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Organic Chemistry, 8e (Wade) Chapter 3 Structure and Stereochemistry of Alkanes 1) Which of the statements below accurately describe(s) alkanes? A) Alkanes are hydrocarbons which contain only single bonds. B) Alkanes belong to the class of unsaturated hydrocarbons. C) Alkanes are the simplest and le...

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Organic Chemistry, 8e (Wade) Chapter 3 Structure and Stereochemistry of Alkanes 1) Which of the statements below accurately describe(s) alkanes? A) Alkanes are hydrocarbons which contain only single bonds. B) Alkanes belong to the class of unsaturated hydrocarbons. C) Alkanes are the simplest and least reactive class of organic compounds. D) both A and B E) both A and C Answer: E Diff: 1 Section: 3.1 2) Which of the following types of hydrocarbons is(are) saturated? A) alkanes B) alkenes C) alkynes D) aromatics E) All of the above are saturated. Answer: A Diff: 1 Section: 3.1 3) If a hydrocarbon has no double or triple bonds, it is said to be ________. Answer: saturated Diff: 1 Section: 3.1 4) Straight-chain alkanes are also called ________. Answer: n-alkanes Diff: 2 Section: 3.1

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5) The structure below is a potent analgesic agent (pain reliever) (J. Med. Chem., 2009, 5685). How many secondary carbons are in this structure?

A) 2 B) 4 C) 6 D) 12 Answer: A Diff: 2 Section: 3.1 6) If an acyclic alkane hydrocarbon contains n carbon atoms, how many hydrogen atoms must it also contain? A) n B) 2n C) n + 2 D) 2n + 2 E) n - 2 Answer: D Diff: 2 Section: 3.2 7) A series of compounds, like the n-alkanes, that differ only by the number of -CH2- groups, is called a(n) ________ series. Answer: homologous Diff: 2 Section: 3.2 8) A bicyclic alkane contains 12 carbon atoms. How many hydrogen atoms does it contain? A) 20 B) 22 C) 24 D) 26 E) 28 Answer: B Diff: 2 Section: 3.2

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9) How many methylene groups are present in 2,4-dimethylhexane? A) 0 B) 1 C) 2 D) 6 E) 8 Answer: C Diff: 2 Section: 3.2 10) Triacontane is an unbranched alkane that contains 30 carbon atoms in each molecule. How many hydrogen atoms are present in each molecule of triacontane? A) 30 B) 32 C) 58 D) 60 E) 62 Answer: E Diff: 3 Section: 3.2 11) How many secondary (2°) carbons are found in 5-ethyl-3,3,4-trimethylheptane? A) 1 B) 4 C) 2 D) 3 E) 6 Answer: D Diff: 1 Section: 3.3 12) Provide an acceptable name for (CH3CH2CH2)3CH. Answer: 4-propylheptane Diff: 1 Section: 3.3 13) Provide the name of the compound below.

Answer: 3-fluoro-2,2-dimethylhexane Diff: 1 Section: 3.3

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14) Provide the name of the compound below.

Answer: 2,3,6,7-tetramethylnonane Diff: 1 Section: 3.3 15) Provide an acceptable name for the alkane shown below. CH3CH2CH2CH2CH2CH3 Answer: hexane or n-hexane Diff: 1 Section: 3.3 16) Provide an acceptable name for the alkane shown below.

Answer: 2,5-dimethylheptane Diff: 1 Section: 3.3 17) Draw an acceptable structure for 4-tert-butyloctane. Answer:

Diff: 1 Section: 3.3 18) Draw an acceptable structure for 3-ethyl-3-methylhexane. Answer:

Diff: 1 Section: 3.3

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19) Draw an acceptable structure for 4-isopropyl-2-methylheptane. Answer:

Diff: 1 Section: 3.3 20) Name the haloalkane shown.

Answer: 3,4-dibromoheptane Diff: 1 Section: 3.3 21) Provide an acceptable name for the following compound.

