Lewis structure free radicals

For such odd electron species (sometimes called free radicals) it is impossible to write Lewis structures in which each atom obeys the octet rule. In the NO molecule, the unpaired electron is put on the nitrogen atom, giving both atoms a formal charge of zero ... 

For each molecule, ion, or free radical that has only localized electrons, it is possible to draw an electronic formula, called a Lewis structure, that shows the location of these electrons. Only the valence electrons are shown. Valence electrons may be found in covalent bonds connecting two atoms or they may be unshared. The student must be able to draw these structures correctly, since the position of electrons changes in the course of a reaction, and it is necessary to know where the electrons are initially before one can follow where they are going. To this end, the following rules operate ... 

During the long Antarctic night, appreciable amounts of molecular chlorine, Cl, and hypochlorous acid, HOCl, accumulate within the polar vortex. When the sun returns during the spring (in September in Antarctica), ultraviolet radiation decomposes the accumulated molecular chlorine and hypochlorous acid to produce atomic chlorine. Cl. Atomic chlorine is a free radical. Free radicals are atoms or molecules that contain an unpaired or free electron. The Lewis structures of free radicals contain an odd number of electrons. The unpaired electron in free radicals makes them very reactive. The free radical Cl produced from the decomposition of CI2 and HOCl catalyzes the destruction of ozone as represented by the reaction ... 

The splitting of a Cl2 molecule is an initiation step that produces two highly reactive chlorine atoms. A chlorine atom is an example of a reactive intermediate, a short-lived species that is never present in high concentration because it reacts as quickly as it is formed. Each Cl- atom has an odd number of valence electrons (seven), one of which is unpaired. The unpaired electron is called the odd electron or the radical electron. Species with unpaired electrons are called radicals or free radicals. Radicals are electron-deficient because they lack an octet. The odd electron readily combines with an electron in another atom to complete an octet and form a bond. Figure 4-1 shows the Lewis structures of some free radicals. Radicals are often represented by a structure with a single dot representing the unpaired odd electron. 

Draw Lewis structures for the following free radicals. 

Isobutylene undergoes cationic polymerization in the presence of strong Lewis acids like AICI3 but it is not polymerized by free radicals or anionic initiators. Acrylonitrile, on the other hand, is polymerized commercially by free radical means and can also be polymerized by anionic im tiators like potassium amide but does not respond to cationic initiators. Account for the difference in behavior of isobutylene and acrylonitrile in terms of monomer structure. 

A stepwise process is used to convert a molecular formula into a Lewis structure, a two-dimensional representation of a molecule (or ion) that shows the relative placement of atoms and distribution of valence electrons among bonding and lone pairs. When two or more Lewis structures can be drawn for the same relative placement of atoms, the actual structure is a hybrid of those resonance forms. Formal charges are often useful for determining the most important contributor to the hybrid. Electron-deficient molecules (central Be or B) and odd-electron species (free radicals) have less than an octet around the central atom but often attain an octet in reactions. In a molecule (or ion) with a central atom from Period 3 or higher, the atom can hold more than eight electrons by using d orbitals to expand its valence shell. 

We have seen in the last chapter that electrons have a spin angular momentum corresponding to the quantum numbers -f i and In most molecules the electron spins are paired, but some molecules contain an odd number of electrons there is therefore at least one unpaired electron spin. An example of an ordinary molecule with an unpaired electron is nitric oxide (NO), which has an odd number (15) of electrons. Of particular interest are the free radicals, such as the methyl radical (CH3). This radical is produced if a hydrogen atom is abstracted from a methane (CH4) molecule, and its Lewis structure is... 

The unstable and highly reactive OH molecule is a free radical, a substance with one or more unpaired electrons, as seen in the Lewis structure -O — H. The OH molecule is also called the hydrox) l radical, and the presence of the unpaired electron is often emphasized by writing the species with a single dot, OH. In cells and tissues, hydroxyl radicals can attack biomolecules to produce new free radicals, which in turn attack yet other biomolecules. Thus, the formation of a single hydroxyl radical via Equation 2131 can initiate a large number of chemical reactions that are ultimately able to disrupt the normal operations of cells. 

Table 5.9 lists the structures of polychloroprenes that form by free-radical polymerization at different temperatures. Chloroprene polymerizes by cationic polymerization with the aid of Lewis acids in chlorinated solvents. When aluminum chloride is used in a mixture of ethyl chloride-methylene chloride solvent mixture at -80 °C, the polymer has 50% 1,4 units. If it is polymerized with boron trifluoride, the product consists of 50-70% 1,4-adducts. A veiy high trans-1,4-poly(2-chloro-1,3-butadiene) forms by X-ray radiation polymerization of large crystals of... 

Draw Lewis structures for the following free radicals, (a) The n-propyl radical, CH3—CH2—CH2 (c) The isopropyl radical... 

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