Practice Problems for Chapter 7 With Answers

Chapter 7

MULTIPLE CHOICE QUESTIONS

Topic: Nomenclature

1. A correct IUPAC name for the following compound is:

A) 3,3,5-trimethyl-2-hexeneB) 3-isobutyl-3-isopropyl-2-propeneC) 3-isobutyl-4-methyl-2-penteneD) 3-(1-methylethyl)-5-methyl-2-hexeneE) None of the above

Ans: D

Topic: Nomenclature

2. The correct IUPAC name for the following compound is:

A) 2-Bromo-4-methylenehexaneB) 2-(2-Bromopropyl)-1-buteneC) 4-Bromo-2-ethyl-1-penteneD) 2-Bromo-4-ethyl-1-penteneE) 2-Bromo-4-ethyl-4-pentene

Ans: C

Topic: Nomenclature

3. Give the IUPAC name for

A) 3-Methyl-4-hexyneB) 4-Methyl-2-hexyneC) 2-Ethyl-3-pentyneD) 4-Ethyl-2-pentyneE) 3-Methyl-2-hexyne

Ans: B

202

Chapter 7

Topic: Nomenclature


A) 4,5-Dimethyl-3-propyl-2-hexeneB) 4,5-Dimethyl-3-propyl-1-hexeneC) 3-(2,3-Dimethylpropyl)-1-hexeneD) 2,3-Dimethyl-4-isopropyl-5-hexeneE) 2,3-Dimethyl-4-propyl-5-hexene

Ans: B

Topic: Nomenclature

5. Select the structure of 4–ethyl-2,3-dimethyl-2-heptene.A)

B)

C)

D)

E)

Ans: B

203

Chapter 7

Topic: Nomenclature

6. Select the structure for cis-3-methyl-6-vinylcyclohexene.

A) IB) IIC) IIID) IVE) V

Ans: B

Topic: Nomenclature


A) (E)-2-Bromo-3-chloro-5-methyl-2-hexeneB) (E)-2-Bromo-3-chloro-5-methyl-3-hexeneC) (Z)-2-Bromo-3-chloro-5-methyl-3-hexeneD) (Z)-2-Bromo-3-chloro-5-methyl-2-hexeneE) (E)-2-Methyl-5-bromo-4-chloro-4-hexene

Ans: A

204

Chapter 7

Topic: Nomenclature

8. The IUPAC name for diisobutylacetylene isA) 2,7-Dimethyl-4-octeneB) 2,7-Dimethyl-4-octyneC) 3,6-Dimethyl-4-octyneD) 2,5-Diethyl-3-hexyneE) 2,2,5,5-Tetramethyl-3-hexyne

Ans: B

Topic: Carbocation Stability, Rearrangement

9. Which of the following carbocations would NOT be likely to undergo rearrangement?A)

B)

C)

D)

E)

Ans: C

205

Chapter 7

Topic: Carbocation stability

10. Which alcohol would initially produce the most stable carbocation when treated with concentrated H2SO4?

A)

B)

C)

D)

E)

Ans: A


11. Which statement(s) is (are) true of acid-catalyzed alcohol dehydrations?A) Protonation of the alcohol is a fast step.B) Formation of a carbocation from the protonated alcohol is a slow step.C) Rearrangements of less stable carbocations to more stable carbocations are common.D) Loss of a proton by the carbocation is a fast step.E) All of the above

Ans: E


12. Carbocations are frequent intermediates in acidic reactions of alkenes, alcohols, etc. What do carbocations usually do? They may:

A) rearrange to a more stable carbocation.B) lose a proton to form an alkene.C) combine with a nucleophile.D) react with an alkene to form a larger carbocation.E) do all of the above.

Ans: E

206

Chapter 7


13. Neopentyl alcohol, (CH3)3CCH2OH, cannot be dehydrated to an alkene without rearrangement. What is the chief product of dehydration?


Ans: B


14. Rearrangements are likely to occur in which of the following reaction types?A) SN1 reactionsB) SN2 reactionsC) E1 reactionsD) E2 reactionsE) Both SN1 and E1 reactions

Ans: E

207

Chapter 7

Topic: Alkene Synthesis, Reaction Mechanisms

15. Which compound listed below would you expect to be the major product when 2-bromo-2-methylbutane is refluxed with KOH/ethanol?

