate is also an analgesic and is part of the formulation of many liniments for sore muscles. Write an equation for the production of each of these esters of salicylic acid. 126. Alpha amino acids are organic acid molecules that also happen to contain an amino group (-NH z) on the second carbon atom of the acid's chain. Proteins are condensation polymers of such alpha amino acids. The reaction by which the long chain of the protein forms is very similar to the reaction by which nylon forms, resulting in the formation of the linkage -N-C=O I H I which is called an "amide" (or "peptide") linkage. Show how the following two arilino acids could react with each other to produce an amide linkage, resulting in the formation of a dimer (a "dipeptide"). HO-C=O 122. The sugar glucose could conceivably be given the name 2,3,4,5,6-pentahydroxyhexanal (though this name is never used, because the actual sugar glucose is only one possible isomer having this name). Draw the structure implied by this name. I CH3-CH-N-H I H How could this dipeptide then go on to react with additional amino acids to form a polypeptide? ." 642 20 Organic Chemistry 127. Write structural formulas for the normal (straight-chain) alkanes with: a. seven carbon atoms b. eleven carbon atoms c. sixteen carbon atoms 128. For each of the following numbers of carbon atoms, give the structure of the straight-chain alkane with that number of carbon atoms, and give its name. a. eight carbon atoms b. six carbon atoms c. four carbon atoms d. five carbon atoms 129. Draw structural formulas for all isomeric alkanes having the general formula C 7H 16 . b. CH3CH=CHCH2CH2CH2CH3 c. CH3CH 2C=CCH3 134. Draw suuctural fOlmulas showing all the isomers of the sU'aight-chain alkyne with eight carbon atoms. "Name each isomer. 135. Name each of the following aromatic or substituted aromatic compounds. a b 130. Give the systematic name for each of the following alkanes. a. 0=:: "'IQ(' Br CH 3 I CH 3-CH-CH-CH 3 I CH3 136. On the basis of the functional groups listed in Table 20.5, identify the family of organic compounds to which each of the following belongs. 131. Draw a structural formula for each of the following compounds. a. 2,2-dimethylhexane b. 2,3-dimethylhexane c. 3,3-dimethylhexane d. 3,4-dimethylhexane e. 2,4-dimethylhexane 132. Write the formula for the missing reactant or product in each of the following chemical equations. a. CH4(g) + CI2(g) b. c. + HCl(g) CH3CH2CH3(g) ~ CH3CH=CH2(g) + CHCI3(l) + CI2(g) ~ CCI 4 (l) + _ d. ~ _ 133. Give the systematic name for each of the following unsaturated hydrocarbons. a. CH3CH=CHCH2CH2CH2CH2CH2CH2CH3 137. Draw a structural formula for each of the following alcohols. Indicate whether the alcohol is primary, secondary, or tertiary. a. 2-propanol I I Additional Problems b. 2-methyl-2-propanol c. 4-isopropyl-2-heptanol d. 2,3-dichloro-I-pentanol 138. Draw a structural formula for each of the following: a. 3-methylpentanal b. 3-methyl-2-pentanone c. methyl phenyl ketone d. 2-hydroxybutanal e. propanal I I 139. How are carboxylic acids synthesized? Give an example of an organic acid and the molecule from which it is synthesized. What type of reaction is this? I I 643 140. Draw a structural formula for each ofthe following: a. 3-methylbutanoic acid b. 2-chlorobenzoic acid c. hexanoic acid d. acetic acid 141. Draw the structure of the monomer and the basic repeating unit for each of the following polymeric substances. a. polyethylene b. polyvinyl chloride c. Teflon d. polypropylene e. polystyrene