91Ó°ÊÓ

The Bond Dissociation energy determines the bond strength. The stronger the bond, the more is the bond dissociation energy and vice-versa.

The bond dissociation energy is positive.

The difference in the energy of the products and the reactants is called the enthalpy change of the reaction. The enthalpy change determines the relative bond strength of the reactants and the products.

For endothermic reactions, the enthalpy change is positive. In comparison, for the exothermic reactions, the

enthalpy change is negative.

When the bonds break, the $∆\mathrm{H}°$is positive; when the new bonds are formed, the $∆\mathrm{H}°$ is negative.

The resonance stabilized radical formed upon the homolytic bond fission of the indicated C-H bond is shown hereunder.

Resonance structures of Propene

b. The half-headed curved arrows to inter-convert the two resonance structures are shown hereunder.

Half-headed arrows showing the interconversion of resonance structures of Propene

c. For the resonance hybrid, the electron density of the single radical electron is shown above the two bonds under the effect of resonance.

Resonance Hybrid structure