Low-temperature NMR study of conformational equilibration and reversible covalent association in dithioacetic acid

Rajab, Abdulrazak M.; Noe, Eric A.

doi:10.1021/ja00168a012

Cited by 10 publications

(3 citation statements)

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“…We have used dynamic NMR spectroscopy to study the possibility that esters, thiol acids, and thiol esters, with groups such as vinyl, phenyl, or hydrogen, which could not provide a pair of electrons to complete an “aromatic” sextet in the Z conformations, would have enhanced populations of the E isomers. The conformational equilibria for S -phenyl thioformate, phenyl formate, vinyl formate, thioacetic acid, and dithioacetic acid could be rationalized in terms of an effect of this type. The ethynyl group also could not support an aromatic sextet in the Z conformation, and an E − Z energy difference of only 1.7 kcal/mol was estimated for ethynyl formate by ab initio calculations.…”

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EandZConformations of Esters, Thiol Esters, and Amides

et al. 1998

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Populations and free-energy differences for the E and Z conformations of S-methyl, cyclopropyl, isopropyl, and cyclopentyl thioformate were determined by low-temperature 1H NMR spectroscopy, and free-energy barriers of 10.63 and 11.84 kcal/mol were obtained for interconversion of E and Z conformations of S-methyl thioformate at −52.4 °C. Populations and free-energy differences were also determined at room temperature by using 13C NMR for a series of N-substituted formamides and N-cyclopropylacetamide in 1% solutions in CD2Cl2/CH2Cl2. In both sets of compounds, electron-withdrawing groups attached to sulfur or nitrogen appear to favor the E conformations. The electronegativities of the groups are taken to increase in the order methyl < vinyl ∼ phenyl ∼ cyclopropyl < hydrogen < ethynyl. Data from the literature are discussed in these terms, including the E−Z energy differences for formic acid and its ethynyl, vinyl, and methyl esters.

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EandZConformations of Esters, Thiol Esters, and Amides

et al. 1998

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“…The chemistry of monothioacetic acid, which is much more acidic (p K a = 3.3) than the oxygen homologue acetic acid (p K a = 4.76), is extensively reviewed in the literature. , …”

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confidence: 99%

From Thioxo Cluster to Dithio Cluster: Exploring the Chemistry of Polynuclear Zirconium Complexes with S,O and S,S Ligands

et al. 2010

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Three different zirconium thio and oxothio clusters, characterized by different coordination modes of dithioacetate and/or monothioacetate ligands, were obtained by the reaction of monothioacetic acid with zirconium n-butoxide, Zr(OnBu)4, in different experimental conditions. In particular, we isolated the three polynuclear Zr3(μ3-SSSCCH3)2(SSCCH3)6·2nBuOH (Zr3), Zr4(μ3-O)2(μ−η1-SOCCH3)2(SOCCH3)8(OnBu)2 (Zr4), and Zr6(μ3-O)5(μ-SOCCH3)2(μ-OOCCH3)(SOCCH3)11(nBuOH) (Zr6) derivatives, presenting some peculiar characteristics. Zr6 has an unusual star-shaped structure. Only sulfur-based ligands, viz., chelating dithioacetate monoanions and an unusual ethane-1,1,1-trithiolate group μ3 coordinating the Zr ions, were observed in the case of Zr3. 1D and 2D NMR analyses confirmed the presence of differently coordinated ligands. Raman spectroscopy was further used to characterize the new polynuclear complexes. Time-resolved extended X-ray absorption fine structure measurements, devoted to unraveling the cluster formation mechanisms, evidenced a fast coordination of sulfur ligands and subsequent relatively rapid rearrangements.

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“…Traces of tetramethylhexathiaadamantane were also identified. Later on, the two trimers were isolated and characterized by their 13 C-NMR spectra [4], In a 'H-and 13 C-NMR study of the conformational equilibrium of dithioacetic acid, the appearance of weak extra signals in the expected region was observed and the possible formation of the same trimers was mentioned [5]. We tried to complement the characterization of these trimers by alkylation of the thiol functions in basic medium, as it was done for the trimers of the dithioformic acid [6].…”

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confidence: 99%