Answer: 4,4-dichloro-6-isopropyl-3-methylnonane Diff: 2 Section: 3.3 22) Provide an acceptable name for the [(CH3)3C]2CHCH3. Answer: 2,2,3,4,4-pentamethylpentane Diff: 2 Section: 3.3 23) Provide the IUPAC name of (CH3CH2)3CH. Answer: 3-ethylpentane Diff: 2 Section: 3.3

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24) Provide the IUPAC name of (CH3)2CHCH2CH2C(CH3)3. Answer: 2,2,5-trimethylhexane Diff: 2 Section: 3.3 25) Predict the molecular formula of 4-ethyl-5,5-dimethyldodecane. Answer: C16H34 Diff: 2 Section: 3.3 26) Provide an acceptable name for the alkane shown below.

Answer: 5-sec-butyl-2,2-dimethylnonane or 2,2-dimethyl-5-(1-methylpropyl)nonane Diff: 2 Section: 3.3 27) Provide an acceptable name for the alkane shown below.

Answer: 4-isopropyldecane or 4-(1-methylethyl)decane Diff: 2 Section: 3.3 28) Provide an acceptable name for the alkane shown below.

Answer: 3-ethyl-4,4-dimethylheptane Diff: 2 Section: 3.3

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29) Draw an acceptable structure for 6-ethyl-2,6,7-trimethyl-5-propylnonane. Answer:

Diff: 2 Section: 3.3 30) Provide an acceptable name for the alkane shown below.

Answer: 2,2,3,6-tetramethylheptane Diff: 2 Section: 3.3 31) Provide an acceptable name for the alkane shown below.

Answer: 6-ethyl-2-methyl-5-propyldecane Diff: 2 Section: 3.3 32) Provide an acceptable name for the alkane shown below.

Answer: 5-ethyl-2,2-dimethylheptane Diff: 2 Section: 3.3

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33) Identify the correct IUPAC name for the following structures.

A) 4-(2-iodo-1-methylethyl)-3-methylheptane B) 3-s-butyl-1-iodo-2-methylhexane C) 1-iodo-2,4-dimethyl-3-propylhexane D) 2,4-dimethyl-1-iodo-3-propylhexane Answer: A Diff: 2 Section: 3.3 34) Name the haloalkane shown. CH3CH2C(CH3)2CH2CH2I Answer: 1-iodo-3,3-dimethylpentane Diff: 2 Section: 3.3 35) Name the alkane shown. [(CH3)2CH]2CHCH3 Answer: 2,3,4-trimethylpentane Diff: 2 Section: 3.3 36) Name the alkane shown.

Answer: 5-ethyl-2,2-dimethyloctane Diff: 2 Section: 3.3

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37) How many methyl groups are present in 2,4-dimetylhexane? A) 0 B) 2 C) 4 D) 6 E) 8 Answer: C Diff: 2 Section: 3.3 38) Identify the correct IUPAC name for the following structure.

A) 6-bromo-1-cyclopentyl-3,6-dimethylhexane B) 1-bromo-5-cyclopentyl-1,4-dimethylpentane C) 2-bromo-6-cyclopentyl-5-methylhexane D) 5-bromo-1-cyclopentyl-2-methylhexane E) none of the above Answer: D Diff: 3 Section: 3.3 39) Identify the correct IUPAC name for each compound shown below.

A) 2-bromo-3-sec-butyl-4-ethylhexane B) 2-bromo-4-ethyl-3-sec-butylhexane C) 3-(1-bromoethyl)-2,4-diethylhexane D) 4-(1-bromoethyl)-3-ethyl-5-methylheptane E) 4-(1-bromoethyl)-5-ethyl-3-methylheptane Answer: D Diff: 3 Section: 3.3

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40) Provide the name of the compound shown.

Answer: 2,2,7-trichloro-4-ethyl-6-isobutyl-7,10-dimethyldodecane Diff: 3 Section: 3.3 41) Give structures for the three isomers with molecular formula C5H12 and provide the common name of each. Answer:

Diff: 3 Section: 3.3 42) Provide an acceptable name for the alkane shown below.

