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Treating 195Pt nuclear magnetic resonance parameters in solution remains a considerable challenge from a quantum chemistry point of view, requiring a high level of theory that simultaneously takes into account the relativistic effects, the dynamic treatment of the solvent–solute system, and the dynamic electron correlation. A combination of Car-Parrinello molecular dynamics (CPMD) and relativistic calculations based on two-component zeroth order regular approximation spin–orbit Kohn–Sham (2c-ZKS) and four-component Dirac–Kohn–Sham (4c-DKS) Hamiltonians is performed to address the solvent effect (water) on the conformational changes and J PtPt 1 coupling. A series of bridged PtIII dinuclear complexes [L1–Pt2(NH3)4(Am)2–L2]n+ (Am = α–pyrrolidonate and pivalamidate; L = H2O, Cl−, and Br−) are studied. The computed Pt–Pt coupling is strongly dependent on the conformational dynamics of the complexes, which, in turn, is correlated with the trans influence among axial ligands and with the angle N–C–O from the bridging ligands. The J-coupling is decomposed in terms of dynamic contributions. The decomposition reveals that the vibrational and explicit solvation contributions reduce J PtPt 1 of diaquo complexes (L1 = L2 = H2O) in comparison to the static gas-phase magnitude, whereas the implicit solvation and bulk contributions correspond to an increase in J PtPt 1 in dihalo (L1 = L2 = X−) and aquahalo (L1 = H2O; L2 = X−) complexes. Relativistic treatment combined with CPMD shows that the 2c-ZKS Hamiltonian performs as well as 4c-DKS for the J PtPt 1 coupling. [ABSTRACT FROM AUTHOR]

Glyphosate is a widely used herbicide, and its protonation and deprotonation sites are fundamental to understanding its properties. In this work, the sodiated, protonated, and deprotonated glyphosate were evaluated in the gas phase by infrared multiple photon dissociation spectroscopy to determine the exact nature of these coordination, protonation, and deprotonation states in the gas phase. In this context, Natural Bond Orbital analyses were carried out to unravel interactions that govern glyphosate (de)protonation states in the gas phase. The solvent effect on the protonation/deprotonation equilibria was also investigated by implicit (Solvation Model Based on Density and polarizable continuum models) and explicit solvation models (Monte Carlo and Molecular Dynamics simulations). These results show that glyphosate is protonated in the phosphonate group in the gas phase because of the strong hydrogen bond between the carboxylic oxygen (O7) and the protonated phosphonate group (O8–H19), while the most stable species in water is protonated at the amino group because of the preferential interaction of the NH2+ group and the solvent water molecules. Similarly, deprotonated glyphosate [Glyp−H]− was shown to be deprotonated at the phosphonate group in the gas phase but not in solution, also because of the preferential solvation of the NH2+ group present in the other deprotomers. Therefore, these results show that the stabilization of the protonated amino group by the solvent molecules is the governing factor of the (de)protonation equilibrium of glyphosate in water. [ABSTRACT FROM AUTHOR]

The Diels–Alder reaction of three chiral dihydro‐2H‐[2,3‐a]oxazolopyridines with N‐methylmaleimide afforded the corresponding chiral cycloadducts as diastereomeric mixtures. In the presence of a solvent, some of the originally formed adducts underwent isomerisation to new isoquinuclidines. [ABSTRACT FROM AUTHOR]

We report the structural, vibrational, and optical properties of americium formate (Am(CHO2)3) crystals synthesized via the in situ hydrolysis of dimethylformamide (DMF). The coordination polymer features Am3+ ions linked by formate ligands into a three‐dimensional network that is isomorphous to several lanthanide analogs, (e. g., Eu3+, Nd3+, Tb3+). Structure determination revealed a nine‐coordinate Am3+ metal center that features a unique local C3v symmetry. The metal–ligand bonding interactions were investigated by vibrational spectroscopy, natural localized molecular orbital calculations, and the quantum theory of atoms in molecules. The results paint a predominantly ionic bond picture and suggest the metal‐oxygen bonds increase in strength from Nd−O

An ab initio molecular dynamics investigation of the solvent effect (water) on the structural parameters, 195Pt NMR spin–spin coupling constants (SSCCs) and chemical shifts of a series of pyridonate-bridged PtIII dinuclear complexes is performed using Kohn–Sham (KS) Car–Parrinello molecular dynamics (CPMD) and relativistic hybrid KS NMR calculations. The indirect solvent effect (via structural changes) has a dramatic effect on the 1JPtPt SSCCs. The complexes exhibit a strong trans influence in solution, where the Pt–Pt bond lengthens with increasing axial ligand σ-donor strength. In the diaqua complex, where the solvent effect is more pronounced, the SSCCs averaged for CPMD configurations with explicit plus implicit solvation agree much better with the experimental data, while the calculations for static geometry and CPMD unsolvated configurations show large deviations with respect to experiment. The combination of CPMD with hybrid KS NMR calculations provides a much more realistic computational model that reproduces the large magnitudes of 1JPtPt and 195Pt chemical shifts. An analysis of 1JPtPt in terms of localized and canonical orbitals shows that the SSCCs are driven by changes in the s-character of the natural atomic orbitals of Pt atoms, which affect the 'Fermi contact' mechanism. [ABSTRACT FROM AUTHOR]

