Atom chlorine

Two significant changes have taken place with regard to transfer reactions of chlorine atoms since the review of Fettis and Knox [52] in 1964. The amount of quantitative data has almost doubled (see Table 5) 

Metathetical reactions of chlorine atoms transfer of hydrogen atoms 

Benson et al. [76] have used the thermal decomposition of ICl as a source of Cl atoms and studied the reaction 

H-abstraction reactions of chlorine atoms are often the basis of bond dissociation energy determinations, viz. 

For this pair of reactions, if the activation energies can be measured (usually in separate kinetic systems), it follows from thermochemistry that 

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Benzene can undergo addition reactions which successively saturate the three formal double bonds, e.g. up to 6 chlorine atoms can be added under radical reaction conditions whilst catalytic hydrogenation gives cyclohexane. 

The nitrochlorobenzenes are valuable dyestufTs intermediates. The presence of the nitro-groups makes the chlorine atom very reactive and easily replaceable. Treatment with ammonia or dilute alkalis substitutes an amino- or hydroxy-group for the chlorine atom and gives a series of nilroanilines and nilrophenols. 

Prepared by condensing p-chlorophenol with phlhalic anhydride in sulphuric acid solution in the presence of boric acid. The chlorine atom is replaced by hydroxyl during the condensation. It can also be prepared by oxidation of anthraquinone or 1-hydroxyanthraquinone by means of sulphuric acid in the presence of mercury(ll) sulphate and boric acid. 

Figure Bl.8.4. Two of the crystal structures first solved by W L Bragg. On the left is the stnicture of zincblende, ZnS. Each sulphur atom (large grey spheres) is surrounded by four zinc atoms (small black spheres) at the vertices of a regular tetrahedron, and each zinc atom is surrounded by four sulphur atoms. On the right is tire stnicture of sodium chloride. Each chlorine atom (grey spheres) is sunounded by six sodium atoms (black spheres) at the vertices of a regular octahedron, and each sodium atom is sunounded by six chlorine atoms.

This compound, which contains atoms arranged tetrahedrally around the boron atom, can readily be isolated from a mixture of dimethyl ether and boron trichloride. On occasions a chlorine atom, in spite of its high election affinity, will donate an electron pair, an example being found in the dimerisation of gaseous monomeric aluminium chloride to give the more stable Al2Clg in which each aluminium has a tetrahedral configuration ... 

The strongly electronegative (p. 49) chlorine atom becomes a chloride ion, the proton accepting the electron pair donated by the nitrogen atom. A similar reaction occurs when ammonia is passed into water, but to a much lesser extent as oxygen in water is a poorer donor of the electron pair ... 

Pure anhydrous aluminium chloride is a white solid at room temperature. It is composed of double molecules in which a chlorine atom attached to one aluminium atom donates a pair of electrons to the neighbouring aluminium atom thus giving each aluminium the electronic configuration of a noble gas. By doing so each aluminium takes up an approximately tetrahedral arrangement (p. 41). It is not surprising that electron pair donors are able to split the dimer to form adducts, and ether, for example, forms the adduct. 

In silicon tetrachloride, SiC, chlorine atoms can be replaced by methyl or other alkyl groups to give, for example, CHjSiClj and (CH3)2SiCl2. These two compounds are obtained when methyl... 

Silica gel is again obtained but silicon does not form the corresponding hexachlorosilicic acid since the small silicon atom is unable to coordinate six chlorine atoms. 

The replacement of the —OH group by a chlorine atom (reaction 9.4) is a very general reaction of phosphorus pentachloride. For example, if concentrated sulphuric acid is written as (H0)2S02 then its reaction with phosphorus pentachloride may be written ... 

Chlorine substitutes the hydrogen of methane giving successively the chlorides CH3CI, CH2CI2, CHCI3 and CCI4. It is to be noted that if a hydrocarbon is unsaturated, chlorine atoms will first add to the double or triple bond after which substitution may occur. 

Ironilll) chloride is a black, essentially covalent solid, in which each iron atom is surrounded octahedrally by six chlorine atoms. It is prepared by direct combination of iron with chlorine or by dehydration of the hydrated chloride, by one of the methods given on p.343). 

