Group II ions

Most of the metals react with water and, therefore, with any aqueous solution giving effectively M (Group D and M " (Group II) ions ... 

In any given period, the Group II ions are smaller and may then approach each other more closely. At the same time, twice as many electrons are present in the electron sea. The closer approach and the much greater electrostatic... 

Owing to the slight solubility of thallium(I) chloride, some of the thallium is also precipitated in Group IIIB (compare lead). It is often, however, precipitated with Group II ions. 

The lanthanide M2+ ions resemble the Group II ions, especially Ba2+. Thus the sulfates are insoluble whereas the hydroxides are soluble, and the Eu2+ ion can be readily separated from the other lanthanides by Zn reduction followed by the precipitation of other hydroxides by carbonate-free ammonia. The resemblance is also shown by the fact53 that the complexity constant of Eu2+ towards EDTA lies between those of Ca2+ and Sr2 +. ... 

There is a marked contraction in size on the formation of an ion, the percentage contraction decreasing as the percentage loss in electrons decreases (for example Na Na" involves loss of one of eleven electrons, Cs -+ Cs" the loss of one of fifty-five electrons). Some values for Group II and III elements are shown in Tables 2.2 and 2.3 respectively. 

As with the hydroxides, we find that whilst the carbonates of most metals are insoluble, those of alkali metals are soluble, so that they provide a good source of the carbonate ion COf in solution the alkali metal carbonates, except that of lithium, are stable to heat. Group II carbonates are generally insoluble in water and less stable to heat, losing carbon dioxide reversibly at high temperatures. 

C = C triple bonds are hydrated to yield carbonyl groups in the presence of mercury (II) ions (see pp. 52, 57) or by successive treatment with boranes and H2O2. The first procedure gives preferentially the most highly substituted ketone, the latter the complementary compound with high selectivity (T.W. Gibson, 1969). 

Smith, R. L. Popham, R. E. The Quantitative Resolution of a Mixture of Group II Metal Ions by Thermometric Titration with EDTA, /. Chem. Educ. 1983, 60, 1076-1077. 

When )3-scission can occur in the radical, further reactions compete with acid amide formation. Thus oxaziridine (112) with iron(II) ion and acid yields stabilization products of the isopropyl radical. If a-hydrogen is present in the Af-alkyl group, radical attack on this position in (113) occurs additionally according to the pattern of liquid phase decomposition. 

The system aluminum/water belongs to group II where represents the pitting potential and lies between -0.8 and -1.0 V according to the material and the medium [22,23,36,39,42]. Since alkali ions are necessary as opposite ions to the OH ions in alkalization, the resistance increases with a decrease in alkali ion concentration (see Fig. 2-11). In principle, however, active aluminum cannot be protected cathodically [see the explanation of Eq. (2-56)]. 

The importance of the o-hydroxyl moiety of the 4-benzyl-shielding group of R,R-BOX/o-HOBn-Cu(OTf)2 complex was indicated when enantioselectivities were compared between the following two reactions. Thus, the enantioselectivity observed in the reaction of O-benzylhydroxylamine with l-crotonoyl-3-phenyl-2-imi-dazolidinone catalyzed by this catalyst was 85% ee, while that observed in a similar reaction catalyzed by J ,J -BOX/Bn.Cu(OTf)2 having no hydroxyl moiety was much lower (71% ee). In these reactions, the same mode of chirality was induced (Scheme 7.46). We believe the free hydroxyl groups can weakly coordinate to the copper(II) ion to hinder the free rotation of the benzyl-shielding substituent across the C(4)-CH2 bond. This conformational lock would either make the coordination of acceptor molecules to the metallic center of catalyst easy or increase the efficiency of chiral shielding of the coordinated acceptor molecules. 

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