CHEM243- Chapter 3 Structure and Stereochemistry of Alkanes

FALSE

(true/false) The structures below are the same.

B) 22

A bicyclic alkane contains 12 carbon atoms. How many hydrogen atoms does it contain? A) 20 B) 22 C) 24 D) 26 E) 28

D) a lower; weaker

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

C6H12 + 9 O2 → 6 CO2 + 6 H2O

By using the appropriate molecular formulas, write a balanced equation which describes the complete combustion of cyclohexane.

CH3(CH2)7CH3 + 14 O2 → 9 CO2 + 10 H2O

By using the appropriate molecular formulas, write a balanced equation which describes the complete combustion of nonane.

The lowest-energy conformation for any straight-chain alkane is the one with all the internal carbon-carbon bonds in their anti conformations. These anti conformations give the chain a zigzag shape.

Explain why the lowest energy conformation of decane is an extended, or zig-zag conformation.

cis-1-isopropyl-3-methylcycloheptane

Give the IUPAC name for the cycloalkane shown below.

trans-1-ethyl-2-methylcyclopentane

Give the IUPAC name for the cycloalkane shown below.

C) cyclohexane = 659 kJ/mol

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

C) C5—C8

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

A) 2

The structure below is a potent analgesic agent (pain reliever) (J. Med. Chem., 2009, 5685). How many secondary carbons are in this structure? [insert image] A) 2 B) 4 C) 6 D) 12

D) structural isomers

The structures below are ________. A) not isomers B) conformational isomers C) cis-trans isomers D) structural isomers E) both B and D

3,4-dibromoheptane

Name the haloalkane shown.

1-iodo-3,3-dimethylpentane

Name the haloalkane shown. CH3CH2C(CH3)2CH2CH2I

homologous

A series of compounds, like the n-alkanes, that differ only by the number of groups, is called a(n) ________ series.

2-methyl-4-propylheptane is the correct name. The name was incorrect because although heptane is the longest chain in both names, the substituent isobutyl is branched, while methyl and propyl are not.

A student named the following molecule "4-isobutylheptane." Why is this incorrect? What is the correct name?

C) gauche and anti

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

A) I<III<II<IV

Arrange the following Newman projections of butane in order of energy. A) I<III<II<IV B) IV<II<III<I C) III<I<IV<II D) II<IV<I<III

anti < gauche < eclipsed < totally eclipsed

Arrange the following conformers of butane in order of energy, lowest to highest: eclipsed, totally eclipsed, gauche, and anti.

F) Both A and C are correct.

Assuming a chair conformation, which of the following configurations will always have both methyl groups in relative axial/equatorial positions? A) trans-1,3-dimethylcyclohexane B) cis-1,3-dimethylcyclohexane C) cis-1,2-dimethylcyclohexane D) trans-1,2-dimethylcyclohexane E) Both B and D are correct. F) Both A and C are correct.

C) The K where X = CH(CH3)2 is greater.

Consider the equilibrium shown below. When one looks at the equilibrium where X = CH3 and the one where X = CH(CH3)2, how do the values of the equilibrium constants (Ks) compare? A) The Ks are equal. B) The K where X = CH3 is greater. C) The K where X = CH(CH3)2 is greater. D) The Ks differ only slightly and are both less than 1.

A) 2,3-dimethylbutane < 2-methylpentane < n-hexane

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

Conformations are different arrangements of the same molecule formed by rotations about single bonds.

Define the term conformation.

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.

Describe the sources of angle strain and torsional strain present in cyclopropane.

C) 4

How many methyl groups are present in 2,4-dimethylhexane? A) 0 B) 2 C) 4 D) 6 E) 8

C) 2

How many methylene groups are present in 2,4-dimethylhexane? A) 0 B) 1 C) 2 D) 6 E) 8

D) 3

How many secondary (2°) carbons are found in 5-ethyl-3,3,4-trimethylheptane? A) 1 B) 4 C) 2 D) 3 E) 6

D) 4-(1-bromoethyl)-3-ethyl-5-methylheptane

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

D) 5-bromo-1-cyclopentyl-2-methylhexane

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

A) 4-(2-iodo-1-methylethyl)-3-methylheptane

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

B) 5-bromo-1-tert-butyl-2-chlorocycloheptane

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

saturated

If a hydrocarbon has no double or triple bonds, it is said to be ________.

B) 2n

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

D) 2n + 2

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

trans - 1-bromo-3-(tert-butyl)cyclohexane

Name the following compound and use the appropriate cis/trans designation.

