Newman Projections Practice Problems

Consider the following pairs of conformations. 

Identify which conformation has the lowest strain energy.

Identify the more stable conformation. If they are equally stable, write "no difference".

Identify the marked dihedral angle in the given Newman projection.

Draw a potential energy diagram for the conformational analysis of n-butane as it rotates around the single bond between C2 and C3.

Hint: One C—H bond eclipsed with another C—H bond contributes to 4.2 KJ/mol, one C—H bond eclipsed with a C—CH₃ bond contributes 5.4 KJ/mol while One C—CH₃ bond eclipsed with a C—CH₃ bond contributes 13 KJ/mol to torsional energy. Similarly, Gauche (60° methyl group) will add 3.8 KJ/mol energy.

The chair conformation of bromocyclohexane with the bromo substituent in an axial position is about 0.43 kcal/mol more stable compared to the conformation with the bromo substituent in an equatorial position. Determine how much more stable the anti-conformation of 1-bromopropane is than its gauche conformation. (Rotate about C1-C2 bond)

Construct a potential energy graph for n-pentane as it rotates about the bond between C2 and C3. Start with a 0° dihedral angle and rotate the front carbon.

Table:

Draw potential energy vs dihedral angle graph for conformational analysis of propane as it rotates around the single bond between C1 and C2. Also, draw the Newman projections for each eclipsed and staggered conformation and show the dihedral angles.

Hint: One C—H bond eclipsed with another C—H bond contributes to 4.2 KJ/mol torsional energy. One C—H bond eclipsed with a C—CH₃ bond contributes to 5.4 KJ/mol torsional energy.

Based on the given pair of conformations, predict which conformation is expected to be more favored at equilibrium.

Identify the most stable conformation of isobutyl bromide among the following.

What is the dihedral angle for the given Newman projection?

A reaction coordinate diagram is a plot of potential energy versus the progress of a reaction. Which structure is located at the top of the hill if the given reaction coordinate diagram shows the conversion of conformation A to conformation B?

Which conformation is the least stable and most stable?

True or False: The conformation shown has a 120-degree dihedral angle for the involved groups (Cl groups).

Determine the more stable of the given conformation pair. If the number of their gauche interactions is the same, select the one with the interaction between smaller groups.

Which is the more stable conformation from the given pair? In the case that both have equal gauche interactions, select the one with the interaction between smaller groups.

Determine structures that correspond to the same compound. Also identify structures that correspond to different compounds.

Does the following graph correctly represent the torsional energy of 2-methylpentane along the C3-C4 bond? (Note: C4 is in the black, represented by a circle with three bonds extending from it, while C3 is in the front, represented by three bonds forming a Y shape. The angle between the isopropyl group on the front carbon and the methyl group on the back carbon is referred to as the dihedral angle.)

What is the value of the specified dihedral angle (θ) for the following conformation?