DMSO solution

Obviously, to model these effects simultaneously becomes a very complex task. Hence, most calculation methods treat the effects which are not directly related to the molecular structure as constant. As an important consequence, prediction models are valid only for the system under investigation. A model for the prediction of the acidity constant pfQ in aqueous solutions cannot be applied to the prediction of pKj values in DMSO solutions. Nevertheless, relationships between different systems might also be quantified. Here, Kamlet s concept of solvatochro-mism, which allows the prediction of solvent-dependent properties with respect to both solute and solvent [1], comes to mind. 

Some results have been published on 2-alkylisothiazole-3- and -5-thiones (75CJC836, 80JCS(P 1)2693). As expected, the resonance of the carbon attached to the exocyclic sulfur atom is shifted downfield, to around 185 p.p.m. in the case of the 3-thiones and to over 190p.p.m. for the 5-thione. It is possible that CNMR chemical shifts could be used to investigate tautomerism in related compounds. Saccharin has carbon resonances at 161.0 (3), 127.9 (3a), 125.1 (4), 134.7 and 135.5 (5 and-6), 121.2 (7) and 139.5 (7a) p.p.m. in DMSO solution <82UP41700>. 

Meldrum s acid, pK 7.4, is exceptionally acidic in comparison to an acyclic analog such as dimethyl malonate, pK 15.9. For comparison, 5,5-dimethyl-1,3-cyclohexane-dione is only moderately more acidic than 2,4-pentanedione (11.2 versus 13.43). The pK values are those for DMSO solution. It is also found that the enhanced acidity of Meldrum s acid derivatives decreases as the ring size is increased. Analyze factors that could contribute to the enhanced acidity of Meldrum s acid. 

This reaction can also be applied to tertiary nitroalkanes lacking any additional functional group. The reactions with nitro compounds lacking additional anion-stabilizing groups are carried out in DMSO solution ... 

Ring-chain tautomerism of derivatives of 1,3,4-triazolidines 283 involves the equilibrium of three isomeric forms (Scheme 102) [90TL3927 96AHC(66)1, p. 33], In DMSO solution, the predominant form (about 70%)is 283c, the content of 283a and 283b varied between 13-25% and 5-17% respectively. 

Five possible isomers may coexist in the tautomeric equilibrium involving 2,6-diazidopurine 343 (Scheme 135). It was concluded (75UK1028) that diazide 343AA is the sole form in the solid state and in solutions in acetic and trifluoroacetic acids. In DMSO solution, two additional tautomers, 343AT and 343ATS were also observed. 

Wentrup s paper [98JCS(P2)2247] contains one of the very few contributions to the tautomerism of functionalized 1,3-diazepines. l,3-Dihydro-l,3-diazepin-2-ones (49a) exist as such and not as hydroxy tautomers 49b ( H and NMR in DMSO solution and IR in the solid state). 

Phenoxaphosphine ring-containing poly (1,3,4-oxa-diazoles) were synthesized by cyclodehydration of poly-hydrazides obtained from (BCPO) and aliphatic and aromatic dihydrazines [152]. All these polymers are soluble in formic acid, w-cresol and concentrated H2SO4. The polyhydrazides yield transparent and flexible films when cast from DMSO solution under reduced pressure at 80-100°C. The polyhydrazides exhibit reduced viscosities of 0.24-0.40 dl/g in DMAC. Phenoxaphosphine ring-containing oxadiazole polymers showed little degradation below 400°C. 

The best understood compounds are cis- and fra s-RuX2(DMSO)4 (X = Cl, Br). The fra s-isomers are thermodynamically less stable and isomerize in DMSO solution to the m-isomer, with first-order kinetics, probably via a dissociative mechanism. The reverse process, cis to trans, is catalysed by light. Syntheses for these and other DMSO complexes are shown in Figure 1.37 [108],... 

Three isomers of [Ru(NO)Cl (2equ)2] (2equ = 2-ethyl-8-quinolinate) have been isolated in the solid state they interconvert in DMSO solution above 100°C (NMR) [120],... 

There is some reason36 to believe that this noticeable change in the reactivity of AN in DMSO solution, is caused by the dipole-dipole interaction of the nitrile group of AN with the sulfinyl group of the DMSO molecule, resulting in an appreciable... 

