Q.3-3-15P - Organic Chemistry (Mcmurry)

Question

Question: Make a graph of potential energy versus angle of bond rotation for propane,and assign values to the energy maxima.

Step-by-Step Solution

Answer

Answer

The graph of potential energy versus angle of bond rotation can be drawn as shown below.

Step 1: Graph of potential energy versus angle of bond rotation

A torsional strain is present in the eclipsed conformation of a particular isomer. The boundary to this rotation that is created from the strain is indicated using a graph of potential energy vs. the rotation angle.

Step 2: The graph of potential energy versus angle of bond rotation for propane

Experiments indicate that there is a 14 $KJ/mol$ barrier to rotation in propane. The most stable conformer is the one where all the bonds are situated away from each other (staggered). The least stable is the eclipsed conformation.

In the eclipsed conformer, the six bonds (five C-H and one C-C) are located close to each other for any two carbon atoms located adjacent to each other. Here, the energy value is 6 $KJ/mol$ to the C-C/C-H eclipsing interaction.

                                              Energy diagram