Conformations of Ethane & Butane Simulation

Conformations are the different shapes a molecule takes as it rotates about a single bond. In ethane the staggered conformation, with the C–H bonds of the two carbons as far apart as possible, is about 12 kJ/mol lower than the eclipsed one; that energy is torsional strain. Butane adds steric strain between the two methyl groups: the anti form (180°) is lowest, gauche (60°) about 3.8 kJ/mol higher, the partially eclipsed form (120°) about 16 and the fully eclipsed form (0°) about 19 kJ/mol.

This conformations simulation for ethane and butane turns the C–C bond and moves three pictures together: a 3D model (or a Sawhorse projection), the Newman projection and the potential-energy curve, with the current conformation named and the distance between the two methyl groups shown. Press a named conformation to jump to it or press Play to spin the bond. A third tab shows the exception students get asked about: in ethane-1,2-diol the gauche form is more stable than anti, because the two OH groups are close enough to hydrogen-bond.