Atoms Cl

Figure B2.3.17. REMPI spectra of the HCl and DCl products from the reaction of Cl atoms with (CH3)3CD [63], The mass 36 and 2 ion signals are plotted as a fiinction of the 2-photon wavenumber. Assigmnents of the...

The reaction of an atom with a diatomic molecule is the prototype of a chemical reaction. As the dynamics of a number of atom-diatom reactions are being understood in detail, attention is now being turned to the study of the dynamics of reactions involving larger molecules. The reaction of Cl atoms with small aliphatic hydrocarbons is an example of the type of polyatomic reactions which are now being studied [M, 72, 73]. 

This method is used more particularly for hydroxy-compounds which also contain other groups (such as Cl atoms, etc,) which might be affected by the sodium hydroxide used in the following method. 

A diagrammatic illustration of the effect of an isotope pattern on a mass spectrum. The two naturally occurring isotopes of chlorine combine with a methyl group to give methyl chloride. Statistically, because their abundance ratio is 3 1, three Cl isotope atoms combine for each Cl atom. Thus, the ratio of the molecular ion peaks at m/z 50, 52 found for methyl chloride in its mass spectrum will also be in the ratio of 3 1. If nothing had been known about the structure of this compound, the appearance in its mass spectrum of two peaks at m/z 50, 52 (two mass units apart) in a ratio of 3 1 would immediately identify the compound as containing chlorine. 

Examples are rare except for the S2 point group. This point group has only an S2 axis but, since S2 = i, it has only a centre of inversion, and the symbol generally used for this point group is C,. The isomer of the molecule ClFHC-CHFCl in which all pairs of identical FI, F or Cl atoms are trans to each other, shown in Figure 4.11(b), belongs to the C, point group. 

In this sequence the Cl also acts as a catalyst and two molecules are destroyed. It is estimated that before the Cl is finally removed from the atmosphere in 1—2 yr by precipitation, each Cl atom will have destroyed approximately 100,000 molecules (60). The estimated O -depletion potential of some common CFCs, hydrofluorocarbons, HFCs, and hydrochlorofluorocarbons, HCFCs, are presented in Table 10. The O -depletion potential is defined as the ratio of the emission rate of a compound required to produce a steady-state depletion of 1% to the amount of CFC-11 required to produce the 1% depletion. The halons, bromochlorofluorocarbons or bromofluorocarbons that are widely used in fire extinguishers, are also ozone-depleting compounds. Although halon emissions, and thus the atmospheric concentrations, are much lower than the most common CFCs, halons are of concern because they are from three to ten times more destmctive to O, than the CFCs. 

Cyclodienes. These are polychlorinated cycHc hydrocarbons with endomethylene-bridged stmctures, prepared by the Diels-Alder diene reaction. The development of these insecticides resulted from the discovery in 1945 of chlordane, the chlorinated adduct of hexachlorocyclopentadiene and cyclopentadiene (qv). The addition of two Cl atoms across the double bond of the ftve-membered ring forms the two isomers of chlordane [12789-03-6] or l,2,4,5,6,7,8,8-octachloro-2,3,3t ,4,7,7t -hexahydro-4,7-methano-lJT-indene, QL-trans (mp 106.5°C) and pt-tis (32) (mp 104.5°C). The p-isomerhas signiftcantiy greater insecticidal activity. Technical chlordane is an amber Hquid (bp 175°C/267 Pa, vp 1.3 mPa at 25°C) which is soluble in water to about 9 fig/L. It has rat LD qS of 335, 430 (oral) and 840, 690 (dermal) mg/kg. Technical chlordane contains about 60% of the isomers and 10—20% of heptachlor. It has been used extensively as a soil insecticide for termite control and as a household insecticide. 