Answer: 3-ethyl-7-methyl-5-propylnonane Diff: 3 Section: 3.3 43) Draw an acceptable structure for 4-ethyl-6-(1,2-dimethylpropyl)decane. Answer:

Diff: 3 Section: 3.3

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44) Draw an acceptable structure for 1-ethyl-2-(2,2-dimethylpentyl)cyclopentane. Answer:

Diff: 3 Section: 3.3 45) When one compares the densities of n-hexane and water, one finds: A) that n-hexane is less dense than water. B) that n-hexane is more dense than water. C) that these two compounds have the same density. D) that the relative densities of two immiscible compounds cannot be measured. Answer: A Diff: 1 Section: 3.4 46) A branched alkane has ________ boiling point relative to the isomeric linear alkane. There are ________ London force interactions in the branched alkane A) a higher; stronger B) a higher; weaker C) a lower, stronger D) a lower; weaker E) the same; similar Answer: D Diff: 1 Section: 3.4 47) Consider the three isomeric alkanes n-hexane, 2,3-dimethylbutane, and 2-methylpentane. Which of the following correctly lists these compounds in order of increasing boiling point? A) 2,3-dimethylbutane < 2-methylpentane < n-hexane B) 2-methylpentane < n-hexane < 2,3-dimethylbutane C) 2-methylpentane < 2,3-dimethylbutane < n-hexane D) n-hexane < 2-methylpentane < 2,3-dimethylbutane E) n-hexane < 2,3-dimethylbutane < 2-methylpentane Answer: A Diff: 2 Section: 3.4 48) A branched alkane generally melts at a ________ temperature than the n-alkane containing the same number of carbons. Answer: lower Diff: 2 Section: 3.4

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49) ________ is the n-alkane of greatest molecular weight which is a gas at room temperature and pressure. Answer: Butane Diff: 2 Section: 3.4 50) Place the following alkanes in order of increasing boiling point: CH3(CH2)6CH3, CH3(CH2)5CH3, (CH3)3CCH2CH2CH3 Answer: (CH3)3CCH2CH2CH3 < CH3(CH2)5CH3 < CH3(CH2)6CH3 Diff: 2 Section: 3.4 51) Why are alkanes described as hydrophobic? Answer: Alkanes are nonpolar and as such they do not dissolve to any appreciable extent in water. Diff: 2 Section: 3.4 52) Which intermolecular force is primarily responsible for the interactions among alkane molecules? Answer: van der Waals or London forces Diff: 2 Section: 3.4 53) What is the major constituent of natural gas? A) octane B) butane C) propane D) ethane E) methane Answer: E Diff: 1 Section: 3.5 54) Within the context of commercial uses of alkanes, explain what "knocking" is. Answer: "Knocking" is the potentially damaging, premature explosive combustion of certain gasoline mixtures in a car's engine. Diff: 1 Section: 3.5

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55) Natural gas is primarily composed of A) oxygen. B) carbon dioxide. C) methane. D) octane. E) ethanol. Answer: C Diff: 1 Section: 3.5 56) Which alkanes have largely replaced Freons as propellants in aerosol cans? A) methane and ethane B) propane and butane C) pentane and hexane D) nonane and decane E) none of the above Answer: B Diff: 2 Section: 3.5 57) How many carbons do the primary alkane constituents of gasoline contain? A) C1 C2 B) C3 C4 C) C5 C8 D) C8 C12 E) C12 C16 Answer: C Diff: 2 Section: 3.5 58) ________ is the reaction process through which long-chain alkanes are converted into a mixture of short-chain alkanes and alkenes. Answer: Catalytic cracking Diff: 2 Section: 3.5 59) List three commercial products which are composed primarily of alkanes. Answer: natural gas, gasoline, kerosene, heating oil, lubricating oil, liquefied petroleum gas, jet fuel, diesel oil, petroleum jelly Diff: 2 Section: 3.5 60) Name the two major steps in the refining of crude oil into usable hydrocarbon products. Answer: 1. fractional distillation 2. cracking (catalytic cracking and/or hydrocracking) Diff: 2 Section: 3.5 13 Copyright © 2013 Pearson Education, Inc.

61) In the complete combustion of heptane, how many moles of water are produced? Answer: 8 Diff: 2 Section: 3.6 62) By using the appropriate molecular formulas, write a balanced equation which describes the complete combustion of cyclohexane. Answer: C6H12 + 9 O2 → 6 CO2 + 6 H2O Diff: 2 Section: 3.6 63) When a mole of decane undergoes complete combustion, how many moles of water are formed? A) 1 B) 10 C) 11 D) 15.5 E) 22 Answer: C Diff: 2 Section: 3.6 64) By using the appropriate molecular formulas, write a balanced equation which describes the complete combustion of nonane. Answer: CH3(CH2)7CH3 + 14 O2 → 9 CO2 + 10 H2O Diff: 3 Section: 3.6 65) The energy barrier for carbon-carbon bond rotation in propane is mainly due to ________. A) angle strain B) bond strain C) muscle strain D) steric strain E) torsion strain Answer: E Diff: 1 Section: 3.7

