... products or from a study of kinetics. The Formation of Radicals: Most of the important radical reactions proceed by a chain mechanism, the crucial step requires the generation of a radical from an appropriate pre - cursor. The molecules bond(s) need to be broken in such a way that each fragment keeps one electron. The energy required to break the bond(s) is supplied in one of the four following ways. (i) Photochemical cleavage- of compounds with weak bonds. Since a quantum of light with a wavelength of 300nm corresponds to ? 400 kJmol-1 . It is energetically feasible to cleave weak covalent bonds by irradiation with visible or UV light Well-known examples are halogens e.g.: Bromine (BDE = 193kJmol-1). Is a source of bromine atoms. (ii) Thermal cleavage- of weak bond. Compounds that contain relatively weak bonds, that is bonds with bond dissociation energies below 160kJmol-1 can undergo homolysis at a convenient rate at ...

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