Halogens Cl2, Br2, and

Examples of electrophilic reagents that normally add to carbon-carbon double bonds of alkenes to give saturated compounds include halogens (Cl2, Br2, and I2), hydrogen halides (HC1 and HBr), bypohalous acids (HOC1 and HOBr), water, and sulfuric acid ... 

Very interesting data were obtained for the reaction of polyfluorinated conjugated dienes with halogens (Cl2) Br2 and I2) at low temperature [79] ... 

The Halogens, Cl2, Br2, and I2 The action of halogens is dependent upon the conversion of electrically neutral halogen molecules into halogen ions by accepting electrons ... 

Non-metallic impurities, such as boron, free halogens (I2, Br2 and Cl2) and selenium in pharmaceutical substances usually contribute untoward reactions, skin manifestations and are found to be toxic to healthy tissues. 

Figure 4.34 compares the absorption spectra of the diatomic halogens, F2, Cl2, Br2, and I2. Cl2 is of particular recent interest in the troposphere in that levels up to 150 ppt have been observed in marine areas (Keene et al., 1993 Pszenny et al., 1993 Spicer et al., 1998). Table 4.30 summarizes the absorption cross sections of Cl2, Br2, and BrCl (DeMore et al., 1997 Marie et al., 1994 Hubinger and Nee, 1995). These diatomics all dissociated with a photodissociation quantum yield of 1 (Calvert and Pitts, 1966). 

Recent work on these systems includes Cl2, Br2, and several of the interhalogen molecules. The results can be summarized in terms of the potential curves in Figs. 3 and 4. The excited electronic states of the halogens are described in Hund s case c coupling, so that spin is not a good quantum number, and reasonably strong... 

Imidazole is known to be very reactive toward halogens, both Br2 and I2 giving the 2,4,5-trihalo derivatives in aqueous solution, whereas treatment with Cl2 appears to give uncharacterized ring-opened products (84MI2). Lambert and Jones, in a study of the kinetics of iodination of... 

Group names, melting point, density, and properties of compounds Groups 1,2, 17, and 18 are often identified with a group name. These names are shown in the table below. Several elements are found as diatomic molecules (H2, N2, 02, and the halogens F2, Cl2, Br2, and l2). Mnemonic devices to remember the diatomic elements are Br2l2N2Cl2H202F2 (pronounced Brinklehof and Have No Fear Of Ice Cold Beer. These molecules are attracted to one another using weak London dispersion forces. 

The halogens CI2, Br2, and I2 can also be oxidized to cationic species. Examples include the diatomic ions Bt2 and 12 (Cl2 has been characterized in low-pressure discharge tubes but is much less stable), and 12" dimerizes into 14 ... 

The kinetics of the gas-phase reactions of HBr with Cl2 and of HI with Cl2, Br2, and IC1 have been investigated by stopped-flow methods.27 The rate constants for the family of reactions can be rationalized if halogen and hydrogen halide molecules react to form a transition state in which the proton is near the centre of a triangle of three halogen atoms. In a study of the reaction ... 

The necessary vicinal dihalides are themselves readily available by addition of Br2 or Cl2 to alkenes. Thus, the overall halogenation/dehvdrohalogenation sequence makes it possible to go from an alkene to an alkyne. for example, diphenylethylene is converted into diphenylacetylene by reaction with Br2 and subsequent base treatment. 

A particularly common cr-substitution reaction in the laboratory is the halogenation of aldehydes and ketones at their a- positions by reaction with Cl2, Br2, or I2 in acidic solution. Bromine in acetic acid solvent is often used. 

Using E° values, predict what will happen if, in turn, each halogen beginning at chlorine is added to a 1 M solution of ions of the next lower halogen Cl2 to Br-, Br2 to I-. Which halogen is oxidized and which is reduced in each case ... 

Fig. 19 Variation of the intermolecular stretching force constant ka with nucleophilicity Nb for several series of halogen-bonded complexes B- XY, where B is one of a series of Lewis bases and XY is Cl2, Br2, BrCl, C1F or IC1. N% were assigned by use of Eq. 4 with the choice of ICi = 10.0, hence the perfect straight line for the B- -IC1 series. The lines for the other series are those obtained by least-squares fits to the ka values using the Mb determined from the B- IC1 series. Points for E P- -IC1, E N- -C1F and EEN- BrCl are anomalous and were excluded from the fits (see text for discussion)... 

The rules for predicting angular geometries of halogen-bonded complexes B- XY have recently received support from a wide ranging analysis of X-ray diffraction studies in the solid state by Laurence and co-workers [205]. This study not only confirms the validity of the rules in connection with complexes B- XY, where XY is Cl2, Br2, I2, IC1 and IBr, with many Lewis bases B but also reinforces the conclusion that halogen bonds Z- X - Y show a smaller propensity to be non-linear that do hydrogen bonds Z- H — X. 

A halogen molecule contains one nonpolar covalent single bond, as shown by its Lewis structure. As we descend the 7A family from F2 to I2, the size of a halogen atom increases and so the bond length increases. The strength of the X-X bond varies it increases from F2 to Cl2, then decreases from Cl2 to Br2 to I2. 

In Part I of this experiment, different metals will be added to solutions of different aqueous ions to determine whether a spontaneous redox reaction occurs. Also tested will be the colors of three halogens and their corresponding halide ion in mineral oil. Halogens such as Br2(aq), Cl2(aq) and I2(aq) dissolve in nonpolar solvents such as mineral oil to give a characteristic color. And finally in Part I, various combinations of these halogens and halides will be mixed and observations recorded. 

---