Recent studies have found enhanced substituent solvation assisted resonance effects in dipolar non-hydrogen bonding solvents131. For several +R substituents acidities of phenols in DMSO are well correlated with their gas-phase acidities. The substituents include m- and p-SOMe, m- and p-S02Me, m-S02CF3 and m-N02. But there is very considerable enhancement of the effect of p-S02CF3, p-N02 and various other para-substituents in DMSO solution. 

The order is fairly similar to that observed for acidities in DMSO solution ... 

Kira and coworkers25 found that in deaerated DMSO solution of frans-stilbene both the solute cation and anion are produced and the anions are eliminated by aeration. Since they found26 that the absorption spectra of the anthracene cation and anion are quite similar, they suggested25 that the absorption spectrum observed by Hayon for anthracene solution in DMSO is a superposition of the spectra of the solute cation and anion. This observation casts a serious question on the yield of solvated electrons found by Hayon23. 

From the pulse radiolysis of DMSO solutions of naphthalene and the absorption of the naphthalene triplets (e = 2.26 x 104 M "1 cm 1) Hayon23 found that the yield of triplet excited states in irradiated DMSO is G = 0.57 and G = 0.36 for DMSO saturated with argon gas or N20 gas, respectively. 

Figure 20. Plot of the potential of zero charge, Egmo, vs. the electron work function, 4>, for metals in DMSO solutions, exhibiting the same general features as for aqueous solutions (Fig. 14).

The FT-IR spectroscopic measurements shown that in most cases the -COO or -0 groups formed a bridge between two Sn central atom, and polymerization occurred. The pqs approximations proved the formation of complexes with Oh, Tbp, and structures. H NMR measurements performed in DMSO solution have shown that the polymeric structure of the complexes does not persist in solution, and depolymerization occurs.. ... 

The pattern K j < K P < K° and X > X° > X is also clearly shown in the correlation of the proton nmr shifts of substituted phenols in DMSO solution. The o and p- substituent effects are best fitted by the a (A) parameters (cf. para set no. 24 of Table VI), whereas the m- substituent effects are best fitted by parameters. The following fitting parameters are... 

Kuhn s carbanion, the all-hydrocarbon anion tris(7//-dibenzo[c,g]-fluorenylidenemethyl)methanide ion [2 ] (Kuhn and Rewicki, 1967a,b), is a stabilized system with tt electrons widely spread over the sp hybridized carbon framework, and was isolated as the potassium salt. It also appears in DMSO solution by dissolving the parent hydrocarbon, resulting in a deep green colour. The pKg value of the precursor hydrocarbon [2]-H is 5.9 in aqueous HCl-DMSO (Kuhn and Rewicki, 1967a,b), and its enormous stability, as compared with cyclopentadiene [9]-H, pKa 18 in DMSO... 

The IR spectra (KBr disk) of the salts consist of absorptions of both the component cation, [T ], [24" ], [26 ], [28 ] or [40 ], and Kuhn s carbanion [2 ]. The ultraviolet-visible (UV-vis) spectra (DMSO solution) also agree with those of the component cation and anion superimposed, except that [26 2 ] undergoes partial coordination into the covalent form [26-2] in DMSO, as indicated by the presence of only =90% of the theoretical amount of [2 ] at the concentration of =10 m. 

The complete dissociation of the hydrocarbons [l 2 ], [28" 2 ] and [40" 2 ] in DMSO has been demonstrated by quantitative generation of both Kuhn s carbanion [2 ] and carbocations [1" ], [28" ] and [40" ] as determined by UV-vis spectra (Table 6 and Eig. 4). However, since carbocation [24 ] has no absorptions at a wavelength region longer than 220 nm in the UV spectrum, there remained an ambiguity that this cation might have decomposed in the DMSO solution. A clue to this problem could be obtained by determination of the electric conductivity of DMSO solutions of hydrocarbon salts (Table 7) (Okamoto et al., 1990). 

To overcome some of the problems associated with aqueous media, non-aqueous systems with cadmium salt and elemental sulfur dissolved in solvents such as DMSO, DMF, and ethylene glycol have been used, following the method of Baranski and Fawcett [48-50], The study of CdS electrodeposition on Hg and Pt electrodes in DMSO solutions using cyclic voltammetry (at stationary electrodes) and pulse polarography (at dropping Hg electrodes) provided evidence that during deposition sulfur is chemisorbed at these electrodes and that formation of at least a monolayer of metal sulfide is probable. Formation of the initial layer of CdS involved reaction of Cd(II) ions with the chemisorbed sulfur or with a pre-existing layer of metal sulfide. 

---