Paneth, Kant, and the philosophy of chemistry

Immanuel Kant has built up a dualistic epistemology that seems to fit to the peculiarities of chemistry quite well. Friedrich Paneth used Kant’s concept and characterised simple and basic substances which refer to the empirical and to the transcendental world, respectively. This paper takes account of the Kantian influences in Paneth’s philosophy of chemistry, and discusses pertinent topics, like observables, atomism and realism.

Systematic studies on the computation of nuclear magnetic resonance shielding constants and chemical shifts: the density functional models

We present a systematic density functional investigation on the prediction of the 13C, 15N, 17O, and 19F NMR properties of 23 molecules with 21 density functionals. Extensive comparisons are made for both 13C magnetic shieldings and chemical shifts with respect to the gas phase experimental data and the best CCSD(T) results. We find that the OPBE and OPW91 exchange-correlation functionals perform significantly better than some popular functionals such as B3LYP and PBE1PBE, even surpassing, in many cases, the standard wavefunction-based method MP2. Further analysis has been performed to explore the individual role played by various exchange and correlation functionals. We find that the B88 and PBE exchange functionals have a too strong tendency of deshielding, leading to too deshielded magnetic shielding constants; whereas the OPTX exchange functional performs remarkably well. We claim that the main source of error arises from the exchange functional, but correlation functional also makes important contribution. We find that the correlation functionals may be grouped into two classes. class A, such as LYP and B98, leads to deshielded NMR values, deteriorating the overall performance; whereas class B, such as PW91 and PBE, generally increases the absolute shieldings, which complements the exchange functionals, leading to improved results in the calculation of NMR data.     

1H chemical shifts in NMR: Part 22-Prediction of the 1H chemical shifts of alcohols, diols and inositols in solution, a conformational and solvation investigation

The (1)H NMR spectra of a number of alcohols, diols and inositols are reported and assigned in CDCl(3), D(2)O and DMSO-d(6) (henceforth DMSO) solutions. These data were used to investigate the effects of the OH group on the (1)H chemical shifts in these molecules and also the effect of changing the solvent. Inspection of the (1)H chemical shifts of those alcohols which were soluble in both CDCl(3) and D(2)O shows that there is no difference in the chemical shifts in the two solvents, provided that the molecules exist in the same conformation in the two solvents. In contrast, DMSO gives rise to significant and specific solvation shifts. The (1)H chemical shifts of these compounds in the three solvents were analysed using the CHARGE model. This model incorporates the electric field, magnetic anisotropy and steric effects of the functional group for long-range protons together with functions for the calculation of the two- and three-bond effects. The long-range effect of the OH group was quantitatively explained without the inclusion of either the C--O bond anisotropy or the C--OH electric field. Differential beta and gamma effects for the 1,2-diol group needed to be included to obtain accurate chemical shift predictions. For DMSO solution the differential solvent shifts were calculated in CHARGE on the basis of a similar model, incorporating two-bond, three-bond and long-range effects. The analyses of the (1)H spectra of the inositols and their derivatives in D(2)O and DMSO solution also gave the ring (1)H,(1)H coupling constants and for DMSO solution the CH--OH couplings and OH chemical shifts. The (1)H,(1)H coupling constants were calculated in the CHARGE program by an extension of the cos(2)phi equation to include the orientation effects of electronegative atoms and the CH--OH couplings by a simple cos(2)phi equation. Comparison of the observed and calculated couplings confirmed the proposed conformations of myo-inositol, chiro-inositol, quebrachitol and allo-inositol. The OH chemical shifts were also calculated in the CHARGE program. Comparison of the observed and calculated OH chemical shifts and CH.OH couplings suggested the existence of intramolecular hydrogen bonding in a myo-inositol derivative.     

