Question 1

Which of the following best explains why the staggered conformation of ethane is more stable than the eclipsed conformation?

Accepted Answer

The staggered conformation has less torsional strain due to minimized electron repulsion between C-H bonds.

Question 2

What is the energy difference between the staggered and eclipsed conformations of ethane?

Accepted Answer

$$12\ \mathrm{kJ/mol}$$

Question 3

Which of the following statements about the conformational analysis of butane is correct?

Accepted Answer

The anti conformation is the most stable due to minimized steric and torsional strain.

Question 4

Which type of strain is primarily responsible for the instability of cyclopropane?

Accepted Answer

Angle strain due to bond angles of $$60^\circ$$ and torsional strain from eclipsing hydrogens.

Question 5

Why does cyclohexane adopt a chair conformation rather than a planar structure?

Accepted Answer

The chair conformation eliminates both angle strain and torsional strain, making it the most stable.

Question 6

What is the main reason that the boat conformation of cyclohexane is less stable than the chair conformation?

Accepted Answer

The boat conformation has flagpole interactions and increased torsional strain.

Question 7

A methyl group is attached to cyclohexane. Which conformation is more stable and why?

Accepted Answer

The conformation with the methyl group in the equatorial position is more stable due to reduced 1,3-diaxial interactions.

Question 8

Which of the following best describes a ring flip in cyclohexane?

Accepted Answer

A process where axial substituents become equatorial and vice versa.

Question 9

Which conformation of trans-1,2-dibromocyclohexane is more stable?

Accepted Answer

The conformation where both bromine atoms are equatorial.

Question 10

What is the effect of increasing the size of a substituent on cyclohexane on the equilibrium between axial and equatorial conformers?

Accepted Answer

Larger substituents increasingly favor the equatorial position due to greater steric hindrance in the axial position.

Question 11

Which of the following statements about the heat of combustion of cycloalkanes is correct?

Accepted Answer

Cyclohexane has the lowest heat of combustion per $$\mathrm{CH}_2$$ group, indicating it is the most stable monocyclic alkane.

Question 12

Which of the following best describes the gauche interaction in butane?

Accepted Answer

A staggered conformation where the two methyl groups are $$60^\circ$$ apart, resulting in steric strain.

Question 13

Which of the following is NOT a source of ring strain in cycloalkanes?

Accepted Answer

Resonance stabilization.

Question 14

A chemist is analyzing the stability of isobutane and butane by measuring their heats of combustion. If butane releases more heat upon combustion than isobutane, what can be concluded?

Accepted Answer

Isobutane is more stable than butane.

Question 15

Which of the following is true regarding the energy barrier to rotation about the C–C bond in butane?

Accepted Answer

It is higher than in ethane due to steric interactions between methyl groups.

Question 16

Which conformation of cyclohexane is most commonly found at room temperature?

Accepted Answer

Chair conformation

Question 17

What is the dihedral angle between adjacent C-H bonds in the most stable conformation of ethane?

Accepted Answer

$$60^\circ$$

Question 18

Which of the following best explains why the equatorial position is favored for large substituents on cyclohexane?

Accepted Answer

The equatorial position minimizes steric interactions with axial hydrogens (1,3-diaxial interactions).

Conformational Analysis of Acyclic Alkanes and Cyclohexanes

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