Why the ΔνCH blue shift is larger in chloral than in dichloroacetyl chloride dimers?

Raman spectra of the Cl₃CCHO/CCl₄ and Cl₃CCHO/C₆D₁₂ binary systems were recorded as a function of the mole fraction. Features originating from self‐aggregates of chloral (trichloroethanal, trichloroacetaldehyde—TCAA) molecules were detected in different spectral regions. The most pronounced changes were observed in the vicinity of the ν(CO) and ν(C H) stretching vibration bands. Using two‐dimensional correlation spectroscopy (2D‐COS), evolving‐factor analysis (EFA) and multivariate curve resolution (MCR), dimer bands were identified, and their positions were determined. The ν(C H) stretching vibration band in dimers was blue‐shifted by nearly 18 cm⁻¹, whereas the ν(CO) dimer band was red‐shifted by more than 5 cm⁻¹. For these bands, the observed shifts were accompanied by an almost twofold change in the bandwidth, from approximately 19 and 6 cm⁻¹ for dilute solutions (x = 0.05) to 36.6 and 11.5 cm⁻¹, respectively, in pure TCAA. The formation of dimers was confirmed by multivariate analysis of the Raman spectra of chloral recorded as a function of temperature. Analogous analysis of dichloroacetyl chloride (DCAC) spectra gave an 8.9 cm⁻¹ blue shift for the ν(C H) vibration band and − 5.5/− 10.1 cm⁻¹ shifts for the ν(CO) stretching vibrations of the two conformers present. To facilitate the interpretation of experimental findings, the optimized geometries and vibrational wavenumbers of the Cl₃CCHO/HCl₂CCClO molecules and (Cl₃CCHO)₂/(HCl₂CCClO)₂ dimers were calculated at the B3LYP/6‐311 + + G(3df,3pd) level. Copyright © 2010 John Wiley & Sons, Ltd.     

Chemoselective multicomponent one-pot assembly of purine precursors in water

The recent development of a sequential, high-yielding route to activated pyrimidine nucleotides, under conditions thought to be prebiotic, is an encouraging step toward the greater goal of a plausible prebiotic pathway to RNA and the potential for an RNA world. However, this synthesis has led to a disparity in the methodology available for stepwise construction of the canonical pyrimidine and purine nucleotides. To address this problem, and further explore prebiotically accessible chemical systems, we have developed a high-yielding, aqueous, one-pot, multicomponent reaction that tethers masked-sugar moieties to prebiotically plausible purine precursors. A pH-dependent three-component reaction system has been discovered that utilizes key nucleotide synthons 2-aminooxazole and 5-aminoimidazoles, which allows the first divergent purine/pyrimidine synthesis to be proposed. Due to regiospecific aminoimidazole tethering, the pathway allows N9 purination only, thus suggesting the first prebiotically plausible mechanism for regiospecific N9 purination.     

Electron transfer reduction of carboxylic acids using SmI2-H2O-Et3N

The first general method for efficient electron transfer reduction of carboxylic acids has been developed. The protocol using SmI(2)-H(2)O-Et(3)N allows for reduction of a variety of carboxylic acids in excellent yields and provides an attractive alternative to processes mediated by reactive alkali metals, lithium aluminum hydride, and boron hydrides. Of broader significance, the method allows acyl radical equivalents to be generated from carboxylic acids under mild reaction conditions.     

Quantitative determination of prednisone in tablets by infrared attenuated total reflection and Raman spectroscopy

The quantification of prednisone in tablets was performed using partial least squares (PLS) models based on FTIR-attenuated total reflection (ATR) and FT-Raman spectra. To compare the predictive ability of these models, the relative standard error of prediction (RSEP) values were calculated. In the case of prednisone determination from the FT-Raman data, RSEP values of 3.1 and 3.2% for the calibration and validation data sets were obtained. For FTIR-ATR models, which were constructed using five spectra for each sample, these errors amounted to 2.6 and 2.9%, respectively. Four commercial products containing 1, 5, 10, and 20 mg prednisone/tablet were quantified. Concentrations derived from the elaborated models correlated strongly with the results of reference analyses and with the declared values (in parentheses). The analyses gave recoveries of 100.0-101.6% (100.1-103.0%) and 98.1-103.2% (100.4-102.9%) for FTIR-ATR and FT-Raman data, respectively. A successful quantification of prednisolone in tablets containing 5 mg active ingredient/tablet was also performed using the PLS model, which was based on FTIR-ATR spectra, with a recovery of 99.8 (98.8%). Both reported spectroscopic techniques can be used as fast and convenient alternatives to the standard pharmacopeial methods of prednisone and prednisolone quantification in solid dosage forms. However, in the case of FTIR-ATR spectroscopy, it is necessary to repeat measurements several times to obtain sufficiently low quantification errors.     

Electrical anharmonicity and vibronic couplings contributions to optical nonlinearity of N-benzyl-2-methyl-4-nitroaniline crystal studied by FT-IR, polarized FT-NIR, resonance Raman and UV-vis spectroscopy

FT-IR and Raman spectra of the orthorhombic and monoclinic N-benzyl-2-methyl-4-nitroaniline (BNA) single crystals, powders, and BNA solutions were measured in the 15-4000 cm(-1) range, and complete assignments of bands to normal vibrations are proposed. The assignments have been reinforced by density functional theory (DFT) calculations. Polarized FT-NIR spectra of the orthorhombic (010) BNA plate were measured for the overtones and combinations analysis and for the mechanical and electrical anharmonicity estimation. Resonance Raman spectra of the orthorhombic BNA polymorph together with the resonance excitation profiles of fundamental and lattice vibrations, compared with the band maxima in the measured UV-vis-NIR spectra of BNA, have revealed vibronic couplings with intramolecular and intermolecular charge transfers. The role of anharmonicity, vibronic couplings and intermolecular hydrogen bonds as well as of the N-benzyl substituent are discussed and the origin of second harmonic generation in the orthorhombic BNA crystal is proposed.     