D) on C-1 and C-4

In the boat conformation of cyclohexane, the "flagpole" hydrogens are located ________. A) on the same carbon B) on adjacent carbons C) on C-1 and C-3 D) on C-1 and C-4 E) none of the above

8

In the complete combustion of heptane, how many moles of water are produced?

E) 6

In the lowest energy chair conformation of cis-1,3-dimethylcyclohexane, how many axial positions are occupied by hydrogen atoms? A) 2 B) 3 C) 4 D) 5 E) 6

A) 0

In the lowest energy conformation of the compound below, how many alkyl substituents are axial? A) 0 B) 1 C) 2 D) 3 E) 6

C) 2

In the lowest energy conformation of the compound below, how many alkyl substituents are equatorial? A) 0 B) 1 C) 2 D) 3 E) 6

Cyclohexane is more symmetric molecule and doesn't have as many degrees of freedom or conformational flexibility as hexane. This allows it to pack in a more regular lattice and has stronger IMFs between the molecules and therefore a higher boiling point.

Linear alkanes generally have higher phase transitions than their branched isomers. However, the melting point of cyclohexane is 6° C while the melting point of hexane is -95° C. Briefly suggest a reason why this is.

natural gas, gasoline, kerosene, heating oil, lubricating oil, liquefied petroleum gas, jet fuel, diesel oil, petroleum jelly

List three commercial products which are composed primarily of alkanes.

5-ethyl-2,2-dimethyloctane

Name the alkane shown.

2,3,4-trimethylpentane

Name the alkane shown. [(CH3)2CH]2CHCH3

(CH3)3CCH2CH2CH3 < CH3(CH2)5CH3 < CH3(CH2)6CH3

Place the following alkanes in order of increasing boiling point: CH3(CH2)6CH3, CH3(CH2)5CH3, (CH3)3CCH2CH2CH3

C16H34

Predict the molecular formula of 4-ethyl-5,5-dimethyldodecane

4-propylheptane

Provide an acceptable name for (CH3CH2CH2)3CH.

2,2,3,4,4-pentamethylpentane

Provide an acceptable name for [(CH3)3C]2CHCH3

5-sec-butyl-2,2-dimethylnonane or 2,2-dimethyl-5-(1-methylpropyl)nonane

Provide an acceptable name for the alkane shown below

2,2,3,6-tetramethylheptane

Provide an acceptable name for the alkane shown below.

2,5-dimethylheptane

Provide an acceptable name for the alkane shown below.

2-fluoro-7-methyl-5-propyldecane

Provide an acceptable name for the alkane shown below.

3-ethyl-4,4-dimethylheptane

Provide an acceptable name for the alkane shown below.

3-ethyl-7-methyl-5-propylnonane

Provide an acceptable name for the alkane shown below.

4-isopropyldecane or 4-(1-methylethyl)decane

Provide an acceptable name for the alkane shown below.

6-ethyl-2-methyl-5-propyldecane

Provide an acceptable name for the alkane shown below.

hexane or n-hexane

Provide an acceptable name for the alkane shown below. CH3CH2CH2CH2CH2CH3

Bicyclo[2.1.1]hexane

Provide an acceptable name for the compound below.

4,4-dichloro-6-isopropyl-3-methylnonane

Provide an acceptable name for the following compound.

isobutylcyclopentane or (2-methylpropyl)cyclopentane

Provide an acceptable name for the following compound.

2,2,5-trimethylhexane

Provide the IUPAC name of (CH3)2CHCH2CH2C(CH3)3

3-ethylpentane

Provide the IUPAC name of (CH3CH2)3CH

2,3,6,7-tetramethylnonane

Provide the name of the compound below.

3-fluoro-2,2-dimethylhexane

Provide the name of the compound below.

sec-butylcycloheptane

Provide the name of the compound below.

2,2,7-trichloro-4-ethyl-6-isobutyl-7,10-dimethyldodecane

Provide the name of the compound shown.

n-alkanes

Straight-chain alkanes are also called ________.

E) torsion strain

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

C) fewer unfavorable steric factors in the twisted boat

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

E) 62

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

transannular strain

What element of ring strain exists in cyclooctane but not in cyclopropane?

E) methane

What is the major constituent of natural gas? A) octane B) butane C) propane D) ethane E) methane

C) 11

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

A) that n-hexane is less dense than water

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

B) propane and butane

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

B) cis-1,2-dimethylcyclopentane

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

van der Waals or London forces

Which intermolecular force is primarily responsible for the interactions among alkane molecules?

