SolutionsSubstituted Cyclohexanes

Which of the following statements is correct regarding the most stable conformation expected for 1,1,3-trimethylcyclohexane?

A) The methyl group at C-3 is equatorial
B) C-1 is a tertiary carbon and C-3 is primary
C) C-1 is a quaternary carbon and C-3 is secondary
D) The methyl group at C-3 is axial
E) Of the two methyl groups at C-1, one is axial and the other equatorial
F) Both methyls at C-1 are equatorial

A) The methyl group at C-3 is equatorial
E) Of the two methyl groups at C-1, one is axial and the other equatorial

Draw the most stable conformer of trans-1,2-dimethylcyclohexane. And that of its cis isomer? Try drawing them in Newman projection.

Solution: most stable chairs of trans- and cis-1,2-dimethylcyclohexane, also in Newman projection

Which of the following statements describes the chair conformations of trans-1,4-dimethylcyclohexane?

A) The two chair forms are equal in energy
B) The chair with the highest energy contains a methyl group in axial and another in equatorial
C) The lower energy chair contains a methyl group in axial and another in equatorial
D) The most unstable conformer is a chair with two methyls in axial
E) The least unstable chair rotamer has two methyl groups at equatorial

D) The most unstable conformer is a chair with two methyls in axial
E) The least unstable chair rotamer has two methyl groups at equatorial

Which of the following statements describes the chair conformations of trans-1,3-diethylcyclohexane?

A) The two chair forms are equal in energy
B) The chair with the highest energy contains an ethyl group in axial and another in equatorial
C) The lower energy chair contains an ethyl group in axial and another in equatorial
D) The most unstable conformer is a chair with two ethyls in axial
E) The least unstable chair rotamer has two ethyl groups in equatorial

A) The two chair forms are equal in energy
B) The chair with the highest energy contains an ethyl group in axial and another in equatorial

Draw the most stable conformation of trans-1-tert-butyl-3-phenylcyclohexane

Solution: trans-1-tert-butyl-3-phenylcyclohexane prefers the tert-butyl group equatorial

The energy difference between the equatorial and axial chair forms of methylcyclohexane is:

A) < 0.1 kcal/mol
B) 3 kcal/mol
C) 0.9 kcal/mol
D) 1.8 kcal/mol
E) > 5 kcal/mol

D) 1.8 kcal/mol

Draw the conformational equilibrium of cis-1-phenyl-3-methoxycyclohexane in a Newman projection. Do you have any doubts about which conformation is the most stable?

Solution: conformational equilibrium of cis-1-phenyl-3-methoxycyclohexane in Newman projection

Draw in Newman projection the conformational equilibrium of trans-1-phenyl-3-methoxycyclohexane. Try to predict which conformation is the most stable.

Solution: conformational equilibrium of trans-1-phenyl-3-methoxycyclohexane in Newman projection

In the lowest energy conformation of the indicated compound, how many alkyl substituents are in axial?

Solution: in the most stable chair the three alkyl substituents are equatorial

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