Thermal analysis, phase transitions and molecular reorientations in [Sr(OS(CH3)2)6](ClO4)2

Thermal analysis (TG/DTG/QMS), performed for [Sr(OS(CH₃)₂)₆](ClO₄)₂ in a flow of argon and in temperature range of 295–585 K, indicated that the compound is completely stable up to ca. 363 K, and next starts to decompose slowly, and in the temperature at ca. 492 K looses four (CH₃)₂SO molecules per one formula unit. During further heating [Sr(DMSO)₂](ClO₄)₂ melts and simultaneously decomposes with explosion. Differential scanning calorimetry (DSC) measurements performed in the temperature range of 93–370 K for [Sr(DMSO)₆](ClO₄)₂ revealed existence of the following phase transitions: glass ? crystal phase Cr5 at T _g  ≈ 164 K (235 K), phase Cr5 → phase Cr4 at $ T_{\text{c6}}^{\text{h}} $  ≈ 241 K, phase Cr4 → phase Cr3 at $ T_{\text{c5}}^{\text{h}} $  ≈ 255 K, phase Cr3 → phase Cr2 at $ T_{\text{c4}}^{\text{h}} $  ≈ 277 K, phase Cr2 ? phase Cr1 at $ T_{\text{c3}}^{\text{h}} $  ≈ 322 K and $ T_{\text{c3}}^{\text{c}} $  ≈ 314 K, phase Cr1 ? phase Rot2 at $ T_{\text{c2}}^{\text{h}} $  ≈ 327 K and $ T_{\text{c2}}^{\text{c}} $  ≈ 321 K and phase Rot2 ? phase Rot1 at $ T_{\text{c1}}^{\text{h}} $  ≈ 358 K and $ T_{\text{c1}}^{\text{c}} $  ≈ 347 K. Entropy changes values of the phase transitions at $ T_{\text{c1}}^{\text{h}} $ and $ T_{\text{c2}}^{\text{h}} $ (?S ≈ 79 and 24 J mol^?1 K^?1, respectively) indicated that phases Rot1 and Rot2 are substantially orientationally disordered. The solid phases (Cr1–Cr5) are more or less ordered phases (?S ≈ 7, 10, 4 and 3 J mol^?1 K^?1, respectively). Phase transitions in [Sr(DMSO)₆](ClO₄)₂ were also examined by Fourier transform middle infrared spectroscopy (FT-MIR). The characteristic changes in the FT-MIR absorption spectra of the low- and high-temperature phases observed at the phase transition temperatures discovered by DSC allowed us to relate these phase transitions to the changes of the reorientational motions of DMSO ligands and/or to the crystal structure changes.     

On the Role of Pre‐ and Post‐Electron‐Transfer Steps in the SmI2/Amine/H2O‐Mediated Reduction of Esters: New Mechanistic Insights and Kinetic Studies

The mechanism of the SmI₂‐mediated reduction of unactivated esters has been studied using a combination of kinetic, radical clocks and reactivity experiments. The kinetic data indicate that all reaction components (SmI₂, amine, H₂O) are involved in the rate equation and that electron transfer is facilitated by Brønsted base assisted deprotonation of water in the transition state. The use of validated cyclopropyl‐containing radical clocks demonstrates that the reaction occurs via fast, reversible first electron transfer, and that the electron transfer from simple Sm(II) complexes to aliphatic esters is rapid. Notably, the mechanistic details presented herein indicate that complexation between SmI₂, H₂O and amines affords a new class of structurally diverse, thermodynamically powerful reductants for efficient electron transfer to carboxylic acid derivatives as an attractive alternative to the classical hydride‐mediated reductions and as a source of acyl‐radical equivalents for C?C bond forming processes.     

Transition‐Metal‐Free Activation of Amides by N−C Bond Cleavage

The amide bond N?C activation represents a powerful strategy in organic synthesis to functionalize the historically inert amide linkage. This personal account highlights recent remarkable advances in transition‐metal‐free activation of amides by N?C bond cleavage, focusing on both (1) mechanistic aspects of ground‐state‐destabilization of the amide bond enabling formation of tetrahedral intermediates directly from amides with unprecedented selectivity, and (2) synthetic utility of the developed transformations. Direct nucleophilic addition to amides enables a myriad of powerful methods for the formation of C?C, C?N, C?O and C?S bonds, providing a straightforward and more synthetically useful alternative to acyl‐metals.     

Molecular dynamics of poly(ethylene 2,6-naphthalate)-polycarbonate composite by nuclear magnetic resonance

The aim of the work was to examine molecular dynamics of a series of poly(ethylene 2,6-naphthalate)-polycarbonate blends with changing weight ratio of copolymers by off-resonance nuclear magnetic resonance technique. It was shown that this technique provides information about the correlation times of the internal motions. The spectral density function amplitudes were estimated on the basis of the dispersion of the spin-lattice relaxation time off-resonanceT _lp^off. The measurements were performed for two series of blends which had been injection moulded with and without compatibilizer. The new polymer materials were also characterized using differential scanning calorimetry. Samples obtained after injection moulding and annealing became amorphous, which indicates that a reaction of transesterification process between the two polymers occurred.