Question

There is no ring strain in cyclohexane, but cyclobutane has an angle strin of $9^{\circ }{44}^{\prime }.$ If $\Delta H_c^{\circ }$ of cyclohexane per $\left(C{H}_2\right)$ group is 660 kJ $mo{l}^{-1}$ and $\Delta H_c^{\circ }$ of cyclobutane is 2744 kJ $mo{l}^{-1}$, what is the ring strain in kJ $mo{l}^{-1}$ of cyclobutane ?

• A. - 104
• B. 104
• C. - 2084
• D. 2084

Answer 1

Answer: (B)

104

The $\Delta H_c^{\circ }$ value of cyclobutane is given. From this if we substract the $\Delta H_c^{\circ }$ value of cyclobutane calculated when there is no angle strain, we will get the value of ring strain of cyclobutane.
The $\Delta H_c^{\circ }$ value of cyclobutane when there is no ring strain can be calculated from $\Delta H_c^{\circ }$ value of cyclohexane per $C{H}_2$ group.
Ring strain = ($\Delta H_c^{\circ }$ of cyclobutane - $4\times \Delta H_c^{\circ }$ of per $\left(C{H}_2\right)$ group of cyclohexane) = 2744 - ($4\times 660$) = 104 kJ $mo{l}^{-1}$