A)

B)

C)

D)

E)

Ans: D


16. Which product(s) would be produced by acid-catalyzed dehydration of 2-methyl-2-pentanol?

A)

B)

C)

D)

E)

Ans: B

208

Chapter 7


17. Which product (or products) would be formed in appreciable amount(s) when trans-1-bromo-2-methylcyclohexane undergoes dehydrohalogenation upon treatment with sodium ethoxide in ethanol?

A) IB) IIC) IIID) IVE) More than one of these

Ans: B

Topic: Alkene Reactions, Reaction Mechanisms

18. Which would be the major product of the following reaction?


Ans: A

209

Chapter 7


19. What is the major product of the reaction,

A) (CH3)2C=C(CH3)2

B) (CH3)3C–CH=CH2

C) (CH3)2C=CHCH3

D) (CH3)2C=CHCH2CH3

E) None of theseAns: B


20. Which compound would be the major product?

A)

B)

C)

D)

E)

Ans: E

210

Chapter 7

Topic: Alkene Synthesis, Reaction Mechanisms, Carbocation Rearrangements

21. What will be the major product of the following reaction?

A)

B)

C)

D)

E)

Ans: A

211

Chapter 7

Topic: Alkene Synthesis, Reaction Mechanisms, Carbocation Rearrangements

22. Which alkene would you expect to be the major product of the following dehydration?


Ans: C

212

Chapter 7

Topic: Alkyne Synthesis, Catalytic hydrogenation

23. The structure of the product, C, of the following sequence of reactions would be:

A)

B)

C)

D)

E)

Ans: A

Topic: Dissolving Metal Reduction; trans-hydrogenation

24. The structure of the product obtained from 2-butyne and Li/C2H5NH2 is:A)

B)

C)

D)

E)

Ans: A

213

Chapter 7

Topic: Catalytic hydrogenation

25. Which alkene would yield 3-methylpentane when subjected to catalytic hydrogenation?A)

B)

C)

D)

E)

Ans: B

Topic: Alkyne Synthesis

26. Which reaction would yield 2-butyne?A) CH3CC:Na + CH3Br B) CH3CH2Br + HCC:Na C) CH3:Na + HCCCH3 D) More than one of theseE) None of these

Ans: A

Topic: Alkyne Synthesis

27. Which of the following methods could be used to synthesize 4,4-dimethyl-2-hexyne?A)

B)

C)

D) More than one of theseE) None of these

Ans: D

214

Chapter 7

Topic: Alkene Synthesis

28. Your task is to convert 2-bromobutane to 1-butene in highest yield. Which reagents would you use?

A) KOH/H2OB) KOH/CH3OHC) CH3ONa/CH3OHD) CH3CH2ONa/CH3CH2OHE) (CH3)3COK/(CH3)3COH

Ans: E

Topic: Alkene Synthesis, Nomenclature

29. Which of the following reactions would yield 3,3-dimethyl-1-butene in a reasonable percentage yield (i.e., greater than 50%)?

A)

B)

C)

D) All of theseE) Answers B) and C) only

Ans: B

215

Chapter 7


30. Which compound(s) would be produced by the following reaction?

A) IB) IIC) IIID) More than one of the aboveE) All of the above

Ans: E

Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms

31. Dehydrohalogenation of tert-pentyl bromide will produce 2-methyl-1-butene as the chief product when:

A) CH3COONa is employed as the base.B) KOH/C2H5OH is employed as the base.C) CH3CH2ONa/CH3CH2OH is employed as the base.D) (CH3)3COK/(CH3)3COH is employed as the base.E) any base is used, as long as the temperature is sufficiently high.

Ans: D


32. Which is not a satisfactory procedure for the synthesis of 3-methyl-1-butene?A) (CH3)2CHCCH3 + conc. H2SO4 B) (CH3)2CHCCH + Li/liq.NH3

C) (CH3)2CHCH2CH2Br + CH3ONa/CH3OHD) (CH3)2CHCHBrCH3 + (CH3)3COK/(CH3)3COHE) (CH3)2CHCCH + H2/Ni2B (P-2)

Ans: A


216

Chapter 7

33. Which of these is the most satisfactory method for the preparation of cis-2-pentene?A) CH3CHBrCH2CH2CH3 + (CH3)3COK/(CH3)3COHB) CH3CCCH2CH3 + H2,PtC) CH3CCCH2CH3 + H2, Ni2B (P-2)D) CH3CCCH2CH3 + Li/liq. NH3

E) CH3CH2CHBrCH2CH3 + CH3CH2ONa/CH3CH2OHAns: C

Topic: Alkyne Reduction, Nomenclature, Reaction Mechanisms

34. Which of the following reductions of an alkyne is NOT correct?A) 2-Pentyne + 2H2/Pt pentaneB) 2-Pentyne + H2/Ni2B Z-2-PenteneC) 2-Pentyne + Li/NH3(l) Z-2-PenteneD) All of the above are correct.E) None of the above is correct.

