Final answer:
The staggered Newman projection with a 180° torsional angle between the carbon atoms has the lowest energy in heptane.
Step-by-step explanation:
A Newman projection is a way to visualize the conformation (arrangement of atoms) of a molecule. It displays the molecule from the point of view of one of the carbon-carbon (C-C) bonds, with the front carbon represented by a dot and the back carbon represented as a circle.
The staggered Newman projection has the lowest energy because it minimizes steric repulsion between the substituents (atoms or groups) attached to the carbons.
In the case of heptane, which has seven carbon atoms, there are multiple possible staggered Newman projections. The one with the lowest energy has the substituents as far apart as possible, which corresponds to a 180° torsional angle between the carbon atoms. This conformation is called the anti-conformation.
In summary, the staggered Newman projection with a 180° torsional angle between the carbon atoms has the lowest energy in heptane.