Photochemistry. Vinyl chloride is subject to photodissociation. Photexcitation at 193 nm results in the elimination of HCl molecules and Cl atoms in an approximately 1.1 1 ratio (69). Both vinyUdene ( B2) [2143-69-3] and acetylene have been observed as photolysis products (70), as have H2 molecules (71) and H atoms [12385-13-6] (72). HCl and vinyUdene appear to be formed via a concerted 1,1 elimination from excited vinyl chloride (70). An adiabatic recoil mechanism seems likely for Cl atom elimination (73). As expected from the relative stabiUties of the 1- and 2-chlorovinyl radicals [50663-45-1 and 57095-76-8], H atoms are preferentially produced by detachment from the P carbon (72). Finally, a migration mechanism appears to play a significant role in H2 elimination (71). 

The total concentration or amount of chlorine-based oxidants is often expressed as available chorine or less frequendy as active chlorine. Available chlorine is the equivalent concentration or amount of Cl needed to make the oxidant according to equations 1—4. Active chlorine is the equivalent concentration or amount of Cl atoms that can accept two electrons. This is a convention, not a description of the reaction mechanism of the oxidant. Because Cl only accepts two electrons as does HOCl and monochloramines, it only has one active Cl atom according to the definition. Thus the active chlorine is always one-half of the available chlorine. The available chlorine is usually measured by iodomettic titration (7,8). The weight of available chlorine can also be calculated by equation 5. 

Demonstrations (a) Atom spring models (Fig. 4.2) on overhead projector to illustrate effect of structure on modulus, (b) Large models of Na atom and Cl atom, (c) Liquid nitrogen. 

Organic Carboxylic Acids — (RCOOH) are usually weak acids but can be very corrosive to skin. However, The substitution of Cl atoms on the carbon next to the carboxylic carbon produces a stronger acid. Thus, trichloroacetic acid is almost a strong acid whereas acetic acid is a weak one. 

It can be seen that all the Cl atoms in [AlCU] come from the AICI3. It was further shown that the same two species predominated when AI2I6 was dissolved in an excess of POCI3 ... 

Numerous tetrahedral halogeno complexes [T1" X4] (X = Cl, Br, I) have been prepared by reaction of quaternary ammonium or arsonium halides on TIX3 in nonaqueous solution, and octahedral complexes TI "X< ] (X = Cl, Br) are also well established. The binuclear complex Cs3[Tl2"Cl<)J is an important structural type which features two TlCls octahedra sharing a common face of 3 bridging Cl atoms (Fig. 7.9) the same binuclear complex structure is retained when Tl " is replaced by Ti ", V ", Cr " and Fe " and also in K3W2CIS and CssBiily, etc. 

Figure 13.12 Schematic representation of the structure of the complex anion LSbjCIiiO] " showing the two different coordination geometries about Sb and the unique quadruply bridging Cl atom.

It will be noted that the central I-l distance is close to that in I5+ and that the terminal 1-Cl distance is very similar to that in )3-lCl (p. 826). There are also strong secondary interactions so as to form infinite zig-zag chains via trans-Cl atoms of the octahedral SbCle" anions (1- Cl 294.1 pm, angle Cl-1 1 177.6°). 

SC2CI3 and its Br analogue are of unknown structure, as are reported La2X3 phases, though Y2CI3 and Y2Br3 have been shown to consist of parallel chains of Ye octahedra, the chains being linked by Cl atoms ... 

ScCl, made up of close-packed layers of Sc and Cl atoms in the sequence Cl-Sc-Sc-Cl has, like analogous Y and La materials with Cl and Br, since been shown to have been stabilised by interstitial H impurity. ... 

The reaetion of eone HCl and molybdenum aeetate at 0°C produees the diamagnetie red anion [Mo2Cl8]" (Fig. 23.11b) in whieh the 2 M0CI4 are in the eelipsed orientation relative to eaeh other and are held together solely by the Mo-Mo bond. At somewhat higher temperatures ( 50°C) the above reaetants also produee the [Mo2ClgH] ion whieh has the [Mj Clg] " strueture (Fig. 23.4) but with one of the bridging Cl atoms replaeed by a H atom. 

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