C

Which line angle drawing best represents the Newman Projection shown below?

C) III

Which line-angle formula corresponds to the chair conformation shown below? A) I B) II C) III D) IV

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.

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.

B) twist boat < boat < chair < half-chair

Which of the following correctly lists the conformations of cis-1,4-di-t-butylcylcohexane in order of increasing energy? A) chair < boat < twist boat < half-chair B) twist boat < boat < chair < half-chair C) chair < twist boat < half-chair < boat D) boat < chair < twisted boat < half-chair E) half-chair < chair < boat < twisted boat

D) chair < twist < boat < half-chair

Which of the following correctly lists the conformations of cyclohexane in order of increasing energy? A) chair < boat < twist < half-chair B) half-chair < boat < twist < chair C) chair < twist < half-chair < boat D) chair < twist < boat < half-chair E) half-chair < twist < boat < chair

B) cyclohexane < cyclopentane < cyclobutane < cyclopropane

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

A) cyclooctane

Which of the following cycloalkanes exhibits the greatest molar heat of combustion? A) cyclooctane B) cycloheptane C) cyclohexane D) cyclobutane E) cyclopropane

D) cyclohexane

Which of the following cycloalkanes has the smallest heat of combustion per CH2 group? A) cyclopropane B) cyclobutane C) cyclopentane D) cyclohexane E) cycloheptane

A) bridged bicyclic

Which of the following describes the compound below? A) bridged bicyclic B) fused bicyclic C) spiro bicyclic D) bridged tricyclic

C) cis 1,3-difluorocyclohexane

Which of the following difluorocyclohexane isomers has the greatest molecular dipole in its least stable chair conformation? A) cis 1,2-difluorocyclohexane B) trans 1,2-difluorocyclohexane C) cis 1,3-difluorocyclohexane D) trans 1,3-difluorocyclohexane

B

Which of the following is a bridged bicyclic alkane? A) cis-decalin B) bicyclo[2.2.1]heptane C) bicyclo[3.2.0]heptane D) bicyclo[4.1.0]heptane E) none of the above

E) The gauche and anti conformers differ primarily in the amount of nonbonded strain present.

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.

A) The methyl group at C-3 is equatorial.

Which of the following statements is a correct description of the most stable conformation of 1,1,3-trimethylcyclohexane? A) The methyl group at C-3 is equatorial. B) C-1 is a tertiary carbon and C-3 is a primary carbon. C) C-1 is a quaternary carbon and C-3 is a secondary carbon. D) C-1 is a tertiary carbon and C-3 is a secondary carbon. E) Both methyl groups at C-1 are equatorial.

C) The lowest energy conformation is one in which the bond angles are slightly less than 90° even though this increases angle strain.

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.

A) alkanes

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.

E) both A and C

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

A) The two chair conformations are equal in energy.

Which of the statements below correctly describes the chair conformations of A) The two chair conformations are equal in energy. B) The higher energy chair conformation contains two axial ethyl groups. C) The higher energy chair conformation contains two equatorial ethyl groups. D) The lower energy chair conformation contains two axial ethyl groups. E) The lower energy chair conformation contains two equatorial ethyl groups.

D) The higher energy chair conformation contains two axial methyl groups.

Which of the statements below correctly describes the chair conformations of A) The two chair conformations are of equal energy. B) The higher energy chair conformation contains one axial methyl group and one equatorial methyl group. C) The lower energy chair conformation contains one axial methyl group and one equatorial methyl group. D) The higher energy chair conformation contains two axial methyl groups. E) The lower energy chair conformation contains two axial methyl groups.

Alkanes are nonpolar and as such they do not dissolve to any appreciable extent in water.

Why are alkanes described as hydrophobic?

D) 2 < 1 < 3

With each structure below drawn in its most stable chair conformation, identify the sequence that ranks the structures in order of increasing stability. A) 1 < 2 < 3 B) 2 < 3 < 1 C) 3 < 1 < 2 D) 2 < 1 < 3

"Knocking" is the potentially damaging, premature explosive combustion of certain gasoline mixtures in a car's engine.

Within the context of commercial uses of alkanes, explain what "knocking" is.

Butane

________ is the n-alkane of greatest molecular weight which is a gas at room temperature and pressure.

Catalytic cracking

________ is the reaction process through which long-chain alkanes are converted into a mixture of short-chain alkanes and alkenes.