探讨1,3丁二烯加成反应的机理、规律与应用*

结合2020年山东省高考题1,3丁二烯与HBr加成反应的势能变化示意图,利用学生已学的物质结构知识,适当、适度地介绍共轭效应,引导学生通过分析中间体的稳定性来认识1,2加成和1,4加成这2种加成方式;结合化学反应原理知识,引导学生理解控制温度等条件可以控制2种加成产物的比例;并对该加成反应规律进行了拓展与应用,以期为高中教学提供有益参考。     

1H chemical shifts in NMR. Part 27: proton chemical shifts in sulfoxides and sulfones and the magnetic anisotropy, electric field and steric effects of the SO bond

The (1)H chemical shifts of a series of sulfoxide and sulfone compounds in CDCl(3) solvent were obtained from experiment and the literature. These included dialkyl sulfoxides and sulfones (R(2)SO/R(2)SO(2), R = Me, Et, Pr, n-Bu), the cyclic compounds tetramethylene sulfoxide/sulfone, pentamethylene sulfoxide/sulfone and the aromatic compounds p-tolylmethylsulfoxide, dibenzothiopheneoxide/dioxide, E-9-phenanthrylmethylsulfoxide and (E) (Z)-1-methylsulfinyl-2-methylnaphthalene. The spectra of the pentamethylene SO and SO(2) compounds were obtained at -70 degrees C to obtain the spectra from the separate conformers (SO) and from the noninverting ring (SO(2)). This allowed the determination of the substituent chemical shifts (SCS) of the SO and SO(2) functional groups, which were analyzed in terms of the SO bond electric field, magnetic anisotropy and steric effect for long-range protons together with a model (CHARGE8d) for the calculation of the two and three bond effects. After parameterization, the overall root mean square (RMS) error (observed-calculated) for a dataset of 354 (1)H chemical shifts was 0.11 ppm. The anisotropy of the SO bond was found to be very small, supporting the dominant single bond S(+)--O(-) character of this bond.     

Tautomerism,protonation regioselectivity of 2-pyrrolidone and its complexation with palladium(II): an insight from the viewpoint of quantum chemistry

It has been established (AM1, PM3, RHF/6-31G**, MP2/6-31G**//RHF/6-31G**) that in the gaseous phase and in aqueous solution, the most thermodynamically stable tautomer of 2-pyrrolidone is lactame. According to PM3 evaluations with an explicit accounting for aqueous medium, the state of tautomeric equilibrium serves as a prerequisite to participation of 2-pyrrolidone's lactime tautomer (pyrroline-2-ol) in complexation with palladium(II) in aqueous solution. 2-Pyrrolidone protonation in the gaseous phase and in aqueous medium has been shown to proceed via the oxygen atom, corresponding to expectations on mesomeric displacement of electron density in the amide fragment. The aqueous medium stabilizes 2-pyrrolidone's lactime tautomer to a greater extent than for lactame, and an O-protonated cyclic amide compared to an N-protonated one. The stereodirective character of palladium(II) complexation with chloride ion and pyrroline-2-ol has been explained. The initially formed tetragonal–pyramidal adduct with an axial organic ligand rearranges into a precursor of the cis product, an intermediate with an extra coordinated axial chlorine atom. The less thermodynamically stable cis isomer of [PdCl₂(pyrroline-2-ol)₂] appears because its precursor is a lower energy intermediate of associative nucleophilic substitution. At a supramolecular level, cis product is capable of being stabilized by means of intermolecular dipole–dipole association in a crystal.     

Density functional calculations of 19F and 235U NMR chemical shifts in uranium (VI) chloride fluorides UF6−nCln: Influence of the relativistic approximation and role of the exchange‐correlation functional

Relativistic density functional theory (DFT) has been applied to the calculation of the ¹⁹F nuclear magnetic resonance (NMR) chemical shifts of the title compounds. It is shown that, while large‐core effective core potentials (ECP) fail completely for the calculation of ligand NMR chemical shifts in uranium compounds, small‐core ECPs are a valid relativistic method for this purpose. In an earlier study of the same systems, certain differences between theory and experiment had been observed, for instance, in the relative chemical shift of the A₄ and X sites in UF₅Cl. The reason for these deviations has been investigated further in the current paper. By comparing different relativistic methods, it is shown that the relativistic approximation is not responsible for these deviations. The role of the approximation to the exchange‐correlation (XC) functional of DFT has been probed, and generalized gradient approximations (GGA) as well as hybrid DFT methods have been investigated. None of these methods corrects the mentioned errors. It is argued that the neglect of environmental factors (solvent effects) remains as a possible error source, although the approximate XC functional appears to be the more likely cause of the problem. ²³⁵U NMR shieldings and chemical shifts have been calculated, and the trends predicted earlier have been confirmed. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

The Surface Analysis Working Group at the Consultative Committee for Amount of Substance,Metrology in Chemistry and Biology: A successful initiative by Martin Seah

Dr Martin Seah, NPL, was the initiator, founder, and first chairman of the Surface Analysis Working Group (SAWG) at the Consultative Committee for Amount of Substance, Metrology in Chemistry and Biology (CCQM) at the Bureau International des Poids et Mesures (BIPM), the international organization established by the Metre Convention. This tribute letter summarizes his achievements during his chairmanship and his long-running impact on the successful work of the group after his retirement.     