Microreactor technology is increasingly applied in the chemical‐pharmaceutical industry for safer and more efficient drug production as compared to the traditional batch process. This technology is employed for the first time to study the production of 2‐[methyl(pyridin‐2‐yl)amino]ethanol, the first intermediate in rosiglitazone synthesis. Under the optimum operating conditions, a single microreactor chip at 160 °C allowed to produce the equivalent of more than five batch reactors at 120 °C. The kinetic study indicated that the reaction is second order. Thermodynamic parameters were determined by the Eyring equation and density functional theory (DFT) calculations with good agreement. DFT results suggested a concerted nucleophilic aromatic substitution reaction mechanism. [ABSTRACT FROM AUTHOR]

The indirect nuclear spin-spin coupling constants of homogeneous hydrogen-bonded HCN clusters are compared with those of inhomogeneous HCN clusters where one of the terminal HCN molecules is substituted by its isomer HNC and by LiCN. Both the intra- and intermolecular (across the hydrogen bond) coupling constants are calculated for the linear form of the clusters containing up to three molecular monomers using different hybrid DFT functionals. The geometry of the monomers and clusters is optimised at the B3LYP/6-311++G(d,p) level. The effect of substitution by the ionic compound LiCN on the coupling constants of HCN is found to be more pronounced than that by HNC. The Ramsey parameters that form the total spin-spin coupling constants are also analysed individually. Among the four Ramsey parameters, the Fermi Contact term is found to be the dominant contributor to the total coupling constants in most cases. The presence of LiCN in the cluster tends to decrease the intramolecular Fermi Contact values, while HNC increases the same in all dimers and trimers. The contributions of localised molecular orbitals have been analysed for the HCN-HNC cluster to obtain some additional insight about the SSCC transmission mechanism along the coupling pathway. [ABSTRACT FROM AUTHOR]

Four new [Pu(iv)Cln(NO3)6−n]2− (n = 0, 2, 3) and [Pu(vi)O2Cl3(NO3)]2− containing materials were crystallized from acidic, aqueous media and structurally characterized. The anions are assembled via hydrogen and halogen bonding motifs, which are rationalized computationally. The Pu–NO3 and –Cl bonds were probed using QTAIM and NLMO analyses and found to be polar and largely ionic. [ABSTRACT FROM AUTHOR]

Recent research [Chem. Sci., 2017, 8, 6570–6576] showed for R-substituted benzenes with R = NH2, NO2 that the substitution effects on the 13C NMR chemical shifts are correlated with changes in the σ-bonding framework and do not follow directly the electron-donating or -withdrawing effects on the π orbitals. In the present work we extend the study to halogen (X = F, Cl, Br or I) substituted R-benzenes. The effect of X and R groups on 13C NMR chemical shifts in X–R-benzenes are investigated by density functional calculations and localized molecular orbital analyses. Deshielding effects caused by the X atom on the directly bonded carbon nucleus are observed for F and Cl derivatives due to a paramagnetic coupling between occupied π orbitals and unoccupied UGRAPHIC DISPLAY="INLINE" ID="UGT1" SRC="UGT1"/ antibonding orbitals. The SO coupling plays an important role in the carbon magnetic shielding of Br and I derivatives, as is well known, and the nature of X also modulates the 13C paramagnetic shielding contributions. Overall, the X and R substituent effects are approximately additive. [ABSTRACT FROM AUTHOR]

Crystals of a hydrated Pu(iii) chloride, (C5H5NBr)2[PuCl3(H2O)5]·2Cl·2H2O, were grown via slow evaporation from acidic aqueous, high chloride media. X-ray diffraction data reveals the neutral [PuCl3(H2O)5] tecton is assembled via charge assisted hydrogen and halogen bonds donated by 4-bromopyridinium cations and a series of inter-tecton hydrogen bonds. [ABSTRACT FROM AUTHOR]