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66) The structures below are:

A) not isomers. B) conformational isomers. C) cis-trans isomers. D) structural isomers. E) both B and D Answer: D Diff: 2 Section: 3.7 67) Which of the following best describes the molecules of a sample of ethane gas at room temperature? A) Almost all of the molecules are frozen or locked in the eclipsed conformation. B) Almost all of the molecules are frozen or locked in the staggered conformation. C) The molecules are rapidly interconverting between the eclipsed and staggered conformations, but at any one time slightly more of them are present in the eclipsed conformation. D) The molecules are rapidly interconverting between the eclipsed and staggered conformations, but at any one time slightly more of them are present in the staggered conformation. Answer: D Diff: 2 Section: 3.7 68) Draw a Newman projection of the most stable conformation of 2-methylpropane. Answer:

Diff: 2 Section: 3.7 69) Define the term conformation. Answer: Conformations are different arrangements of the same molecule formed by rotations about single bonds. Diff: 2 Section: 3.7

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70) Use a sawhorse structure to depict the eclipsed conformer of ethane. Answer:

Diff: 2 Section: 3.7 71) Draw the Newman projection of the highest energy conformation that results from rotation about the C2-C3 bond of 2,2-dimethylbutane. Answer:

Diff: 1 Section: 3.8 72) Which of the following statements concerning the conformers of butane is true? A) Unlike ethane, all butane conformers are classified as eclipsed. B) The lowest energy conformer of butane is the gauche conformer. C) There is more torsional strain in the anti conformer than in the totally eclipsed conformer. D) The eclipsed and totally eclipsed conformers have the same amount of nonbonded strain. E) The gauche and anti conformers differ primarily in the amount of nonbonded strain present. Answer: E Diff: 2 Section: 3.8 73) Draw the Newman projection of the lowest energy conformation that results from rotation about the C2-C3 bond of 2-methylbutane. Answer:

Diff: 2 Section: 3.8

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74) Draw the Newman projection of the lowest energy conformation that results from rotation about the C2-C3 bond of 2,2-dimethylbutane. Answer:

Diff: 2 Section: 3.8 75) Draw the Newman projection of the highest energy conformation that results from rotation about the C2-C3 bond of 2-methylbutane. Answer:

Diff: 2 Section: 3.8 76) Consider rotation about the C3-C4 bond of hexane, and draw the Newman projection for the most stable conformation. Answer:

Diff: 2 Section: 3.8 77) Arrange the following conformers of butane in order of energy, lowest to highest: eclipsed, totally eclipsed, gauche, and anti. Answer: anti < gauche < eclipsed < totally eclipsed Diff: 2 Section: 3.8

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78) Among the butane conformers, which occur at energy minima on a graph of potential energy versus dihedral angle? A) gauche only B) eclipsed and totally eclipsed C) gauche and anti D) eclipsed only E) anti only Answer: C Diff: 3 Section: 3.8 79) For the compound represented by the Newman projection below, what is the dihedral angle between the methyl groups in the conformer that has the smallest molecular dipole moment?

A) 0° B) 30° C) 60° D) 120° E) 180° Answer: C Diff: 3 Section: 3.8 80) Without any change in conformation, translate the Newman projection shown below to a perspective structure.

Answer:

Diff: 3 Section: 3.8

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81) View a butane molecule along the C2 C3 bond and provide a Newman projection of the lowest energy conformer. Answer:

Diff: 3 Section: 3.8 82) Provide a representation of the gauche conformer of butane. Answer:

Diff: 3 Section: 3.8 83) From the perspective of viewing down the C2 C3 bond, draw the Newman projection of the most stable conformation of 2,3-dimethylbutane. Answer:

Diff: 3 Section: 3.8 84) From the perspective of viewing down the C2-C3 bond, draw the Newman projection of the least stable conformation of 2,3-dimethylbutane. Answer:

Diff: 3 Section: 3.8

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85) In a Newman projection, siting down the C3-C4 bond, draw the structure below in its most stable conformation.

