We have developed a gold affinity index and hydrogen bonding basicity index for counterions and have used these indexes to forecast their reactivity in cationic gold catalysis.
This review deals with conformational analysis in small organic molecules, and describes the stereoelectronic interactions responsible for conformational stability. Conformational analysis is usually ...performed using NMR spectroscopy through measurement of coupling constants at room or low temperature in different solvents to determine the populations of conformers in solution. Quantum mechanical calculations are used to address the interactions responsible for conformer stability. The conformational analysis of a large number of small molecules is described, using coupling constant measurements in different solvents and at low temperature, as well as recent applications of through-space and through-hydrogen bond coupling constants JFH as tools for the conformational analysis of fluorinated molecules. Besides NMR parameters, stereoelectronic interactions such as conjugative, hyperconjugative, steric and intramolecular hydrogen bond interactions involved in conformational preferences are discussed.
This study investigated the effect of AgNPs and AgNO3, at concentrations equivalent, on the production of primary and secondary metabolites on transgenic soybean plants through an NMR-based ...metabolomics. The plants were cultivated in a germination chamber following three different treatments: T0 (addition of water), T1 (addition of AgNPs), and T2 (addition of AgNO3). Physiological characteristics, anatomical analyses through microscopic structures, and metabolic profile studies were carried out to establish the effect of abiotic stress on these parameters in soybean plants. Analysis of the 1H NMR spectra revealed the presence of amino acids, organic acids, sugars, and polyphenols. The metabolic profiles of plants with AgNP and AgNO3 were qualitatively similar to the metabolic profile of the control group, suggesting that the application of silver does not affect secondary metabolites. From the PCA, it was possible to differentiate the three treatments applied, mainly based on the content of fatty acids, pinitol, choline, and betaine.
The energy released when tetradecyltrimethylammonium bromide (C14TAB) is combined with different derivatives of chlorobenzoates in an isothermal titration calorimeter (ITC) allows a direct evaluation ...of the spontaneity of the threading of the aromatic anions into the micellar palisade. The comparison between the enthalpimetric curves with the ones for viscosity of the solutions, hydrodynamic radii of the aggregates (dynamic light scattering experiments), and the fraction of aromatic anions incorporated (diffusion-ordered spectroscopy experiments) allows the establishment of the variations of enthalpy with formation, growth, and decrease of the wormlike micelles (WLMs). The formation of WLMs with C14TAB is very favored (very exothermic) for titrations of chlorobenzoate derivatives which present the chlorine atom in positions 3 or 4 of the aromatic ring. However, the aggregation is highly unfavorable if chlorine is at position 2 of chlorobenzoate. According to the results, the high potential of the ITC to determine critical concentrations and the energies associated with the aggregation of a cationic surfactant and aromatic anions for the formation of WLMs was demonstrated.
Unusual 1 J CH values for an oxocane derivative were recently reported, highlighting the unexpected long-range Perlin effect for the 1 J CH. According to our theoretical and experimental results ...listed in this paper, the previous published data cannot be supported. Moreover, when comparing the previously studied oxocane derivative with analogous molecules, we realized that the difference between J-couplings actually comes from the increase in the 1 J C–Hax instead of decreasing of 1 J C–Heq, as suggested.
State-of-the-art nuclear magnetic resonance (NMR) selective experiments are capable of directly analyzing crude reaction mixtures. A new experiment named HD-HAPPY-FESTA yields ultrahigh-resolution ...total correlation subspectra, which are suitable for sign-sensitive determination of heteronuclear couplings, as demonstrated here by measuring the sign and magnitude for proton–fluorine couplings (JHF) from major and minor isomer products of a two-step reaction without any purification. Proton–fluorine couplings ranging from 51.5 to −2.6 Hz could be measured using HD-HAPPY-FESTA, with the smallest measured magnitude of 0.8 Hz. Experimental JHF values were used to identify the two fluoroketone intermediates and the four fluoroalcohol products. Results were rationalized and compared with the density functional theory (DFT) calculations. Experimental data were further compared with the couplings reported in the literature, where pure samples were analyzed.
The NMR analysis of fluorine-containing molecules, increasingly widespread due to their importance in pharmaceuticals and biochemistry, poses significant challenges. Severe peak overlap in the proton ...spectrum often hinders the extraction of critical structural information in the form of heteronuclear scalar coupling constants, which are crucial for determining pharmaceutical properties and biological activity. Here, a new method, IPAP-FESTA, is reported that drastically simplifies measurements of the signs and magnitudes of proton–fluorine couplings. Its usefulness is demonstrated for the structural study of the steroidal drug fluticasone propionate extracted from a commercial formulation and for assessing solvent effects on the conformational equilibrium in a physically inseparable fluorohydrin mixture.
This study expands the knowledge on the conformational preference of 1,3-amino alcohols in the gas phase and in solution. By employing Fourier transform infrared spectroscopy, nuclear magnetic ...resonance (NMR) spectroscopy, density functional theory (DFT) calculations, quantum theory of atoms in molecules (QTAIM), natural bond orbital (NBO) analysis, and molecular dynamics (MD), the compounds 3-aminopropan-1-ol (1), 3-methylaminopropan-1-ol (2), and 3-dimethylaminopropan-1-ol (3) are evaluated. The results show that the most stable conformation of each compound in the gas phase and in nonpolar solvents exhibited an O–H···N intramolecular hydrogen bond (IHB). Based on the experimental and theoretical OH-stretching frequencies, the IHB becomes stronger from 1 to 3. In addition, from the experimental NMR J-couplings, the IHB conformers are predominant in nonbasic solvents, representing 70–80% of the conformational equilibrium, while in basic solvents, such conformers only represent 10%. DFT calculations and QTAIM analysis in the gas phase support the occurrence of IHBs in these compounds. The MD simulation indicates that the non-hydrogen-bonded conformers are the lowest energy conformations in the solution because of molecular interactions with the solvent, while they are absent in the implicit solvation model based on density. NBO analysis suggests that methyl groups attached on the nitrogen atom affect the charge transfer energy involved in the IHB. This effect occurs mostly because of a decrease in the s-character of the LPN orbital along with weakening of the charge transfer from LPN to σ*OH, which is caused by an increase in the C–C–N bond angle.
Alkynyltrifluoroborate nucleophiles react smoothly with a wide range of sp 3-carbon electrophiles, including propargyl methanesulfonates and unactivated alkyl triflates, to give Sonogashira-type ...products, via a novel ion pair-assisted nucleophilic substitution mechanism. An ion pair–organic complex, investigated using computational chemistry and in situ NMR experiments, may play a crucial role in this reaction.
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