CONFORMATIONAL ANALYSIS – PRACTICE EXERCISES

1 CONFORMATIONAL ANALYSIS PRACTICE EXERCISES1) Draw a newman projection of the most stable conformation of ) The structures below are:HHHHCH3CH3 HCH3 HHHCH3A) not ) CONFORMATIONAL ) cis-trans ) structural ) both B and D3) Define the term ) View a butane molecule along the C2-C3 bond and provide a newman projection of the lowest ) Provide a representation of the gauche conformer of ) Among the butane conformers, which occur at energy minima on a graph of potential energy versusdihedral angle?A) gauche onlyB) eclipsed and totally eclipsedC) gauche and antiD) eclipsed onlyE) anti only7) Which of the following cycloalkanes exhibits the greatest molar heat of combustion per CH2 group?

2 A) cyclooctane B) cycloheptane C) cyclohexane D) cyclobutane E) cyclopropane8) Which of the following correctly ranks the cycloalkanes in order of increasing ring strain per methylene(CH2 group)?A) cyclopropane < cyclobutane < cyclohexane < cyclopentaneB) cyclohexane < cyclopentane < cyclobutane < cyclopropaneC) cyclohexane < cyclobutane < cyclopentane < cyclopropaneD) cyclopentane < cyclopropane < cyclobutane < cyclohexaneE) cyclopropane < cyclopentane < cyclobutane < cyclohexane9) Describe the source of angle strain and torsional strain present in ) Which of the following statements is a correct description of the most stable conformation of 1,1,3-trimethylcyclohexane?

3 A) The methyl group at C-3 is ) C-1 is a tertiary carbon and C-3 is a primary ) C-1 is a quaternary carbon and C-3 is a secondary ) C-1 is a tertiary carbon and C-3 is a secondary ) Both methyl groups at C-1 are ) Draw the most stable conformation of trans-1, ) Draw the most stable conformation of cis-1, ) Which of the statements below correctly describes the chair conformations of trans-1,4-dimethylcyclohexane?A) The two chair conformations are of equal ) The higher energy chair conformation contains one axial methyl group and one equatorialmethyl ) The lower energy chair conformation contains one axial methyl group and one equatorial ) The higher energy chair conformation contains two axial methyl ) The lower energy chair conformation contains two axial methyl ) Which of the statements below correctly describes the chair conformations of trans-1, ) The two chair conformations are equal in ) The higher energy chair conformation contains two axial ethyl )

4 The higher energy chair conformation contains two equatorial ethyl ) The lower energy chair conformation contains two axial ethyl ) The lower energy chair conformation contains two equatorial ethyl ) Draw the most stable conformation of ) Which of the following correctly lists the conformations of cyclohexane in order of increasing energy?A) chair < boat < twist < half-chairB) half-chair < boat < twist < chairC) chair < twist < half-chair < boatD) chair < twist < boat < half-chairE) half-chair < twist < boat < chair17) The energy difference between the axial and equatorial conformers of methylcyclohexane is.

5 A) < kcal/mol B) kcal/mol C) kcal/mol D) kcal/mol E) > kcal/mol18) Draw the most stable conformation of ) Draw the most stable conformation of ) From the perspective of viewing down the C2-C3 bond, draw the newman projection of the most stableconformation of 2, ) In the lowest energy chair conformation of cis-1,3-dimethylcyclohexane, how many axial positions areoccupied by hydrogen atoms?A) 2 B) 3 C) 4 D) 5 E) 622) Arrange the following conformers of butane in order of energy, lowest to highest: eclipsed, totallyeclipsed, gauche, and ) In the lowest energy conformation of the compound below, how many alkyl substituents are axial?

6 CH3A) 0 B) 1 C) 2 D) 3 E) 6 ANSWERS1)HHHHCH3CH32) D3) Conformations are different arrangements of the same molecule formed by rotations about single )CH3 HHHHCH35)HCH3 HHHCH36) C 7) E cyclopropane, due to its high ring ) B9) The angle strain arises from the compression of the ideal tetrahedral bond angle of to 60 o. The largetorsional strain occurs since all C-H bonds on adjacent carbons are ) A11)CH3CH312)CH3CH313) D 14) A15)CH2CH3or16) D 17) C (see table 3-6 in the textbook)18)19)20)CH3CH3HH3 CHCH321) E 22) anti < gauche < eclipsed < totally eclipsed23) A all alkyl groups are (e)(e)(e)The most stable conformation has to be a chairand the bulkiest group (isopropyl) has to be ethyl group has to be cis to isopropyl, and the methyl group has to be trans to ethyl.