Answer:

Diff: 3 Section: 3.9 86) If a monocyclic alkane hydrocarbon contains n carbon atoms, how many hydrogen atoms must it also contain? A) n B) 2n C) n + 2 D) 2n + 2 E) n - 2 Answer: B Diff: 1 Section: 3.10 87) Give the IUPAC name for the cycloalkane shown below.

Answer: trans-1-ethyl-2-methylcyclopentane Diff: 1 Section: 3.10 88) Give the IUPAC name for the cycloalkane shown below.

Answer: cis-1-isopropyl-3-methylcycloheptane Diff: 1 Section: 3.10

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89) What element of ring strain exists in cyclooctane but not in cyclopropane? Answer: transannular strain Diff: 1 Section: 3.10 90) Provide an acceptable name for the following compound.

Answer: isobutylcyclopentane or (2-methylpropyl)cyclopentane Diff: 2 Section: 3.10 91) Provide the name of the compound below.

Answer: sec-butylcycloheptane Diff: 2 Section: 3.10 92) Identify the correct IUPAC name for the structure shown below.

A) 1-tert-butyl-2-chloro-5-bromocycloheptane B) 5-bromo-1-tert-butyl-2-chlorocycloheptane C) 1-bromo-4-chloro-5-tertbutylcycloheptane D) 1-bromo-4-tert-butyl-5-chlorocycloheptane E) 1-tert-butyl-4-bromo-7-chlorocycloheptane Answer: B Diff: 3 Section: 3.10

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93) Given the following heats of combustion per CH2 group within the structure, which cyclic alkane has essentially no angle strain? (Ref: long-chain Alkane = 659 kJ/mol) A) cyclobutane = 686 kJ/mol B) cyclopentane = 664 kJ/mol C) cyclohexane = 659 kJ/mol D) cycloheptane = 662 kJ/mol E) cyclooctane = 663 kJ/mol Answer: C Diff: 1 Section: 3.12 94) Which of the following cycloalkanes exhibits the greatest molar heat of combustion? A) cyclooctane B) cycloheptane C) cyclohexane D) cyclobutane E) cyclopropane Answer: A Diff: 2 Section: 3.12 95) Which of the following correctly ranks the cycloalkanes in order of increasing ring strain per methylene? A) cyclopropane < cyclobutane < cyclohexane < cyclopentane B) cyclohexane < cyclopentane < cyclobutane < cyclopropane C) cyclohexane < cyclobutane < cyclopentane < cyclopropane D) cyclopentane < cyclopropane < cyclobutane < cyclohexane E) cyclopropane < cyclopentane < cyclobutane < cyclohexane Answer: B Diff: 2 Section: 3.12 96) Which of the following cycloalkanes has the smallest heat of combustion per CH2 group? A) cyclopropane B) cyclobutane C) cyclopentane D) cyclohexane E) cycloheptane Answer: D Diff: 2 Section: 3.12

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97) Which of the following statements regarding cyclobutane is correct? A) The lowest energy conformation of cyclobutane is a planar one in which all of the bond angles is 90°. B) The lowest energy conformation of cyclobutane is known as the chair conformation. C) The lowest energy conformation is one in which the bond angles are slightly less than 90° even though this increases angle strain. D) The lowest energy conformation is one in which the bond angles are greater than 90° so that angle strain is significantly reduced. E) None of the above statements is correct. Answer: C Diff: 3 Section: 3.12 98) Which has the greatest molar heat of combustion? A) trans-1,2-dimethylcyclopentane B) cis-1,2-dimethylcyclopentane C) trans-1,3-dimethylcyclopentane D) methylcyclohexane E) cycloheptane Answer: B Diff: 3 Section: 3.12 99) Describe the sources of angle strain and torsional strain present in cyclopropane. Answer: The angle strain arises from the compression of the ideal tetrahedral bond angle of 109.5° to 60°. The large torsional strain occurs since all C H bonds on adjacent carbons are eclipsed. Diff: 3 Section: 3.12 100) The twisted boat conformation of cyclohexane is actually a slightly lower energy conformation than the boat conformation. Which of the following accurately describes one factor involved in this structural behavior ? A) lower angle strain in the boat B) higher torsional strain in the twisted boat C) fewer unfavorable steric factors in the twisted boat D) increased rotational freedom in the boat E) lower bond strain in the boat Answer: C Diff: 1 Section: 3.13

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