Golddll) chloride dissolves in hydrochloric acid to form tetra-chlorauric acid. HAUCI4. Here again, the gold(III) is 4-co-ordinate in the ion [AuCl4] . If alkali is added to this acid, successive replacement of chlorine atoms by hydroxyl groups occurs, forming finally the unstable tetrahydroxoaurate IlI) ion, [Au(OH)4] ... 

A set of rules determines how to set up a Z-matrix properly, Each line in the Z-matiix represents one atom of the molecule. In the first line, atom 1 is defined as Cl, which is a carbon atom and lies at the origin of the coordinate system. The second atom, C2, is at a distance of 1.5 A (second column) from atom 1 (third column) and should always be placed on one of the main axes (the x-axis in Figure 2-92). The third atom, the chlorine atom C13, has to lie in the xy-planc it is at a distanc e of 1.7 A from atom 1, and the angle a between the atoms 3-1-2 is 109 (fourth and fifth columns). The third type of internal coordinate, the torsion angle or dihedral r, is introduced in the fourth line of the Z-matiix in the sixth and seventh column. It is the angle between the planes which arc... 

In order to allow any multiple chlorination of the biphenyl skeleton, the user may define an atom list (eonsisting of hydrogen and chlorine atoms) and substitute all H-atoms by this list. One may click on the drop-down selection box behind the element icons, select the options Generics. .set the user-defined atom to A1 and quit by the OK button. As a result this atom selection is active for the subsequent drawing steps. After this atom list is drawn ten times as the ten substituents, its composition has to be defined by clicking the A, icon on the left-hand side of the structure editor and by selecting H and Cl in the periodic table (Figure 5-16). 

Figure 5-16. Structure editor of the CrossFire ComiTiander V6, showing the definition ofan atom list (consisting of hydrogen and chlorine atoms) for polychlorinated biphenyls.

Both precursors can be used as reactants in an aldol condensation. It has to be emphasized that the chlorine atom in 4 has to be considered as a representative for any electron-withdrawing group in particular, in the case presented here, it would best be taken as an OEt group. In order to verify this proposal, a reaction substructure search is initiated in the Chcmlnform reaction database of 1997. 

In the absence of catalysts, toluene when treated with chlorine (or bromine) at the boiling point, preferably with exposure to sunlight or other bright light source, undergoes halogenation in the side chain. The entrance of the first chlorine atom, for example, proceeds at a much faster rate than the entrance of the second chlorine atom so that in practice the major portion of the toluene is converted into benzyl chloride before appreciable chlorination of benzyl chloride occurs ... 

Dinitroaniline. This preparation is another illustration of the mobile character of the chlorine atom in 2 4-dinitro-l-chlorobenzene ... 

Formate is an excellent hydride source for the hydrogenolysis of aryl halides[682]. Ammonium or triethylammonium formate[683] and sodium formate are mostly used[684,685]. Dechlorination of the chloroarene 806 is carried out with ammonium formate using Pd charcoal as a catalyst[686]. By the treatment of 2,4,6-trichloroamline with formate, the chlorine atom at the /iiara-position is preferentially removed[687]. The dehalogenation of 2,4-diha-loestrogene is achieved with formic acid, KI, and ascorbic acid[688]. 

The amino group of 2-imino-3-phenyl-4-amino-5-carbethoxy-A4-thiazoline is very reactive and displaces the chlorine atom of various 2-chlorothiazoles (1577). 

Transfer of an electron from a sodium atom to a chlorine atom yields a sodium cation and a chloride anion both of which have a noble gas electron configuration... 

The boiling points of the chlorinated derivatives of methane increase with the num ber of chlorine atoms because of an increase m the induced dipole/mduced dipole attrac tive forces... 

Each chlorine atom formed m the initiation step has seven valence electrons and IS very reactive Once formed a chlorine atom abstracts a hydrogen atom from methane as shown m step 2 m Figure 4 21 Hydrogen chloride one of the isolated products from... 

Step 1 Dissociation of a chlorine molecule into two chlorine atoms... 

Chlorine molecule Two chlorine atoms (b) Cham propagation... 

Step 2 Hydrogen atom abstraction from methane by a chlorine atom... 

Chlorine atom Methane Hydrogen chloride Methyl radical... 

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