# 1.3: Conformational Analysis Practice Exercises

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1) Draw a Newman projection of the most stable conformation of 2-methylpropane.

2) The structures below are:

A) not isomers.

B) conformational isomers.

C) cis-trans isomers.

D) structural isomers.

E) both B and D

3) Define the term conformation.

4) View a butane molecule along the C2-C3 bond and provide a Newman projection of the lowest energy conformer.

5) Provide a representation of the gauche conformer of butane.

6) 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

7) Which of the following cycloalkanes exhibits the greatest molar heat of combustion per CH2 group?

A) cyclooctane B) cycloheptane C) cyclohexane D) cyclobutane E) cyclopropane

8) Which of the following correctly ranks the cycloalkanes in order of increasing ring strain per methylene (CH2 group)?

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

9) Describe the source of angle strain and torsional strain present in cyclopropane.

10) 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.

11) Draw the most stable conformation of trans-1,2-dimethylcyclohexane.

12) Draw the most stable conformation of cis-1,2-dimethylcyclohexane.

13) Which of the statements below correctly describes the chair conformations of trans-1,4- dimethylcyclohexane?

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.

14) Which of the statements below correctly describes the chair conformations of trans-1,3- diethylcyclohexane.

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.

15) Draw the most stable conformation of trans-1-tert-butyl-3-ethylcyclohexane.

16) 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

17) The energy difference between the axial and equatorial conformers of methylcyclohexane is:

A) < 0.1 kcal/mol B) 0.9 kcal/mol C) 1.7 kcal/mol D) 2.5 kcal/mol E) > 5.0 kcal/mol

18) Draw the most stable conformation of cis-1-ethyl-3-methylcyclohexane.

19) Draw the most stable conformation of cis-1-ethyl-4-isopropylcyclohexane.

20) From the perspective of viewing down the C2-C3 bond, draw the Newman projection of the most stable conformation of 2,3-dimethylbutane.

21) 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

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

23) 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

This page titled 1.3: Conformational Analysis Practice Exercises is shared under a not declared license and was authored, remixed, and/or curated by Sergio Cortes.