NewmanProjektionen

Newman projections are a representation method in organic chemistry for visualizing the spatial arrangement of substituents around a carbon–carbon single bond. They simplify the three-dimensional structure by looking directly along the bond: the front carbon is drawn as a point with its three substituents arranged at 120-degree intervals, and the back carbon is shown behind it with its three substituents likewise arranged. In this view, the dihedral angles between front and back substituents correspond to the torsional orientation of the bond.

In a Newman projection, the most common conformations are staggered and eclipsed. The eclipsed conformation occurs when substituents on the two carbons align, corresponding to a dihedral angle of 0 degrees and generally higher torsional strain. The staggered conformation occurs when the front and back substituents are offset by 60 degrees, typically more stable. Within staggered forms, chemists often distinguish anti arrangements, where large groups are opposite each other, from gauche arrangements, where they are 60 degrees apart. The relative energies of these conformations arise from torsional strain in eclipsed forms and steric interactions between bulky substituents.

Newman projections are widely used to analyze conformational preferences of open-chain alkanes and substituted alkanes, helping to explain reactivity and reaction rates in terms of accessible conformations. They can also be applied to certain substituted cycloalkanes along a chosen C–C bond. However, the projection can be less intuitive for complex, highly substituted molecules, and other representations may be preferred for a fuller three-dimensional picture. The method is named after chemist Melvin Newman.