4. Alkanes and Cycloalkanes

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

Draw a graph, similar to Figure 3-9, of the torsional strain of 2-methylpropane as it rotates about the bond between C1 and C2. Show the dihedral angle and draw a Newman projection for each staggered and eclipsed conformation.

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

(a)

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

(c)

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

(a)

(b)

(c)

Choose the conformation in each pair that is most stable. If both are equally stable, then write 'no difference.'

(a)

In Chapter 5, we introduce reaction coordinate diagrams as a plot of potential energy versus the progress of a reaction. Consider the reaction coordinate diagram drawn for the 'reaction' of conformation A becoming conformation B. Which structure is present at the top of the hill?

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

(c)

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).

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

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)

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)

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

(f)

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

(c)