The mechanisms of a tetrasubstituted imidazole [2-(2,4,5-triphenyl-1 H-imidazol-1-yl)ethan-1-ol] synthesis from benzil, benzaldehyde, ammonium acetate, and ethanolamine in [Et2NH2][HSO4] ionic liquid (IL) are studied computationally. The effects of the presence of the cationic and anionic components of the IL on transition states and intermediate structures, acting as a solvent versus as a catalyst, are determined. In IL-free medium, carbonyl hydroxylation when using a nucleophile (ammonia) proceeds with a Gibbs free energy (Δ G≠) barrier of 49.4 kcal mol−1. Cationic and anionic hydrogen-bond solute-solvent interactions with the IL decrease the barrier to 35.8 kcal mol−1. [Et2NH2][HSO4] incorporation in the reaction changes the nature of the transition states and decreases the energy barriers dramatically, creating a catalytic effect. For example, carbonyl hydroxylation proceeds via two transition states, first proton donation to the carbonyl (Δ G≠=9.2 kcal mol−1) from [Et2NH2]+, and then deprotonation of ammonia (Δ G≠=14.3) via Et2NH. Likewise, incorporation of the anion component [HSO4]− of the IL gives comparable activation energies along the same reaction route and the lowest transition state for the product formation step. We propose a dual catalytic IL effect for the mechanism of imidazole formation. The computations demonstrate a clear distinction between IL solvent effects on the reaction and IL catalysis. [ABSTRACT FROM AUTHOR]

The dependence of the magnitude and sign of 3JHFF on the bond angle in fluoro-cycloalkene compounds is evaluated by electronic structure calculations using different levels of theory, viz. DFT, SOPPA(CCSD) and SOPPA(CC2). Localized molecular orbital contributions to 3JHFF are analyzed to assess which orbitals are responsible for 3JHFF and which are the most important coupling transmission mechanisms for each compound. Fluoro-ethylene is used as a model system to evaluate the dependence of the 3JHFF coupling constant on the angle between the σCα–F and σCα′–HF vectors. Through-space and hyperconjugative transmission pathways and ring strain are identified as responsible for the opposite trend between 3JHFF and bond angle, and for the negative signs obtained for the two molecules, respectively. One of the fluorine lone pairs, σCα′–HF, σCα–F, σCα′–Cβ′ bonding orbitals and the σ*Cα–F antibonding orbital are involved in the J-coupling pathways, according to analyses of pairwise-steric and hyperconjugative energies. [ABSTRACT FROM AUTHOR]

In this study, stereoelectronic interactions were considered to explain the experimental difference in the magnitude of the known heavy-atom effect on the 13C NMR chemical shifts in cis- and trans-1,2-dihaloethene isomers (halo = F, Cl, Br or I). The experimental values were compared to the calculated values with various DFT functionals using both the nonrelativistic approach (NR) and the relativistic approximations SR-ZORA (SR) and SO-ZORA (SO). NBO and NLMO contributions to the 13C NMR shielding tensors were determined to assess which stereoelectronic interactions have a more important effect on the shielding tensor in each principal axis system (PAS) coordinate. These analyses associated with the orbital rotation model and the HOMO–LUMO energy gap enable rationalization of trends between cis and trans isomers from fluorine to iodine derivatives. Both paramagnetic and SO shielding terms were responsible for the observed trends. It was possible to conclude that the steric interactions between the two iodine atoms and the hyperconjugative interactions involving the halogen lone pairs (LP(X)) and πC=C*, σC=C* and σC–X* antibonding orbitals are responsible for the lower 13C NMR shielding for the cis isomers of the bromine and the iodine compounds than that of the trans isomers. [ABSTRACT FROM AUTHOR]

Tryptophan and phenylakylamines (PAAs) are important biomolecules, which are involved in a myriad of processes. These molecules have been experimentally reported to exhibit N–H+...π interactions in their protonated form; however, this has not been theoretically investigated in detail. Generally, such interactions are observed in diverse biological systems, and their evaluation would be useful for understanding protein folding and functioning. Therefore, in this study, we have described the N–H+...π interactions of the abovementioned classes of molecules using the Quantum Theory of Atoms In Molecules (QTAIM), Natural Bond Orbital (NBO), and Non-Covalent Interaction (NCI) analyses. The results of our N–H+...π interaction energy calculations were consistent with the experimental energies derived from the redshift of the vibrational stretches. The energy values obtained using the QTAIM-based Espinosa's approach provided a relatively better result than similar approaches previously reported in the literature. Furthermore, we observed that the N–H+...π interaction energy in tryptophan is weaker than the resonance-assisted hydrogen bond energy of the N–H+...O=C interactions of its three most stable conformers accessible at room temperature. In contrast, the strength of the N–H+...π interaction in PAAs was observed to increase with increasing alkyl lateral chain length. The increased flexibility of longer chains increases the distance between nitrogen and the phenyl ring without disturbing the N–H+...π interaction. [ABSTRACT FROM AUTHOR]