Increased substitution around a bond leads to increased strain. Take the four substituted butanes listed below, for example. For each compound, sight along the C2-C3 bond and draw Newman projections of the most stable and least stable conformations. Use the data in Table to assign strain energy values to each conformation. Which of the eight conformations is most strained?

Which is least strained?

(a) 2-Methylbutane

(b) 2, 2-Dimethylbutane

(c) 2, 3-Dimethylbutane

(d) 2, 2, 3-Trimethylbutane

Energy Costs for Interactions in Alkane Conformers Energy cost (kJ/mol) Cause Interaction (kcal/mol) Torsional strain Mostly torsional strain Torsional and steric strain Steric strain HOH eclipsed H+CH3 eclipsed CH3+CH3 eclipsed CH3+CH3 gauche 4.0 1.0 6.0 1.4 11 2.6 3.8 0.9