(How to manipulate JSmol structures)
Ethane
The difference in energy between the staggered and eclipsed conformation of ethane is 3.0 kcal/mol. The staggered conformation (dihedral angles = 60o) is more stable than the eclipsed conformation (dihedral angles = 0o). Thus, each pair of eclipsed C-H bond is worth 1.0 kcal/mol. [Eclipsed hydrogens in the graph are shown in the graph in red. The dihedral angle is shown as non-zero for illustrative purposes.]
Measure the C-C-H bond angle in the JSmol structure. Why is it slightly greater than the H-C-H bond angle in methane? Measure the H-C-H bond angle in staggered ethane. Why is it slightly smaller than the H-C-H bond angle in methane? If you are finished, advance to propane.
