Iodides reactivity order

In fee absence of fee solvation typical of protic solvents, fee relative nucleophilicity of anions changes. Hard nucleophiles increase in reactivity more than do soft nucleophiles. As a result, fee relative reactivity order changes. In methanol, for example, fee relative reactivity order is N3 > 1 > CN > Br > CP, whereas in DMSO fee order becomes CN > N3 > CP > Br > P. In mefeanol, fee reactivity order is dominated by solvent effects, and fee more weakly solvated N3 and P ions are fee most reactive nucleophiles. The iodide ion is large and very polarizable. The anionic charge on fee azide ion is dispersed by delocalization. When fee effect of solvation is diminished in DMSO, other factors become more important. These include fee strength of fee bond being formed, which would account for fee reversed order of fee halides in fee two series. There is also evidence fiiat S( 2 transition states are better solvated in protic dipolar solvents than in protic solvents. 

As usual, the reactivity order with respect to halogen in C=C-X is I > Br > Q. The organic halide in the couplings with alkynylzinc halides is usnaily an iodide, though also activated vinylic bromides (e.g. BrCH=CHCOOC2H5) have been found to react smoothly. We... 

Electrochemical properties of samarium(ii) iodide are very sensitive to the nature of solvents. Reduction potential increases by replacing THE with a more polar solvent, such as DME or CH3CN. Addition of HMPA to a THE solution of samarium(ii) iodide leads to a substantial increase in the electron-donating nature of samarium(ii). The principal samarium(ii) species in a mixed solvent of THE and HMPA is an ionic cluster of [Sm(HMPA)4(THE)2] 2I in HMPA-THF (4 1) or [Sm(HMPA)6] 2I in HMPA-THE (>10 1). The reactivity order of the samarium(ii) complexes is [Sm(HMPA)6] 2I > [Sm(HMPA)4(THF)2] 2P > Sml2 in the reaction with 1-iodobutane. 

Cyclopentadienyl iodide (5-iodo-l,3-cyclopentadiene) reacts approximately 10 times as rapidly as cyclopentenyl iodide (3-iodocyclopentene) with tetrabutylammonium bromide under the same conditions (Breslow, R. Canary, J. W., J. Am. Chem. Soc., 1991, 113, 3950). Under solvolysis conditions (SnI), the reactivity order is reversed. Provide a rationalization based on the frontier orbitals of the system. What would you predict for the analogous 3- and 7-membered ring systems ... 

The reactivity order of the halides is I > Br > Cl F. Whereas magnesium and lithium react well with chlorides, bromides, and iodides, zinc is satisfactory... 

A notable feature in all these coupling protocols is that the coupling rates of iron-phosphorus systems, of the (salen)iron complex 5, the Fe(acac)3 catalyst, and catalyst 10 with respect to the alkyl halide are rather uncommonly bromide> iodide>chloride (entries 3, 4, 9, 13), whereas the reactivity order for iron-amine catalyst systems is iodide>bromide>chloride (entries 1, 5, 6). 

The relative catalytic activities of the Ni group metals in the reactions of perfluoroalkyl and polyfluoroalkyl iodides with amines to give enamines were compared, and the reactivity order Ni > Pd > Pt was found523. 

Aryl iodides. Aryl iodides can be prepared in fair to good yields from aromatic hydrocarbons by the action of iodine and a copper salt. The observed reactivity order of various copper salts is CuClj > CuFj > CuCl > CufOOCCHjlj. The reaction is considered to involve a two-step sequence ... 

Generally, the reaction rates of aryl halides follow the order iodides > bromides > chlorides > fluorides. This fact can be used for the selective substimtion in polyhalogenated systems. For instance, 2-bromo -chlorotoluene gives 76% of 5-chloro-2-methylphenol by treatment with sodium hydroxide at 200 °C. Nevertheless, polyhalogenated systems which contain fluorides have a variable behaviour depending on the reaction temperature. At lower temperatures preferential hydrolysis of the fluoride takes place and at >200 °C the usual reactivity order iodides > bromides > chlorides > fluorides is observed. For instance, l,2-dibromo-3,4,5,6-tetrafluorobenzene affords 2,3-dibromo-4,5,6-trifluorophenol in 87% yield by treatment with potassium hydroxide at 85 °C. Under the same conditions, 1,4-dibromo-2,3,5,6-tetrafluorobenzene produces a 78% yield of 2,5-dibromo-3,4,6-trifluorophenol. However, 4-fluorobromobenzene with NaOH at 200 °C gives 4-fluorophenol in 70-79% yield. ... 

Most group VIII metals will, to some extent, catalyze carbonylation. Early work utilized Ni and iodine as catalyst. Using metal iodides on silica as carbonylation catalysts at 175-230°C, —27 MPa, and a 2 hr residence time shows the reactivity order Ni > Co... 

Reduction of halides. The TiCl3 3THF Mg system reduces bromides and iodides almost quantitatively at 20°. The reactivity order is I>Br>Cl>F. Alkenes are by-products in the reaction of aliphatic alicyclic halides. The source of the hydrogen that replaces halogen is not knovirn, but may be THF. 

The comparative reactivity order for AnthT ys.. Anth with chlorides and bromides is contrary to what is expected on the basis of their respective reduction potentials (17). This rate ratio changes by an order of magnitude in going from chlorides to bromides to iodides. For the iodides the rates of the two reactions are comparable but this surprising similarity may be fortuitous and may not in fact mean a similarity in mechanisms. Further discussion of this point appears in a subsequent section. 

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