Stabilities of alkanes can be compared by converting these compounds to a common product and comparing the amount of the heat given off. One possiblitiy would be to measure the heat of combustion from converting alkenes to `xo_(2)` and `H_(2)O` . The heats of combustion are of large values and measuring small difference in these large numbers is difficult. Alkene of the lowest heat of combustion among isomeric alkenes is of the lowest energy and is most stable.
Th stability of alkenes is often compared by meansuring the ehat of hydrogenation `9` heat given off, `Delta H_(h)^(@)` during catalytic hydrogenation. The heat of hydrogenation is in smal number, which provides more accurate energy difference.
For a compound containing more than one double bond, `Delta_(h)^(@)` is the sum of heat of hydrogenation of individual double bonds. For non `-` conjugated diens, this additive relatioship is found to hold. For conjugated dienes, however, the measured value is slightly lower than expected. Cumulated dienes, which are even less stable than non `-` conjugated dienes.
The more stable is the alkene, lower is the heat of combustion and heat of hydrogenation. More highly substituted double bonds are usually more stable. In case of cyclokanes, compounds having higher angle strin are less stable.
If the heat of hydrogenation of cyclooctene is about `23 k cal mo^(-1)`, what would be the probable `DeltaH_(b)` or `1,3,5,7-`cyclooctatetraene ?

Options

A. 92
B. 23
C. 71
D. 101

Answer

D

Explanation

But it should be more than `92 kcal,` some more energy is required for resonance also. That is why energy is more than `92kcal.`