Which of the following diagrams correctly represents a Newman projection for propane when viewed along the $C_1–C_2$ bond?

• A. A Fischer projection with vertical and horizontal lines representing bonds.
• B. A circle with three bonds radiating from the center (front carbon) and three bonds radiating from behind the circle (back carbon), each attached to either $H$ or $\mathrm{CH}{3}_3$ groups.
• C. A zig-zag line structure showing all carbon and hydrogen atoms in a flat plane.
• D. A chair conformation diagram with alternating up and down substituents.

Answer: (B)

Verified step by step guidance

1. Identify the bond along which the Newman projection is to be viewed. Here, it is the bond between carbon 1 (C1) and carbon 2 (C2) in propane.
2. Recall that a Newman projection represents the spatial arrangement of substituents around two adjacent carbons by looking straight down the bond connecting them. The front carbon is depicted as a dot or small circle, and the back carbon as a larger circle behind it.
3. For propane, C1 is bonded to three hydrogens (H) and C2 is bonded to two hydrogens and one methyl group (CH3). In the Newman projection, the front carbon (C1) will have three bonds radiating from the center, each to a hydrogen atom.
4. The back carbon (C2) will be represented by a circle behind the front carbon, with three bonds radiating from it: two to hydrogens and one to the methyl group (CH3). These bonds are staggered or eclipsed depending on the conformation, but the key is that all substituents are shown radiating from the two carbons.
5. Compare the given options: a Fischer projection uses vertical and horizontal lines and is not a Newman projection; a zig-zag line structure shows a planar view, not a Newman projection; a chair conformation is specific to cyclohexane rings and not applicable here. The correct Newman projection is the one with a circle and three bonds radiating from both front and back carbons, showing hydrogens and the methyl group.