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Introduction

A Newman projection is a graphical method that offers a detailed perspective of a molecule’s 3D structure, typically focusing on a carbon-carbon bond. It’s an effective tool for visualizing the stereochemistry of alkanes. The projection displays the conformation of a chemical bond from front to back, with the front atom depicted as a point where three lines intersect and the back atom represented as a circle. This representation provides a clear view of the dihedral angle between the front and back atoms.

 

Summary:

  • A Newman projection is a diagram which represents the perspective of looking down a specified bond

  • The atom in front, closer to the observer, is denoted as the intersection point of 3 lines

  • The atom in the back is denoted as a circle

Newman Projection Diagram 1

Another perspective:

Newman Projection Diagram 2
Newman Projection Diagram 3

Conformations and Stability

Given the free rotation around single bonds, a molecule can adopt various conformations. For any given chemical bond, up to six distinct conformations can be illustrated. These conformations are obtained by rotating either the front or back atom by 60 degrees. Among these six conformations, three will be staggered, and the remaining three will be eclipsed. These conformations can be plotted on a relative energy diagram, as if often shown for ethane and butane.

In a staggered projection, the surrounding substituents, or fragments, appear equidistant from each other. This conformation can experience both anti and gauche interactions. Anti interactions occur when substituents are positioned exactly opposite each other at 180° in the Newman projection. Gauche interactions occur when substituents are 60° apart in a Newman projection. Anti interactions experience less steric strain than gauche interactions, but both experience less steric strain than the eclipsed conformation.

An eclipsed projection gives the impression that the surrounding species are almost superimposed. In reality, these species are aligned but are depicted slightly staggered for clarity on paper. These conformations are generally higher in energy due to increased bond strain. However, this strain can be somewhat mitigated if a hydrogen is eclipsed over a larger species, as opposed to two large species eclipsed over each other.

Butane Conformations Diagram

Keywords

Newman Projection | Conformation | Conformer | Butane Conformation | Staggered | Eclipsed | Gauche

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