Deck 4: Organic Compounds: Cycloalkanes and Their Stereochemistry

Question 1

Provide the proper IUPAC name for the compound below.

Answer 1

trans-1-tert-butyl-4-ethylcyclohexane or trans-1-(1,1-dimethylethyl)-4-ethylcyclohexane

Question 2

For each disubstituted cyclohexane below, draw its ring-flip isomer. Circle the most stable conformation and label the substituent groups as axial or equatorial.
Draw and label:

Answer 2

conformations are of equal stability

Question 3

Which of the following cycloalkanes has the most ring strain?

A) cyclopropane
B) cyclobutane
C) cyclopentane
D) cyclohexane

Answer 3

cyclopropane

Question 4

Which of the following structures represents trans-1,3-dimethylcyclohexane?

A)

B)

C)

D)

Question 5

Substitution of which of the following groups on a cycloalkane would result in the greatest amount of steric strain?

A) bromo
B) ethyl
C) isopropyl
D) hydroxyl

Question 6

Refer to the structure below to answer the following question(s).
Refer to instructions. Which of the labeled groups is trans to b?

Question 7

If the 1,3-diaxial strain for an ethyl group is 4.0 kJ/mol, what is the energy difference between the axial and equatorial conformations of ethylcyclohexane?

A) 2.0 kJ/mol
B) 4.0 kJ/mol
C) 8.0 kJ/mol
D) 16.0 kJ/mol
E) Cannot be determined from the 1,3-diaxial strain

Question 8

Refer to the structure below to answer the following question(s).
Refer to instructions. Which of the labeled groups in the structure are equatorial?

Question 9

If cyclohexane were planar, how much torsional strain would be present in the planar molecule? Assume that the energy cost for each H↔H eclipsing interaction is 4.0 kcal/mol.

A) 12.0 kJ/mol
B) 24.0 kJ/mol
C) 36.0 kJ/mol
D) 48.0 kJ/mol
E) 64.0 kJ/mol

Question 10

Refer to the structure below to answer the following question(s).
Refer to instructions. Which groups have a 1,3-diaxial interaction with each other?

Question 11

In which of the following compounds would the carbon−carbon bond angle diverge the greatest from 109°?

A) cyclodecane
B) cyclooctane
C) cyclopentane
D) cyclopropane

Question 12

In cycloheptane, which of the following factors contributes the least to the stability of the ring conformation?

A) torsional strain
B) angle strain
C) steric strain
D) all of these contribute to an approximately equal degree

Question 13

What is the energy difference between the two chair conformations of the following compound that is due to steric strain? cis-1-bromo-4-isopropylcyclohexane
Assume the following 1,3-diaxial strains.
Br: 1.0 kJ/mol
CH(CH₃)₂: 4.6 kJ/mol

A) 7.2 kJ/mol
B) 5.6 kJ/mol
C) 9.2 kJ/mol
D) 11.2 kJ/mol

Question 14

For each disubstituted cyclohexane below, draw its ring-flip isomer. Circle the most stable conformation and label the substituent groups as axial or equatorial.
Draw and label:

Question 15

Label each pair of compounds below as:
Label: and

Question 16

For each pair of molecules below, circle the most stable. and

Question 17

Which of the following cycloalkanes would be the most similar to its open chain counterpart?

A) cyclodecane
B) cyclooctane
C) cyclopentane
D) cyclopropane

Question 18

The following is an incorrect name according to IUPAC nomenclature rules. Correct it such that it is a proper IUPAC name.
3-methylhexylcyclopentane

Question 19

Label each pair of compounds below as:
Label: and

A)identical
B)stereoisomers
C)constitutional isomers
D)identical, but differing in conformation
Where stereoisomers are present, label the isomers as cis and trans.

Question 20

Draw and name the seven constitutional isomers for cycloalkane, C₆H₁₂.

Question 21

Which one of the following structures represents a different compound from the other three?

A)

B)

C)

D)

Question 22

Which of the following compounds can adopt a chair conformation in which there are no axial methyl groups?

A) 1,1-dimethylcyclohexane
B) cis-1,2-dimethylcyclohexane
C) trans-1,2-dimethylcyclohexane
D) trans-1,3-dimethylcyclohexane

Question 23

(−)-Menthol is responsible for the characteristic flavor and taste of peppermint. The structure of (−)-menthol is shown below. Use this information to answer the following question.
Refer to instructions. On the chair template provided below, draw the two chair conformations that are in equilibrium for (−)-menthol.

Question 24

Which one of the following structures represents a different compound from the other three?

A)

B)

C)

D)

Question 25

Which of the following is the most stable conformation of cis-1-isopropyl-3-methylcyclohexane?

A)

B)

C)

D)

Question 26

Which of the following is the most stable conformation of trans-1-ethyl-3-methylcyclohexane?

A)

B)

C)

D)

Question 27

D-Pinitol is an interesting hexahydroxycyclohexane, whose structure is shown below. On the templates provided, draw the two chair conformations that are in equilibrium for D-pinitol. Circle the most stable conformation.

Question 28

Which of the following statements is not true regarding the conformation of substituted cyclohexanes?

A) ring flip of substituted cyclohexanes flips the axial and equatorial positions of substituents
B) substituted cyclohexanes are destabilized by 1,3-diaxial interactions
C) the twist-boat conformation of cyclohexane is more stable than the chair conformation
D) the relative amount of two conformations of substituted cyclohexanes can be determined from the difference in strain energy

Question 29

Which of the following structures represents trans-1,2-dimethylcyclohexane?

A)

B)

C)

D)