Activity series of the halogens

The activity series of the halogens. Reactivity decreases down Group 7A(17), so we can arrange the halogens into their own activity series ... 

Halogen reactivity decreases as one goes from top to bottom in the periodic table, because of the decreasing electronegativity. Therefore, a separate activity series for the halogens can be developed ... 

Buchmeiser and Nuyken [20], Weberskirch [21] and co-workers, examined the hydroformylation of 1-octene with a series of compounds of the formula [RhX(COD)(NHC)] (Fig. 9.1). The choice of halogen does not affect the reactivity, implying an active catalyst of the general formula [RhH(CO)3(NHC)]. Also, significant differences were observed in the initial TOF between catalysts (8,9) and (10,11) bearing iV- Pr and iV-Mes groups, respectively. Complex 11 exhibited a TOF of 1 480 h , whereas under identical conditions, 9 only turned over at a frequency of... 

This discussion of the energetics of the halogenate ions is in no way a digression. In the first place, when the reaction coordinate within a series is the same, a connection between driving force and rate can be expected. In the second place, it is important to realize that, if we are unable to understand the equilibrium stability in a basic way, we are hardly in position to deal effectively with the stabilities of the activated complexes. Increased concern with the stabilities of this important family of molecules, both at the experimental and theoretical levels, is justified. 

How does the activity of the halogens change in the series from fluorine to iodine How can this be explained ... 

Heinrikson et al. (161) have extended the study of the reaction at pH 5.5 to a series of halo acids, investigating the effect of chain length, d and l antipodes, and the position of the halogen substituent. All of the alkylated products showed enzymic activities of less than 0.5%. A summary of the rates of reaction of the various compounds with both His 12 and 119 and free histidine are shown in Table VII. All of the reagents react more rapidly with the protein than with free histidine. 

In the series of the IV-methyl-2,2,-bisimidazole (MBI) complexes R2SnX2 (MBI)130 (R = Me, Et, Bu, Ph X = Cl, Br) the butyl derivatives were the most active against KB (oral epidermoid human carcinoma) cell line. The nature of the halogen bound to the metal atom does not seem to have any influence on activity, except for the butyl complexes, for which the chloride is much more active (ID50 = 0.023 pgml-1), than bromide (ID50 = 0.170 pgml-1). 

The synthesis of modified cortical steroids has received particular interest since the report of greatly enhanced activity in the series of 9-halogen derivatives of hydrocortisone [23]. Further modifications have included the introduction of the C-l double bond [24] and the 2-methyl group [25]. The increased activity due to these latter changes has been attributed to protection of A-ring against inactivation via enzymatic reduction. [26] It seemed reasonable to suppose that a 6a-meth-yl group would be similarly effective. 

The NPD is a destructive detector that can be used in series only after non-destructive detectors (e.g. ECD). The NPD is sensitive to water that affects the condition of the thermoionic bead. The active element of the bead eventually will become depleted (especially when using halogenated solvents like dichloromethane, chloroform etc.) and requires replacement. 

Based on what you know about the electronegativity and electron affinity for the halogens, explain the organization of the halogen activity series. 

Describe how to use the activity series of metals and the activity series of halogens. 

Relate any periodic trends that you identify among the halogens to the activity series of halogens shown in Figure 10-10. 

A metal will not always replace another metal in a compound dissolved in water because metals differ in their reactivities. Reactivity is the ability to react with another substance. An activity series of some metals is shown in Figure 9.13. This series orders metals by reactivity with other metals. Single-replacement reactions are used to determine a metal s position on the list. The most active metals are at the top of the list. The least active metals are at the bottom. Similarly, the reactivity of each halogen has been determined and listed, as shown in Figure 9.13. 

Within the series of Pd" halogen complexes 14 (X=C1), 15 (X=Br) and 16 (X=I), the expected trends in the energies and geometry changes are again found the heavier the halogen, the smaller the activation energy and the earUer the transition state. The smallest barrier is calculated for iodide complex AE =... 

Muchowski and co-workers have described the synthesis and bronchodilator activity of a series of ring halogenated prostaglandins. Several of these compounds showed excellent activity in the Konzett assay (ys. histamine) on intravenous or aerosol administration (Table X). Phase I evaluation of the most potent member of the series, 9-deoxy-9p-fluoro-PGE2 (IX), however, revealed a cough liability which precluded further clinical investigation (126,130). 

The activity of the non-halogenated sulfonamide herbicide asulam (105 1965, Asulox , May Baker 1-10 kg-a.i. ha ) [196] was remarkable improved by replacing the 4-aminophenyl ring with a halogenated triazolopyrimidine moiety and/or by replacement the N-methoxycarbonyl group with a series of ortho-halogenated electron-deficient phenyl rings such as 2,6-difluoro-, 2,6-dichloro- or... 

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