Entering group effect substitution reactions

Entering group effect platinum complexes substitution reactions, 494 EXAFS spectroscopy cadmium complexes, 929 copper(II) complexes, 720 zinc complexes, 929... 

The reactions of Ni(II) are slower than those of the other M(II) ions in this group, and this metal ion has been studied most extensively because the rates fall conveniently in the range of the stopped-flow technique. The substitution kinetic results on Ni(OHj)5 have been reviewed by Wilkins. Some representative results are given in Table 3.20. The first impression of these data is that there are significant entering group effects on the rate constant, so that the mechanism appears to be I,. However,... 

Entering Groups. Rates of reaction of [PtCl4], [PtCl3(OH2)], and [PtCl2(OH2)2] with ethene are all rather similar. Rates and activation parameters for the reaction of a variety of uncharged platinum(ii) complexes with cyanide have been reported. The complexes in question are [PtCl(N02)(NH3)2], [Pt(N02)2(NH3>2], [Pt(CN)a-(en)], and rra s -[Pt(CN)(N02)(NH3)2] cyanide substitution follows the usual rate law [equation (1) above]. The variation of the second-order term with solvent composition for the reaction of [PtCl2(bipy)] with thiourea in aqueous dioxan and in aqueous THE has been discussed in terms of solvent effects on the initial and transition states (see Chapter 5 of this Part). ... 

The 1,2,5-thiadiazoles were relatively inert in electrophilic substitution reactions (see also Section 4.02.1.4). The parent ring does not react with bromine, either under irradiation or in the presence of iron(III) salts, nor does it enter the Friedel-Crafts or nitration reactions. Electrophilic deuteration has been effected in low yield under drastic conditions (250 °C in trideuterophosphoric acid). If the thiadiazole ring bears an activating group, e.g. amino or methyl, electrophilic substitution can be achieved <68AHC(9)107, 70RCR923). 

Homologous Nitro Compounds.—When the nitration of the benzene homologues is effected by direct action of the acid, as in the case of benzene, the nitro group enters the ring. In the case of toluene it takes the para and ortho positions.. If the nitro group is substituted in the side chain it is introduced by the reactions characteristic of the aliphatic nitro compounds, i.e, by the action of silver nitrite upon a halide. 

---