Free Radical Reaction

Definition and structure of carbon free radicals
When a bond is split, it produces atoms or groups with lone electrons, which are called free radicals. A free radical with a lone electron on a hydrogen atom is called a hydrogen radical. A free radical with a lone electron on a carbon atom is called a carbon radical. A hydrogen free radical and an alkyl free radical (carbon free radical) are produced when the C-H bond in an alkane is homolysis. Free radical carbon sp2 hybrid, three sp2 hybrid orbitals have a planar triangle structure, each sp2 hybrid orbital and other atomic orbitals by axial overlap to form a σ bond, the bonding orbital has a pair of opposite spin electrons. A p orbital is perpendicular to this plane, and the p orbital is occupied by a lone electron.
2. Bond dissociation energy and carbon radical stability
(1) bond dissociation energy
The atoms in a molecule are always doing tiny vibrations around their equilibrium positions, molecular vibrations are similar to the movement of a ball connected by a spring, at room temperature, when the molecules are in the ground state, the amplitude is small, the molecules absorb energy, and the amplitude increases. If enough energy is absorbed, the amplitude increases to a certain extent, the bond breaks, and the heat absorbed is the enthalpy (ΔH) of the bond dissociation reaction, and the bond energy, or bond-dissociation energy, is expressed in Ed.
(2) Stability of carbon free radicals
The stability of the radical refers to the stability of its parent compound, which is much more unstable than the parent compound, and less stable than the parent compound. From the above dissociation energy data of C-H bond, it can be seen that the dissociation energy of C-H bond in CH4 is the largest, and the first compound in the same series is often relatively special; The hydrogen dissociation energy of CH3CH3 and CH3CH2CH3 on primary carbon is slightly lower than that of CH4, and both of them form primary free radicals. The hydrogen on the secondary carbon atom in CH3CH2CH3 has lower dissociation energy and forms secondary free radicals. The hydrogen on the tertiary carbon atom in (CH3)3CH breaks, which has the lowest dissociation energy and forms the tertiary free radical. One of the products of these bond dissociation reactions is that they are all the same, so the difference in bond dissociation energy is a reflection of the different stability of the carbon radical. The lower the dissociation energy, the more stable the carbon radical. Therefore, the stability order of carbon radicals is
3°C·>2°C·>1°C·>H3C·
In alkanes, the C-C bond can also be dissociated.