For each of the following compounds, predict the energy barrier to rotation (looking down any one of the C-C bonds). Draw a Newman projection and then compare the staggered and eclipsed conformations. Remember that we assigned 4 kJ/mol to each pair of eclipsing H’s and 6 kJ/mol to an H eclipsing a methyl group:

(a) 2,2-Dimethylpropane

(b) 2-Methylpropane