Ans: C


35. Which of the following reactions would yield 2-pentyne?A)

B)

C)

D)

E)

Ans: B

Topic: Alkyne Synthesis, Nomenclature, Reaction Mechanisms

217

Chapter 7

36. Which reaction would not be a method for preparing 5-methyl-1-hexyne?A)

B)

C)

D)

E)

Ans: C

Topic: Index of Hydrogen Deficiency

37. Compute the index of hydrogen deficiency for the molecule C10H8.A) 3B) 4C) 5D) 6E) 7

Ans: E

Topic: Index of Hydrogen Deficiency

218

Chapter 7

38. Which compound has an index of hydrogen deficiency equal to three?

A) I, IIIB) IV, VC) VD) IIE) II, V

Ans: E

Topic: Index of Hydrogen Deficiency, Nomenclature

39. What is the index of hydrogen deficiency of bicyclo[2.2.2]octane?A) 1B) 2C) 3D) 4E) 5

Ans: B

Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation

40. Which is a possible structure for a compound with an index of hydrogen deficiency equal to 3 and which absorbs one molar equivalent of hydrogen when treated with hydrogen and a platinum catalyst?


Ans: C


219

Chapter 7

41. Upon catalytic hydrogenation, a compound C6H6 absorbs four moles of hydrogen. Select a structure for C6H6.

A) I, IIB) IIIC) II, IIID) IV, VE) I, IV, V

Ans: D


42. A compound, C6H10, which reacts with 2 mol of hydrogen over a platinum catalyst and which shows an IR absorption band at approximately 3300 cm-1 could be:


Ans: C


220

Chapter 7

43. On hydrogenation, a compound C9H12 absorbs 2 mol of hydrogen. Which of the following is a possible structure for the compound?


Ans: D


44. A compound with the formula C10H14 reacts with excess hydrogen and a catalyst to yield a compound with the formula C10H18. The compound could have:

A) one ring and three double bonds.B) two rings and two double bonds.C) two rings and a triple bond.D) no rings and two double bonds.E) More than one of the above

Ans: E


45.

Given: One can conclude that X has:

A) no rings and no double bonds.B) no rings and one double bond.C) one ring and one double bond.D) two rings and no double bonds.E) one triple bond.

Ans: C


221

Chapter 7

46. What is the structure of a compound with formula C6H10 which has IR absorption at approximately 3300 cm-1 and which can be catalytically reduced with hydrogen to 2-methylpentane?

A)

B)

C)

D)

E)

Ans: D


47. A compound X with the formula C7H10 undergoes catalytic hydrogenation to produce a compound Y with the formula C7H14. What might be true of X?

A) X might have one triple bond and one ring.B) X might have two double bonds and one ring.C) X might have one double bond and two rings.D) X might have one double bond and one triple bond.E) More than one of the above

Ans: E

Topic: Alkene Stability, Heats of Hydrogenation and Combustion

48. Which reaction would you expect to liberate the least heat?A)

B)

C)

D)E)

Ans: C


222

Chapter 7

49. One mol of each of the following alkenes is subjected to complete combustion. Which would you expect to liberate the LEAST heat?

A) 1-PenteneB) 2-PenteneC) 2-Methyl-1-buteneD) 2-Methyl-2-buteneE) 3-Methyl-1-butene

Ans: D


50. Which molecule would have the lowest heat of hydrogenation?


Ans: A

Topic: Alkene Stability, Heats of Hydrogenation and Combustion, Nomenclature

51. One mole of each of the following alkenes is subjected to complete combustion. Which would you expect to liberate the most heat?

A) 1-PenteneB) cis-2-PenteneC) 2-Methyl-1-buteneD) 2-Methyl-2-buteneE) trans-2-Pentene

Ans: A


223

Chapter 7

52. Which reaction would you expect to liberate the most heat?A)

B)

C)

D)E)

Ans: C


53. Heats of hydrogenation data would be useful in comparing the relative stabilities of which of the following substances?