Toward a Consistent Interpretation of the QTAIM: Tortuous Link between Chemical Bonds,Interactions, and Bond/Line Paths

Currently, bonding analysis of molecules based on the Quantum Theory of Atoms in Molecules (QTAIM) is popular; however, “misinterpretations” of the QTAIM analysis are also very frequent. In this contribution the chemical relevance of the bond path as one of the key topological entities emerging from the QTAIM’s topological analysis of the one‐electron density is reconsidered. The role of nuclear vibrations on the topological analysis is investigated demonstrating that the bond paths are not indicators of chemical bonds. Also, it is argued that the detection of the bond paths is not necessary for the “interaction” to be present between two atoms in a molecule. The conceptual disentanglement of chemical bonds/interactions from the bonds paths, which are alternatively termed “line paths” in this contribution, dismisses many superficial inconsistencies. Such inconsistencies emerge from the presence/absence of the line paths in places of a molecule in which chemical intuition or alternative bonding analysis does not support the presence/absence of a chemical bond. Moreover, computational QTAIM studies have been performed on some “problematic” molecules, which were considered previously by other authors, and the role of nuclear vibrations on presence/absence of the line paths is studied demonstrating that a bonding pattern consistent with other theoretical schemes appears after a careful QTAIM analysis and a new “interpretation” of data is performed.     

1H NMR spectra. Part 30: 1H chemical shifts in amides and the magnetic anisotropy,electric field and steric effects of the amide group

The ¹H spectra of 37 amides in CDCl₃ solvent were analysed and the chemical shifts obtained. The molecular geometries and conformational analysis of these amides were considered in detail. The NMR spectral assignments are of interest, e.g. the assignments of the formamide NH₂ protons reverse in going from CDCl₃ to more polar solvents. The substituent chemical shifts of the amide group in both aliphatic and aromatic amides were analysed using an approach based on neural network data for near (≤3 bonds removed) protons and the electric field, magnetic anisotropy, steric and for aromatic systems π effects of the amide group for more distant protons. The electric field is calculated from the partial atomic charges on the N.C═O atoms of the amide group. The magnetic anisotropy of the carbonyl group was reproduced with the asymmetric magnetic anisotropy acting at the midpoint of the carbonyl bond. The values of the anisotropies Δχ_parl and Δχ_perp were for the aliphatic amides 10.53 and ?23.67 (×10^?6 ų/molecule) and for the aromatic amides 2.12 and ?10.43 (×10^?6 ų/molecule). The nitrogen anisotropy was 7.62 (×10^?6 ų/molecule). These values are compared with previous literature values. The ¹H chemical shifts were calculated from the semi‐empirical approach and also by gauge‐independent atomic orbital calculations with the density functional theory method and B3LYP/6–31G⁺⁺ (d,p) basis set. The semi‐empirical approach gave good agreement with root mean square error of 0.081 ppm for the data set of 280 entries. The gauge‐independent atomic orbital approach was generally acceptable, but significant errors (ca. 1 ppm) were found for the NH and CHO protons and also for some other protons. Copyright © 2013 John Wiley & Sons, Ltd.     

Rhorix: An interface between quantum chemical topology and the 3D graphics program blender

Chemical research is assisted by the creation of visual representations that map concepts (such as atoms and bonds) to 3D objects. These concepts are rooted in chemical theory that predates routine solution of the Schrödinger equation for systems of interesting size. The method of Quantum Chemical Topology (QCT) provides an alternative, parameter‐free means to understand chemical phenomena directly from quantum mechanical principles. Representation of the topological elements of QCT has lagged behind the best tools available. Here, we describe a general abstraction (and corresponding file format) that permits the definition of mappings between topological objects and their 3D representations. Possible mappings are discussed and a canonical example is suggested, which has been implemented as a Python “Add‐On” named Rhorix for the state‐of‐the‐art 3D modeling program Blender. This allows chemists to use modern drawing tools and artists to access QCT data in a familiar context. A number of examples are discussed. © 2017 The Authors. Journal of Computational Chemistry Published by Wiley Periodicals, Inc.     

