Potential energy and Newman projections

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Because of the free rotation about the C-C bond, 1-bromopropane exists in many conformations (conformers).

Drawing Conformations
There are three common ways of drawing conformations:
1] Wedges
2] Newman Projections
3] Sawhorse Structures
The most common Newman Projections are as below.

Newman Projections
The molecule is drawn as if it is viewed straight down the C-C bond.
Figure

The front carbon is drawn with 3 bonds in a Y shape
The back carbon is drawn as a circle (O) with 3 bonds pointing out from it.

1-bromopropane can adopt four important conformations.
1] Totally Eclipsed (A)
2] Gauche (B)
3] Partially Eclipsed (C)
4] Anti (D)
Now  represents the angle between the C-CH3 ...