Question 1

Which of the following best describes the difference between the staggered and eclipsed conformations of ethane?

Accepted Answer

Staggered conformation has lower potential energy due to minimized electron repulsion, while eclipsed conformation has higher potential energy due to torsional strain.

Question 2

In a Newman projection of butane, what is the dihedral angle between the two methyl groups in the anti conformation?

Accepted Answer

$$180^\circ$$

Question 3

Which type of strain is primarily responsible for the higher energy of the eclipsed conformation in ethane?

Accepted Answer

Torsional strain

Question 4

Cyclopropane has significant angle strain because its bond angles are forced to be $$60^\circ. $$What is the ideal tetrahedral bond angle for sp$$^3$$ hybridized carbon atoms?

Accepted Answer

$$109.5^\circ$$

Question 5

Which conformation of cyclohexane is the most energetically favored (most stable)?

Accepted Answer

Chair

Question 6

What is the main reason that cyclobutane has less torsional strain than cyclopropane?

Accepted Answer

Cyclobutane can adopt a puckered conformation, reducing eclipsing of bonds.

Question 7

Which of the following best describes steric strain?

Accepted Answer

Strain caused by nonbonded atoms being forced closer together than their van der Waals radii allow.

Question 8

In butane, which conformation has the highest potential energy?

Accepted Answer

Eclipsed (with both methyl groups aligned)

Question 9

What is the formula for the internal angle of a regular polygon with $$n$$ sides?

Accepted Answer

$$180^\circ - \frac{360^\circ}{n}$$

Question 10

Which statement about the chair conformation of cyclohexane is TRUE?

Accepted Answer

It has no angle or torsional strain.

Question 11

A molecule of trans-1,4-dimethylcyclohexane in the chair conformation will have its methyl groups in which positions?

Accepted Answer

One axial and one equatorial

Question 12

Which type of strain is minimized in the chair conformation of cyclohexane?

Accepted Answer

Angle strain

Question 13

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

Accepted Answer

$$60^\circ$$

Question 14

Which of the following is NOT a consequence of angle strain in small cycloalkanes?

Accepted Answer

All atoms are in the same plane.

Question 15

Which conformation of butane is most stable and why?

Accepted Answer

Anti, because methyl groups are $$180^\circ$$ apart, minimizing steric repulsion.

Question 16

Which of the following best explains why cyclopentane adopts a non-planar conformation?

Accepted Answer

To minimize angle and torsional strain.

Question 17

What is the main difference between torsional strain and steric strain?

Accepted Answer

Torsional strain is due to eclipsing of bonds, while steric strain is due to nonbonded atoms being forced close together.

Question 18

Which of the following cycloalkanes has the least angle strain?

Accepted Answer

Cyclohexane

Question 19

In the chair conformation of cyclohexane, what is the orientation of the axial substituents?

Accepted Answer

Pointing straight up or down, perpendicular to the ring

Question 20

Which of the following statements about the boat conformation of cyclohexane is correct?

Accepted Answer

It has significant steric and torsional strain.

Conformations and Strain in Cyclic and Acyclic Organic Molecules

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