Q: What is the dihedral angle ($$\theta) in $$the anti conformation of butane, and why is this conformation particularly stable?

$$\theta = 180^\circ$$; because the methyl groups are opposite each other, minimizing steric and torsional strain.

Question 1

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

Accepted Answer

Staggered conformation minimizes torsional strain by maximizing the distance between adjacent C-H bonds.

Question 2

Given the energy diagram for ethane, what is the energy difference between the staggered and eclipsed conformations?

Accepted Answer

$$12.6\ \mathrm{kJ/mol}$$

Question 3

What is the dihedral angle ($$	heta) in $$the anti conformation of butane, and why is this conformation particularly stable?

Accepted Answer

$$	heta = 180^\circ$$; because the methyl groups are opposite each other, minimizing steric and torsional strain.

Question 4

Which type of strain is present in the eclipsed conformation of ethane?

Accepted Answer

Torsional strain only

Question 5

In the Newman projection of butane, which conformation has the highest potential energy?

Accepted Answer

Eclipsed with methyl groups aligned

Question 6

If you replace a hydrogen atom with a bromine atom in ethane, how does this affect the energy difference between staggered and eclipsed conformations?

Accepted Answer

The energy difference increases due to greater steric and torsional strain from the larger bromine atom.

Question 7

Which of the following best describes the gauche conformation of butane?

Accepted Answer

A staggered conformation with methyl groups $$60^\circ$$ apart, resulting in steric strain.

Question 8

Which of the following is true regarding the potential energy of ethane as a function of dihedral angle?

Accepted Answer

Potential energy is highest at $$0^\circ ($$eclipsed) and lowest at $$60^\circ ($$staggered).

Question 9

A molecule of butane is shown in a Newman projection with the two methyl groups $$180^\circ$$ apart. What type of strain is minimized in this conformation?

Accepted Answer

Both torsional and steric strain

Question 10

Which of the following best describes the relationship between dihedral angle and torsional strain in ethane?

Accepted Answer

Torsional strain is minimized at staggered conformations ($$60^\circ$$, $$180^\circ$$, etc.) and maximized at eclipsed conformations ($$0^\circ$$, $$120^\circ$$, etc.).

Question 11

Which conformation of butane is most likely to be observed at room temperature due to its low energy?

Accepted Answer

Staggered anti

Question 12

A chemist is analyzing a molecule using a Newman projection and observes that two large groups are $$60^\circ$$ apart. What type of strain is present in this conformation?

Accepted Answer

Steric strain due to gauche interaction

Question 13

Which of the following is a correct statement about torsional strain?

Accepted Answer

Torsional strain arises from the repulsion between atoms three bonds apart in an eclipsed conformation.

Question 14

In a real-world scenario, why might the presence of bulky substituents (such as tert-butyl groups) on a carbon chain affect the observed conformations?

Accepted Answer

Bulky substituents favor staggered anti conformations to minimize steric interactions.

Question 15

A patient is exposed to a drug molecule that contains a butane backbone. Which conformation of the butane backbone is most likely to interact favorably with a receptor due to minimized strain?

Accepted Answer

Staggered anti

Question 16

Which of the following best describes the process of rotating a Newman projection about a central axis?

Accepted Answer

Rotation changes the dihedral angle, altering the observed conformation and potential energy.

Question 17

If the dihedral angle in ethane is increased from $$0^\circ to$$ $$60^\circ$$, what happens to the potential energy?

Accepted Answer

Potential energy decreases.

Question 18

Which conformation of butane is associated with both torsional and steric strain?

Accepted Answer

Eclipsed with methyl groups aligned

Question 19

A molecule is shown in a Newman projection with all hydrogens eclipsed. What is the dihedral angle and what type of strain is present?

Accepted Answer

$$	heta = 0^\circ$$; torsional strain

Conformational Analysis of Alkanes: Ethane and Butane

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