硫叶立德化合物优势构型和键结构的量子拓扑研究

采用MP4（SDTQ）/6-311++G（d,p）和B3LYP/6-311++G（d,p）对所选四种化合 物进行构型优化，从量子拓扑学的角度对各稳定构型进行电子密度拓扑分析，讨论 了C-S键的特性。研究发现：（1）类硫叶立德自由基（·CHSH_2）和硫叶立德（ CH_2SH_2）基态的稳定构型都不具有C_s对称性；（2）类硫叶立德自由基和硫叶立 德中C-S键的性质类似，硫叶立德中π键由两个电子形成，类硫叶立德自由基中π 键由一个电子形成，所以前者的π键性质明显，后者的π键性质不明显；（3）类 硫叶立德自由基（·CHSH_2）中单电子π键中的电子主要在碳原子附近运动，属于 单电子π（C → S）配键，所以其C-S键的强度比相应的产物要弱。     

Thiophenols,Promising Scavengers of Peroxyl Radicals: Mechanisms and kinetics

The activity of 12 thiophenols as primary antioxidants in aqueous solution has been studied using density functional theory. Twelve different substituted thiophenols were tested as peroxyl radicals scavengers. Single electron transfer (SET) and formal hydrogen transfer (FHT) were investigated. The SET mechanism was found to be the main mechanism, with rate constants that are close to the diffusion limit, which means that these thiophenolic compounds have the capacity to scavenge peroxyl radicals before they can damage biomolecules. All 12 thiophenolic compounds react faster with methylperoxyl than with hydroperoxyl radicals. In addition, it was found that pH plays an important role in the reactivity of these compounds. © 2019 Wiley Periodicals, Inc.     

A study of the electronic structure and properties of the propargyl radical

By means of B3LYP/6-311++G(3df,3pd) the electron density distribution in the propargyl radical CH₂CCH is obtained. Within the Quantum Theory of Atoms in Molecules the phenomenon of conjugation and the spin density distribution of the unpaired electron in CH₂CCH are studied at the qualitative level. Characteristics of the electronic structure of CH₂CCH and its parent molecules CH₃–C≡CH and CH₂=C=CH₂ are compared. With the use of the rigid rotator-anharmonic oscillator model the thermodynamic properties of the propargyl radical and enthalpies of bond cleavage in propyne and allene are calculated in the temperature range 298-1500 K. The relationship between the electronic and thermodynamic properties of CH₂CCH is considered and its conjugation energy is calculated.     

Electronic structure of crystalline uranium nitride: LCAO DFT calculations

The results of electronic structure calculations performed for the first time for crystalline uranium nitride and using a LCAO basis are discussed. For calculations we used the density functional method with the PW91 exchange correlation potential and a variety of relativistic core potentials for the uranium atom. The calculated atomization energy of the crystal agrees well with the experimental data and with the results of calculations with the plane wave basis. It is shown that a chemical bond in crystalline uranium nitride is a metal covalent bond. The metal component of the bond is due to the 5f electrons localized on the uranium atom and having energies near the Fermi level and the bottom of the conduction band. The covalent component of the chemical bond results from an overlap between the uranium 6d and 7s valence orbitals and the nitrogen 2p atomic orbitals. Inclusion of the 5f electrons in the core of the uranium atom introduces relatively minor changes in the calculated binding energy and electron density distribution.     

The C–H bond dissociation enthalpies in fused N-heterocyclic compounds

The C–H bond dissociation enthalpies (BDEs) of the 26 N, O, S-containing mono-heterocyclic compounds were evaluated using the composite high-level ab initio methods G3 and G4. The C–H BDEs for 32 heterocyclic compounds were calculated using 8 types of density functional theory (DFT) methods. Comparing with the experimental values, the BMK method gave the lowest root mean square error (RMSE) of 7.2 kJ/mol. Therefore, the C–H BDEs of N-fused-heterocyclic compounds at different positions were investigated by the BMK method. By NBO analysis two linear relationships between the C–H BDEs of quinoline and isoquinoline with natural charges qC/e in molecules and with natural charges qC/e in radicals were found. The substituent effects on C_(α)–H BDEs in N-fused-heterocyclic compounds were also discussed. It was found that there are two linear relationships between the C_(α)–H BDEs of quinoline and isoquinoline derivatives with natural charges qC_(α)/e for the EDGs and CEGs substituents.     