A) I, II, IIIB) III, IVC) I, II, VD) Heats of hydrogenation data would not be a useful way to compare relative stabilities of

any of the substancesE) All of the above substances could effectively be compared using heats of hydrogenation

dataAns: C


54. Which alkene would liberate the most heat per mole when subjected to complete combustion?

A)B)C)

D)

E)Ans: A


224

Chapter 7

55. Which alkene would liberate the most heat per mole when subjected to catalytic hydrogenation?

A)B)C)

D)

E)Ans: A


56. One mole of each of the following alkenes is subjected to complete combustion. Which would liberate the least heat?


Ans: D


57. Which alkene is most stable?


Ans: A


225

Chapter 7

58. Concerning the relative stabilities of alkenes, which is an untrue statement?A) Unless hydrogenation of the alkenes gives the same alkane, heats of hydrogenation

cannot be used to measure their relative stabilities.B) In general, the greater the number of alkyl groups attached to the carbon atoms of the

double bond, the greater the stability of the alkene.C) The greater the quantity of heat liberated on combustion or hydrogenation of an alkene,

the greater its energy content.D) trans-Cycloalkenes are always more stable than the cis-isomers.E) Heats of combustion can be used to measure the relative stabilities of isomeric alkenes,

even though their hydrogenation products are not identical.Ans: D

Topic: Relative Acidity of Alkenes, Alkynes; Acid-Base Chemistry

59. Which of the following correctly lists the compounds in order of decreasing acidity?A) H2O > HCCH > NH3 > CH3CH3

B) HCCH > H2O > NH3 > CH3CH3

C) CH3CH3 > HCCH > NH3 > H2OD) CH3CH3 > HCCH > H2O > NH3

E) H2O > NH3 > HCCH > CH3CH3

Ans: A


60. Select the strongest base.A) OH

B) RCC

C) NH2

D) CH2=CH

E) CH3CH2

Ans: E


61. Which ion is the weakest base?A) CH3CH2:

B) CH2=CH:

C) HCC:

D)

E)

Ans: E


226

Chapter 7

62. In the following hydrocarbon, which hydrogen would have the smallest value for pKa? CH3CH2CH=CHCH2CH2CCH

A)

B)

C)

D)

E)

Ans: E

Topic: Relative Acidity of Alkenes, Alkynes; Bond Lengths

63. Which of the following statements is true when ethane, ethene and acetylene are compared with one another?

A) Acetylene is the weakest acid and has the longest C-H bond length.B) Acetylene is the strongest acid and has the shortest C-H bond length.C) Ethane is the strongest acid and has the longest C-H bond length.D) Ethene is the strongest acid and has the shortest C-H bond length.E) Ethene is the weakest acid and has the longest C-H bond length.

Ans: B

Topic: Alkene Synthesis; Alcohol Dehydration

227

Chapter 7

64. Which one of the following alcohols would dehydrate most rapidly when treated with sulfuric acid?


Ans: B


65. Which mechanistic step in the acid-catalyzed dehydration of 3,3-dimethyl-2-butanol is the rate determining step?

A)

B)

C)

D)

E)

Ans: B


228

Chapter 7

66. Which alcohol would be most easily dehydrated?A)

B)

C)

D)

E)

Ans: A


67. Which alcohol would be most easily dehydrated?


Ans: B

Topic: Alkene Structure; Stereochemistry

229

Chapter 7

68. What is the simplest alkene, i.e., the one with the smallest molecular weight, which can exhibit optical activity?

A) 3-methyl-1-penteneB) 3-methyl-2-penteneC) 4-methyl-1-penteneD) 3-methyl-1-buteneE) 4-methyl-2-hexene

Ans: A


69. Determine the total number of stereoisomers which correspond to this general structure:

A) 4B) 6C) 8D) 10E) 12

Ans: C


70. Which can exist as cis-trans isomers?A) 1-PenteneB) 3-HexeneC) CyclopenteneD) 2-Methyl-2-buteneE) 3-Ethyl-2-pentene

Ans: B


71. For which of the following is cis-trans isomerism impossible?A) 2-HexeneB) 3-Methyl-2-penteneC) 3-HexeneD) 2-Methyl-2-buteneE) 2-Pentene

Ans: D


230

Chapter 7

72. Which of the following compounds can exhibit cis-trans isomerism?A) 1-PenteneB) 2-PenteneC) 2-Methyl-2-penteneD) 3-Methyl-1-penteneE) 1-Hexene

