S 2 Dimers

In the crystal structure of pyrite, which is modelled on the periclase structure (fig. 5.1), Fe2+ ions occupy Mg24- positions and the mid-points of (S-S)2- dimeric anions are located at the O2- positions. Each Fe2+ ion is in octahedral coordination with one sulphur atom belonging to six different (S-S)2- dimers, and the... 

X4)2 (s-tetrazine dimer) electronic spectrum, 397tf... 

Optical properties of cyanines can be usefiil for both chiral substituents/environments and also third-order nonlinear optical properties in polymer films. Methine-chain substituted die arbo cyanines have been prepared from a chiral dialdehyde (S)-(+)-2-j -butylmalonaldehyde [127473-57-8] (79), where the chiral properties are introduced via the chiral j -butyl group on the central methine carbon of the pentamethine (die arbo cyanine) chromophore. For a nonchiral oxadicarbocyanine, the dimeric aggregate form of the dye shows circular dichroism when trapped in y-cyclodextrin (80). Attempts to prepare polymers with carbocyanine repeat units (linked by flexible chains) gave oligomers with only two or three repeat units (81). However, these materials... 

S mg), dimer (peak I) and monomer (peak 2), ovalbumin (S mg) (peak 3), and cytochrome c (3 mg) (peak 4) was loaded onto a Fractogel EMD BioSEC column (600 X 16 mm) with a bed height of 600 mm. PBS (pH 7.2) was used as the eluent at a flow rate of I ml/min the sample volume was O.S ml. (B) The same protein sample as in A was injected onto a column of identical dimensions packed with unmodified Fractogel HW 6S. Without the tentacle modification the base matrix displays only a poor resolution of the test mixture. 

Watanabe et al,25-5 52s applied AMS dimer (116) as a radical trap to examine the reactions of oxygen-centered radicals (e.g. r-butoxy, cumyloxy, benzoyloxy). AMS dimer (116) is an addition fragmentation chain transfer agent (see 6.2.3.4) and reacts as shown in Scheme 3,96. The reaction products are macromonomers and may potentially react further. The reactivity of oxygen centered radicals towards 116 appears to be similar to that of S.2 1 Cumyl radicals are formed as a byproduct of trapping and are said to decay mainly by combination and disproportionation. 

S.2.2.2. Dimers and Clusters with Nonbridging Ligands 8.2.2.2.I. Syntheses from Metal Vapors. 

The above-reported data lead to the conclusion that the HOMO in [Tc6(/j-Br)6Br6]Br2] 3- is the a i-MO composed mainly of 5s(5p,)- and 4dz2-AO s of technetium and having 2bonding character with respect to short M-M bonds. In other words, the EHT calculations [106,107,113] overestimate the interaction of <5 - and n -MO s of dimers in the horizontal directions and underestimate the participation of 5s- and 5pz-AO s in the formation of M-M bonds [15,142],... 

Diastereomerically pure (2W,5.V)-l,3-diaza-2-(2-methylphenyl)-3-phenyl-2-phosphabicyclo[3.3.0]octane (.S )-202] was formed in the thermal reaction of (S)-2-(anilinomethyl)pyrrolidines (197a) with o-TolP(NMe2)2 and isolated in 27% yield after recrystallization (Scheme 56) [87], Its cyclopalladation with palladium diacetate followed by anion metathesis gave dimer (5,5)-203 (Scheme 56) [87],... 

Scheme 9.2 Prior approaches to the C3-C3 linked dimers, (a) Hendrickson s oxidative dimerization approach to chimonanthine. (b) Scott s oxidative dimerization of tryptamines. (c) Overman s intramolecular Heck reaction, (d) Overman s asymetric alkylation...

Cycloadditions are in general an effective way of constructing cyclobutane rings. A wide variety of heterocyclic systems dimerize in this way. 1,3-Diacetylindole, for example, affords the head-to-tail dimer 242 on irradiation in ethanol.185 Ethyl 2-ethoxy-l,2-dihydroquinoline-l-carboxy-late is similarly converted in diethyl ether into the trans head-to-head dimer.186 Notable among many analogous photodimerizations are those reported in 1,4-dihydropyridines,187 in furo[3,2-b]pyridin-2(4//)-ones,188 in 8-methyl-s-triazolo[4,3-a]pyridine,189 and in 2H-2-benzazepine-1,3-diones.190 The [ 2 + 2] dimerization of amidopyrine is the first reported example of a photocycloaddition in a 4-pyrazolin-3-one.191... 

This indicates that in the process of vaporization 1 mole of liquid is converted into 2 moles of vapor. Therefore, we conclude that [Al(C2ff5)3]2 dimers are present in the liquid, but the vapor consists of monomeric Al(C2ff5)3 units. Examination of the data for [Al(Cff3)3]2 shows an entropy of vaporization of 112.61 mol 11<, which is greater than the value of 881 mol-1 K 1 predicted by Trouton s rule, but it is lower than twice the value. This value could be interpreted as corresponding to a liquid that is only partially dimerized being converted completely into monomer during vaporization. 

Polymerization and oligomerization reactions. l-FIalogenopropane-2-thiones give homopolycondensation,10 in different conditions l-chloropropane-2-thi-one11 forms a polymer or a cyclic trimer. a-Oxothioketones12 15 form dimers, by [4+2] unsymmetrical Diels Alder cycloaddition (Scheme 7). a,p-Unsatu-rated thioketones,16 Scheme 3 E = S, form dimers via head-to-head (R1 = Ph, R2 = Me) and head-to-tail (R1 = R2 = Ph), while selenoketones, E = Se, dimerize17 via head-to-head . 

The dithiophosphonic acid monoesters, RP(OR )(S)SH can be conveniently prepared by cleavage of dimeric, cyclic diphosphetane disulfides, [RP(S)S]2 with alcohols, silanols, or trialkylsilylalcohols180 and then can be converted into metal complexes M[SPR(OR )]2 without isolation.181 The substituted ferrocenyl anion, (N3C6H4CH20)(CpFeC5H4)PS2 has been prepared in two steps from P4Sio, ferrocene and hydroxymethylbenzotriazole (and its salt was used for the preparation of some nickel and rhodium complexes).182 Zwitter-ionic ferrocenylditiophosphonates,... 

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