4. Alkanes and Cycloalkanes

Construct a graph, similar to Figure 3-11, of the torsional energy of 3-methylpentane along the C2―C3 bond.

e. Indicate which conformations are the most stable (lowest energy) and the least stable (highest energy).

Which of the following best describes the most stable Newman projection for 2,3-dimethylpentane when viewed down the C$2_{-}$C$3_{}$ bond?

Given the staggered conformation of $C_2{H}_6$ (ethane), which of the following correctly matches the front and back substituents in a Newman projection looking down the $C–C$ bond?

Construct a graph, similar to Figure 3-11, of the torsional energy of 3-methylpentane along the C2―C3 bond.

a. Place C2 in front, represented by three bonds coming together in a Y shape, and C3 in back, represented by a circle with three bonds pointing out from it.

b. Define the dihedral angle as the angle between the methyl group on the front carbon and the ethyl group on the back carbon.

For each pair of conformations shown, choose which is most stable. [If both conformations have the same number of gauche interactions, choose the one where the interactions are between smaller groups.]

(f)

Construct a graph, similar to Figure 3-11, of the torsional energy of 3-methylpentane along the C2―C3 bond.

c. Begin your graph at the 0° dihedral angle and begin to turn the front carbon.

For each of the pairs in Assessment 3.29, which conformation would you expect to be more prominent at equilibrium?

(a)

(b)

(c)

Which of the following structures represent the same compound? Which ones represent different compounds?

(f)

For each pair of conformations shown, choose which is most stable. [If both conformations have the same number of gauche interactions, choose the one where the interactions are between smaller groups.]

(e)

Which conformation in each of the following pairs has the least strain energy?

(c)

Calculate the dihedral angle (θ) for the conformations shown.

(c)

Why is it incorrect to say that the dihedral angle shown is 120° or even 109°?

Draw a graph, similar to Figure 3-11, of the torsional energy of 2-methylbutane as it rotates about the C2—C3 bond.

Which of the following conformers of isobutyl chloride is the most stable?