Ans: B


73. Which of the following compounds can exhibit cis-trans isomerism? I. 1-Pentene II. 2-Pentene III. 2-Methyl-2-pentene IV. 1,2-Dibromoethene V. 1,1-Dichloroethene

A) II, III, IVB) I, III, VC) II, IVD) II, IIIE) None of these

Ans: C


74. What is the total number of pentene isomers, including stereoisomers?A) 2B) 3C) 4D) 5E) 6

Ans: E

Topic: Nomenclature; Stereochemistry

231

Chapter 7

75. Cis-trans alkenes are often distinguished from each other by examining the spatial orientation of identical groups relative to the double bond. While this often also corresponds to (Z) and (E) descriptions, sometimes it does not. For which of the following alkenes does cis- not equal (Z) or trans not equal (E)?


Ans: C


76. The most specific term used to designate the relationship of cis-3-hexene to trans-3-hexene is:

A) stereoisomers.B) enantiomers.C) diastereomers.D) constitutional isomers.E) conformational isomers.

Ans: C


77. How many stereoisomers can be predicted for 4–ethyl-2,3-dimethyl-2-heptene?A) 1B) 2C) 3D) 4E) None of the above

Ans: B

Topic: General Information, Bonding

232

Chapter 7

78. How many sigma bonds are there in CH2=CH–CCH?A) 6B) 7C) 8D) 9E) 10

Ans: B

Topic: General Information, Bonding

79. What characteristic(s) of alkynes would make it difficult to prepare cyclohexyne?A) The requirement for linearity at the triple bond centerB) The large electron density between carbons of a triple bondC) The short carbon-carbon triple bond lengthD) The need that the carbon-carbon triple bond be internal in the chainE) All of these

Ans: A

Topic: General Information, Nomenclature

80. The ambiguous name "methylcyclohexene" does not differentiate among this number of compounds (ignoring stereoisomers):

A) 2B) 3C) 4D) 5E) 6

Ans: B


81. Zaitsev's rule states that:A) In electrophilic addition of an unsymmetrical reagent to an unsymmetrical alkene, the

more positive portion of the reagent will become attached to the carbon of the double bond bearing the greater number of hydrogen atoms.

B) An equatorial substituent in cyclohexane results in a more stable conformation than if that substituent were axial.

C) E2 reactions occur only if the -hydrogen and leaving group can assume an anti-periplanar arrangement.

D) When a reaction forms an alkene, and several possibilities exist, the more (or most) stable isomer is the one which predominates.

E) The order of reactivity of alcohols in dehydration reactions is 3º > 2º > 1º.Ans: D


233

Chapter 7

82. Regarding the use of potassium tert-butoxide as a base in E2 reactions, it is incorrect to state that:

A) this base is more effective than ethoxide ion, because it (KO-t-Bu) is the more basic of the two.

B) it tends to give the anti-Zaitsev, i.e., Hofmann, product.C) it is more reactive in dimethyl sulfoxide than it is in tert-butyl alcohol.D) it favors E2 reactions over competing SN2 reactions.E) it will form, predominantly, the more stable alkene.

Ans: E

Topic: General Information

83. When an elimination reaction gives the most stable alkene as the major product, we say that the elimination follows ________________'s rule.Ans: Zaitsev


84. When an elimination reaction gives the less substituted alkene as the major product, we say that the elimination follows ________________'s rule.Ans: Hofmann


85. In a dehydration reaction, the leaving group is _______________.Ans: a molecule of water


86. In hydrogenation reactions, both hydrogen atoms add to the pi system from the same face of the molecule. This is an example of a(n) _________ addition.Ans: syn


87. Syn hydrogenation of an alkyne will produce a _________ alkene.Ans: Cis / Z


88. Dehydration of alcohols requires a __________________ catalyst.Ans: strong acid


234

Chapter 7

89. Carbocations have three options available for further reaction. These options include reaction with a nucleophile, loss of a beta proton to give an alkene, and ________________.Ans: rearrangement


90. Alkynes can be produced from either __________________ or _________________ dihalides.Ans: vicinal/geminal


91. Conversion of alkynes to E-alkenes (trans-alkenes) can be accomplished via a __________________ reaction.Ans: dissolving metal reduction

