Q18P - Organic Chemistry (Mcmurry)

Question

Draw a Newman projection along the C2 -C3 bond of the following conformation of 2,3-dimethylbutane, and calculate a total strain energy:

Step-by-Step Solution

Answer

The total strain energy is 11.4 kJ mol.

Step 1: Newman Projection

Newman projections are important for understanding alkane stereochemistry. A chemical bond’s conformation from front part to back part can be visualized using Newman projection.

Step 2: Drawing the Newman projection and calculating the total strain energy

The confirmation given here is a staggered conformation and the hydrogens on carbons 2 and 3 are$60°$ apart.

The Newman projection exhibits three gauche interactions. Each of the interactions have an energy of 3.8 kJ/mol.

Newman projection of the molecule

 

The total strain energy of the molecule can be given as:

$\begin{array}{c}\text{Total strain energy=3×}\frac{\text{3.8 kJ}}{\text{mol}}\\ \text{=}\frac{\text{11.4 kJ}}{\text{mol}}\end{array}$