Propagator quantum chemical study of <Emphasis Type="Italic">S</Emphasis>-<Emphasis Type="Italic">cis</Emphasis>-(<Emphasis Type="Italic">Z</Emphasis>)-2-(2-formylethenyl)pyrrole: electronic structure and aspects of intramolecular hydrogen bond manifestation in ionization spectra

For the purpose of investigation of the electronic structures of functionalized pyrroles with potential biological activity the electronic structures and ionization spectra of S-cis-(Z)-2-(2-formylethenyl)pyrrole (FP) were calculated by the propagator quantum chemical method. The calculations were performed using the third-order algebraic diagrammatic construction method (ADC(3)) for one-particle Green´s function (electronic propagator) and the 6–31G** basis set. Going from FP (possessing the intramolecular hydrogen bond H?O) to its conformation FPR (without H?O bonding), the O1s-ionization energy and the ionization energy of the σ-type lone electron pair orbital of the O atom decrease by ~0.2 eV, which is a consequence of stopping the electron density transfer from the O atom. A strong electron density transfer through the hydrogen bond from the O atom to the NH group occurs in the nitrogen core level ionization spectrum as evidenced by a lower N1s-ionization energy of FP (by ~0.7 eV ) compared to that of FPR. The valence shell ionization spectra of FP and FPR calculated using the ADC(3) method are characterized by a high density of the satellite states. The results obtained indicate that the electronic structures of the compounds of the considered class are characterized by pronounced effects of electron correlation.     

Computational studies of σ-type weak interactions between NCO/NCS radicals and XY(X = H,Cl;Y = F,Cl,and Br)

The triatomic radicals NCO and NCS are of interest in atmospheric chemistry,and both the ends of these radicals can potentially serve as electron donors during the formation of σ-type hydrogen/halogen bonds with electron acceptors XY(X = H,Cl;Y = F,Cl,and Br).The geometries of the weakly bonded systems NCO/NCS···XY were determined at the MP2/aug-cc-pVDZ level of calculation.The results obtained indicate that the geometries in which the hydrogen/halogen atom is bonded at the N atom are more stable than those where it is bonded at the O/S atom,and that it is the molecular electrostatic potential(MEP)-not the electronegativity-that determines the stability of the hydrogen/halogen bond.For the same electron donor(N or O/S) in the triatomic radical and the same X atom in XY,the bond strength decreases in the order Y = F > Cl > Br.In the hydrogen/halogen bond formation process for all of the complexes studied in this work,transfer of spin electron density from the electron donor to the electron acceptor is negligible,but spin density rearranges within the triatomic radicals,being transferred to the terminal atom not interacting with XY.     

Raman spectroscopy of short-lived terthiophene radical cations generated by photochemical and chemical oxidation.

The Raman spectra of various terthiophene radical cations are investigated; namely those of unsubstituted terthiophene and two styryl-substituted terthiophenes. Transient pump-probe resonance Raman spectroscopy is used to measure the short-lived radical cation spectra of non-end-capped 2,2':5',2'-terthiophene (3T) and 3'-[(E)-2-(4-nitrophenyl)ethenyl]-2,2':5',2'-terthiophene (NO2-pe3T). For these two compounds, the radical cations are generated via either direct photogeneration or photochemically using the electron acceptor tetracyanoethylene. The radical cation of 5,5'-dimethyl-3'-[(E)-2-phenylethenyl]-2,2':5',2'-terthiophene (DM-pe3T) is stable for up to five minutes as a result of the two alpha end caps and continuous-wave resonance Raman spectroscopy and chemical oxidation is used to obtain the spectrum of this radical cation. The resonance Raman spectra of all three terthiophene radical cations are dominated by a group of very intense bands in the low-frequency region. These bands have been assigned, by density functional theory methods, to C-S stretching modes coupled to thiophene ring deformations. These modes are significantly less intense in the sigma-dimer of NO2-pe3T [i.e. the corresponding styryl sexithiophene (NO2-pe3T)2]. This observation is attributed to a smaller change in the C--S bond order in the sexithiophene compared to the analogous terthiophene. This bond order difference may be rationalised by consideration of the singly occupied molecular orbital and lowest unoccupied molecular orbital, which are involved in the electronic transition probed by the laser excitation wavelength.     

