Chapter 26, Problem 26.69P

Interpretation Introduction

Interpretation:

Methyl acrylate and methyl methacrylate react with radical initiators (R•) as shown here. The difference in their reactivities in free radical polymerizations is dramatic. For example, methyl acrylate is less reactive with radicals than methyl methacrylate, but free radicals formed from methyl acrylate are more reactive than those formed from methyl methacrylate. In other words, C is more reactive than A, and B is more reactive than D. It is to be explained, the above observations.

Concept introduction:

The breaking of a covalent bond, whereby the electrons making up that bond are distributed equally to the atoms which are disconnected is known as the homolytic bond dissociation or homolysis. So in homolysis generally radicals are formed. In homolysis, a covalent bond is a breakdown equally and each atom acquires a single electron which is called a radical and a single barbed arrow () is used to represents the movement of a single electron in a homolysis process. In homolysis, the radicals from a breaking of the weakest bond of the molecule give the major products. The weakest bond possesses the smallest bond dissociation energy. The stability order for radicals is ${\text{methyl radical < 1}}^{\text{o}}{\text{radical < 2}}^{\text{o}}{\text{radical < allylic radical < 3}}^{\text{o}}\text{radical}\text{.}$ The more stable radical is always in its lowest energy state. Since radicals are electron-poor like carbocation, the electron-donating groups increase the stability of radicals.