ChemInform Abstract: Local Density Functional Study of Copper Clusters: A Comparison Between Real Clusters,Model Surface Clusters,and the Actual Metal Surface.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Saturated amine oxides: Part 8. Hydroacridines: Part 27. Effects of N-oxidation and of N-quaternization on the 15N NMR chemical shifts of N-methylpiperidine-derived mono-, bi-, and tricycloaliphatic tertiary amines

The (15)N chemical shifts of 13 N-methylpiperidine-derived mono-, bi- and tricycloaliphatic tertiary amines, their methiodides and their N-epimeric pairs of N-oxides were measured, and the contributions of specific structural parameters to the chemical shifts were determined by multilinear regression analysis. Within the examined compounds, the effects of N-oxidation upon the (15)N chemical shifts of the amines vary from +56 ppm to +90 ppm (deshielding), of which approx. +67.7 ppm is due to the inductive effect of the incoming N(+)--O(-) oxygen atom, whereas the rest is due to the additive shift effects of the various C-alkyl substituents of the piperidine ring. The effects of quaternization vary from -3.1 ppm to +29.3 ppm, of which approx. +8.9 ppm is due to the inductive effect of the incoming N(+)--CH(3) methyl group, and the rest is due to the additive shift effects of the various C-alkyl substituents of the piperidine ring. The shift effects of the C-alkyl substituents in the amines, the N-oxides and the methiodides are discussed.     

Relativistic effects and the halogen dependencies in the 13C chemical shifts of CH4−nIn,CH4−nBrn,CCl4−nIn,and CBr4−nIn (n=0–4)

Linear and nonlinear halogen dependencies of the ¹³C magnetic shielding constants of CH_4−nI_n, CH_4−nBr_n, CCl_4−nI_n, and CBr_4−nI_n were fairly reproduced by the ab initio generalized unrestricted Hartree–Fock (GUHF)/finite perturbation (FP) method including spin‐orbit (SO) interaction and spin‐free relativistic (SFR) terms. As seen from the experimental trends, the calculated ¹³C chemical shifts in CCl_4−nI_n and CBr_4−nI_n depend linearly on n=0–4, while those in CH_4−nI_n and CH_4−nBr_n depend nonlinearly. We found that both the linear and nonlinear dependencies are due to the relativistic effects, and especially due to the Fermi–Contact (FC) term originating from the SO interaction. © 2001 John Wiley & Sons, Inc. J Comput Chem 22: 528–536, 2001     

ChemInform Abstract: Comparative Studies on the Phase Stability,Electronic Structure,and Topology of the Charge Density in the Li3XO4 (X: P,As, V) Lithium Orthosalt Polymorphs

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

Density functional computations of 99Ru chemical shifts: relativistic effects, influence of the density functional, and study of solvent effects on fac-[Ru(CO)3I3]-

Solvent effects on the 99Ru NMR chemical shift of the complex fac-[Ru(CO)3I3]- are investigated computationally using density functional theory. Further, benchmark calculations of the 99Ru shift for a set of ten Ru complexes have been performed in order to calibrate the computational model and to determine the importance of relativistic effects on the 99Ru nuclear magnetic shielding and on the chemical shift. A computational model for fac-[Ru(CO)3I3]- that includes both explicit solvent molecules and a continuum model is shown to yield the best agreement with experiment. Relativistic corrections are shown to be of minor importance for determining 99Ru chemical shifts. On the other hand, the nature of the density functional is of importance. In agreement with literature data for ligand trends of 99Ru chemical shifts, the chemical shift range for different solvents is also best reproduced by a hybrid functional.     

ChemInform Abstract: Chemical Bonding in the Ternary Transition Metal Bismuthides Ti4MBi2 with M: Cr,Mn, Fe,Co, and Ni

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.