Topic: Nomenclature, Bonding

92. The number of (s-sp2) bonds in a molecule of 2,3-dimethyl-2,4-heptadiene is _____.Ans: two

Topic: Alkene Hydrogenation

93. How will you prepare cis-1,2-dimethylcyclohexane from 1,2-dimethylcyclohexene?Ans: Catalytic hydrogenation with H2, Ni (or Pt/Pd)

Topic: Alkyne Reduction

94. How will you prepare trans-2-heptene from 2-heptyne?Ans: Dissolving metal reduction with metallic Na in NH3(l).

SHORT EXPLANATION / STRUCTURE DRAWING QUESTIONS

235

Chapter 7

Topic: Nomenclature, Stereochemistry

95. Draw the structures of all stereoisomers of 2-chloro-4-methyl-3-hexene, clearly showing all stereochemical details, using appropriate 3-D representations (dash-wedge, etc.) as relevant.Ans:

Topic: Alkene Nomenclature, Relative Stability

96. The ambiguous name dimethylcyclopentene does not clearly distinguish between several structures. a) Draw the structures of all constitutional isomers corresponding to this name. b) Indicate which of these is likely to be the most stable, i.e, have the smallest heat of combustion, justifying your rationale briefly. c) Which of these structures represents an achiral molecule?Ans: a)

b) Structure I is likely to be the most stable, because it is a tetra-substituted alkene: II, IV and V are tri-substituted; III and VI are di-substituted.c) Structure I is achiral

Topic: Alkyne Synthesis, Acid-Base reactions

236

Chapter 7

97. Complete the following reaction sequence, providing a brief rationale for your answer.

Ans:

Reaction with PCl5 would afford a geminal dihalide I, which would undergo E2 elimination when heated, losing 2 moles of HCl to afford the alkyne III. However, since III is a terminal alkyne, it has a hydrogen atom that is labile in presence of NaNH2; hence, an extra mole equivalent of the base is required to ensure complete reaction and convert all of the initially formed III into the sodium alkynide intermediate, II; this, upon acidification, affords the final alkyne product III.

Topic: Alkyne Synthesis, Alkyne Hydrogenation

98. Complete the following reaction, giving structural details of all intermediates as well as the final product.

Ans:


237

Chapter 7

99. What “new”, more stable, carbocation(s) may be formed when the following carbocation undergoes spontaneous rearrangement?

Ans:

Topic: Nomenclature, Multistep Synthesis

100. Propose a two-step synthetic strategy for the synthesis of 2-methylhexane from 5-methyl-2-hexanol.Ans:

Step 1:Acid-catalyzed dehydration of 5-methyl-2-hexanol to yield an isomeric mixture of 5-methyl-1-hexene and 5-methyl-2-hexene Step 2:Catalytic hydrogenation of the double bond with H2, Ni to yield the desired 2-methylhexane

Topic: Nomenclature, Multistep Synthesis

101. Propose a reasonable synthetic strategy for the synthesis of trans-6-methyl-3-heptene from 4-methyl-1-pentyne.Ans:

Step 1:Add NaNH2/NH3(l) to selectively deprotonate the alkyne hydrogen.Step 2:Add ethyl iodide to give 6-methyl-3-pentyne by an SN2 process.Step 3:Add Na(s)/NH3(l) to give the desired trans-alkene by dissolving metal reduction.

Topic: Carbocation Rearrangement, Alkene Synthesis, Dehydration Mechanism

238

Chapter 7

102. Provide a mechanistic explanation for the formation of the observed products in the following reaction.

Ans:

Topic: Nomenclature, Index of Hydrogen Deficiency, IR Spectroscopy, Catalytic Hydrogenation

239

Chapter 7

103. The IR spectrum of an unknown substance Q, C9H16, is found to have distinct peaks at 3310 cm-1 and 2140 cm-1. Treatment of Q with excess H2 in presence of Raney Ni affords nearly quantitative yields of 2,3-dimethylheptane. Propose a reasonable structure for Q, based on the above information, briefly explaining your rationale. Also give its IUPAC name.Ans:

The Index of Hydrogen deficiency of Q is 2 (compared with C9H20). The IR data suggests that Q is a terminal alkyne; thus, there must be no rings in its structure. The catalytic hydrogenation data provides further details of the carbon skeleton. Due to the specific substitution pattern in this carbon skeleton, there is only one possible position for a terminal triple bond. Thus, the structure given above is consistent with all of the given information.IUPAC Name: 5,6-dimethyl-1-heptyne

240

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