Configuration mercury

Owing to their s electron configuration mercury atoms are less reactive and are stable in many solvents such as alkanes and water under ambient conditions [27,146,147]. However, the solubility of atomic mercury is rather low (= 10" M). 

Mercuration. Mercury(II) salts react with alkyl-, alkenyl-, and arylboranes to yield organomercurials, which are usehil synthetic intermediates (263). For example, dialkyhnercury and alkyhnercury acetates can be prepared from primary trialkylboranes by treatment with mercury(II) chloride in the presence of sodium hydroxide or with mercury(II) acetate in tetrahydrofuran (3,264). Mercuration of 3 -alkylboranes is sluggish and requires prolonged heating. Alkenyl groups are transferred from boron to mercury with retention of configuration (243,265). 

Fig. 4. Configurations of mercury chlorine ceU anodes (a) blade type (b) mnner technology (c) rod type and (d) mesh type.

Mercury(I) compounds are diamagnetic, whereas the monatomic Hg+ ion would have a d s configuration and so be paramagnetic. 

With 6-alkenoic acids the intermediate radical partially cyclizes to a cyclopentyl-methyl radical in a 5-exo-trig cycHzation [139] (Eq. 6) [138 a, 140] (see also chap. 6). To prevent double bond migration with enoic acids the electrolyte has to be hindered to become alkaline by using a mercury cathode. Z-4-Enoic acids partially isomerize to -configurated products. Results from methyl and deuterium labelled carboxylic acids support an isomerization by way of a reversible ring closure to cyclopropyl-carbinyl radicals. The double bonds of Z-N-enoic acids with N > 5 fully retain their configuration [140]. 

Clearly, a study of the stereochemistry can distinguish between Se2 (back) on the one hand and Se2 (front) or Ssi on the other. Many such investigations have been made. In the overwhelming majority of second-order electrophilic substitutions, the result has been retention of configuration or some other indication of frontside attack, indicating an Se2 (front) or SeI mechanism. For example, when cis-l was treated with labeled mercuric chloride, the 2 produced was 100% cis. The bond between the mercury and the ring must have been broken (as well as the other Hg—C... 

The reaction has also been used to prepare 1,3-dilithiopropanes" and 1,1-dilithio-methylenecyclohexane" from the corresponding mercury compounds. In general, the equilibrium lies in the direction in which the more electropositive metal is bonded to that alkyl or aryl group that is the more stable carbanion (p. 228). The reaction proceeds with retention of configuration an Sgi mechanism is likely. Higher order cuprates (see Ref. 1277 in Chapter 10) have been produced by this reaction starting with a vinylic tin compound ... 

Tri-n-butyltin hydride can also be used for reductive demercuration.20 An alternative reagent for demercuration is sodium amalgam in a protic solvent. Here the evidence is that free radicals are not involved and the mercury is replaced with retention of configuration.21... 

The technique used to acquire the data in this paper was SNIFTIRS. A schematic diagram of the required apparatus is shown in Figure 5, and has been described in detail elsewhere. The FTIR spectrometer used was a vacuum bench Bruker IBM Model IR/98, modified so that the optical beam was brought upwards through the sample compartment and made to reflect from the bottom of the horizontal mercury surface. The methods used herein are adapted from a configuration that has been used by Bewick and co-workers (21) at Southampton. 

Zinc, cadmium and mercury are at the end of the transition series and have electron configurations ndw(n + l)s2 with filled d shells. They do not form any compound in which the d shell is other than full (unlike the metals Cu, Ag and Au of the preceding group) these metals therefore do not show the variable valence which is one of the characteristics of the transition metals. In this respect these metals are regarded as non-transition elements. They show, however, some resemblance to the d-metals for instance in their ability to form complexes (with NH3, amines, cyanide, halide ions, etc.). 

As mentioned earlier (see page 373), methylation of (+)-(i )-ethyl phenyl sulfoxide 136 with methyl iodide in the presence of mercury iodide affords the corresponding oxosulfonium salt (+)-(/ )-l 35 (172). That its demethylation by iodide anion yields sulfoxide 136 with the same configuration as that of the starting one indicates that 5-methylation of sulfoxides occurs with retention of configuration. 

To extend the levels of detection for mercury stiU lower, several workers, especially in this area of atomic absorption techniques, have chosen to collect the mercury on gold or other noble metal trapping systems prior to revaporizing the mercury into the measurement technique. Figure 7.14 shows the configuration of a specific system to concentrate mercury onto an amalgam preconcentrator prior to analysis. 

Mercury(II)systems For the halides and pseudohaUdes of the acceptor Hg2+ of the electron configuration AH and AHz have much the same value and so have also AHz and AHi. The two latter steps are much less exothermic than the first two. Generally this pattern is strikingly regular. In some cases where deviations have been reported, it seems plausible that these are not real but due to experimental error. This applies to the chloride system at / = 0.5 M where the very narrow range of existence of the third complex 37) makes the separation of AHz and AHi difficult and also to the iodide system where the low solubility of Hgl2 (zz. 10"4-i M Ref. 59)) detracts considerably from the accuracy of measurement. Especially the value of AH2 becomes rather uncertain. 

In this section, we will discuss organometallic derivatives of zinc, cadmium, mercury, and indium. The group IIB and IIIB metals have the d10 electronic configuration in the 2+ and 3+ oxidation states, respectively. Because of the filled d level, the 2+ or 3+ oxidation states are quite stable, and reactions of the organometallics usually do not involve changes in oxidation level. This property makes the reactivity patterns of these organometallics more similar to those of derivatives of the group IA and IIA metals than to those of derivatives of transition metals with vacancies in the d levels. The IIB metals, however, are... 

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