Q16 P-d. - Organic Chemistry (Mcmurry)

Question

Sight along the C2-C1 bond of 2-methylpropane (isobutane). 

 

(d) Assign relative values to the maxima and minima in your graph, given that

An eclipsing interaction costs 4.0 kJ/mol and an $\mathbf{H}\leftrightarrow {\mathbf{CH}}_{\mathbf{3}}$ eclipsing

Interaction costs 6.0 kJ/mol.

Step-by-Step Solution

Answer

(d)

Eclipsed and staggered conformation

The conformation comprising a significant stability is the staggered conformation. A molecule having staggered conformation as stable does not indicate the molecule only maintains a staggered conformation.

Assigning values to the maxima and minima in the graph

The hydrogen-hydrogen interaction is 4.0 kJ/mol and the eclipsing interaction between is 6.0 kJ/mol. The least stable conformation has one eclipsed H-H interaction and two ${\text{H - CH}}_{\text{3}}$ interactions. The energy maxima can be calculated as:   

                            $$\begin{gathered} \text{Energymaxima = 2}\left(\text{6.0kJ/mol}\right)\text{ + 4.0kJ/mol} \\ \text{ = 12.0kJ/mol + 4.0kJ/mol} \\ \text{ = 16.0kJ/mol} \end{gathered}$$

The graph with relative energy maxima can be given as:

                                            Energy vs. the angle of rotation