Question

Heat of hydrogenation of ethene and benzene are $x_1$ and $x_2$. What will be the correct expression for resonance energy of Benzene?

• A. $x_1-x_2$
• B. $x_1+x_2$
• C. $3x_1-x_2$
• D. $x_1-3x_2$

Answer 1

The correct option is C $3x_1-x_2$

Hydrogenation of ethene,
$C{H}_2=C{H}_2+H_2\to C{H}_3-C{H}_3$
$\Delta H=x_1$
Theoretically, benzene has structure of 3 ethene in closed ring, so theoretical hydrogenation energy of benzene should be $3x_1$
Calculated hydrogenation energy of Benzene $=x_2$
So, Resonance energy $=[3x_1-x_2]$