NCO/NCS自由基与XY（X=H,Cl;Y=F,Cl,Br）间σ-型弱作用的理论研究

NCO和NCS是大气化学中非常引人关注的自由基,它们均有三个原子并且两个端基原子均可作为电子给体形成σ-型氢/卤键.本文在MP2/aug-cc-pVDZ水平上研究了NCO/NCS...XY（X=H,Cl;Y=F,Cl,Br）体系中的弱化学键.计算结果表明,氢/卤原子与N原子相连形成的复合物比与O/S原子相连形成的复合物稳定;氢/卤键的稳定性由分子静电势决定,而非原子电负性;对相同的电子给体B（B=N,O/S）和相同的卤原子来说,化学键的强度按Y=F,Cl,Br的顺序逐渐减弱.在氢/卤键形成过程中,自旋电子密度在电子给体和电子受体间的转移较少,但它在自由基内部发生重排,就本文研究的所有复合物而言,自旋电子密度均转移向XY分子的相反位置.     

A DFT Study on Intramolecular Hydrogen Bond in Substituted Catechols and Their Radicals

Density functional theory(DFT)at B3LYP/6-31G(d,p) level was employed to calculate intramolecular hydrogen bond enthalpies (H1HB),O-H charge differencces,O-H bond lengths and bond orders for various substituted catechols and their radicals generated after H-abstraction.It was found that although the charge difference between hydrogen-bonded H and O played a role in determining H1HB,H1HB was mainly governed by the hydrogen bond length.As the oxygen-centedred radiocal has great tendency to form a chemical bond with the H atom,hydrogen bond lengths in catechloic radicals are systematically shorter than those in catechlos,hence,the H1HB for the former are higher than those for the latter.     

A new method of determination of radii of ions with arbitrary effective charges

An equation for calculation of the radii of ions with an arbitrary effective charge has been derived. The ionic radii of halogens, chalcogens, and other atoms with different charges have been calculated. Under the assumption of pure ionic bond character, these values have been used for calculating the R ₁₂ distances for a large group of different molecules—halogens, interhalides, oxygen, chalcogens, and nitrogen and their compounds—by the previously derived equation for the a priori determination of internuclear distances. The error of calculation of the internuclear distance for halogens and interhalides is no more than 0.07 Å (3–4%). The internuclear distance in dihalogen cations Hal ₂ ⁺ and binary ionic molecules of p elements and their oxides and sulfides have been calculated. It has been demonstrated that the coordination (environment) of atoms should be taken into account and that there is a possibility of estimating the bond multiplicity and the character of bonding electron pairs in a molecule.     

Theoretical and Experimental Investigation of the 2-Hydroxyquinoxaline Structure: Study of the Tautomerization Equilibrium System and Analysis of the Electronic Properties

All reasonable tautomers of 2-hydroxyquinoxaline (2HQ) are investigated by the DFT B3LYP/6-311G(d) method. The optimized geometries corresponding to the minimum energy show that the keto form QX2 is the most stable form. The geometry optimization parameters (bond lengths, bond angles) are compared to the X-ray values. Calculated FTIR, UV, and NMR spectra of QX2 are compared to the experimental data to achieve a synergetic computational and spectroscopic approach for the structure analysis of 2HQ. The electronic properties, frontier molecular orbitals, and Mulliken atomic charges are calculated.     

Effect of the structure of alkoxy radicals on the mass-spectral fragmentation of dialkyl alkylphosphonates

Basic fragmentation reaction of dialkyl alkylphosphinates under the conditions of electron ionization proceeds in two steps. In the first step occurs cleavage of C-O bond and splitting the olefin radical off. The intermediate ion formed therewith exerts further fragmentation by the similar way. Peaks of the intermediate ions occurs in the spectra of all dialkyl alkylphosphonates except O-methyl derivatives. In the case of branching at α-carbon atoms of alkoxy radicals cleavage of the first carbon-carbon bond of the alkoxy radical unlike the case of alkyl fluorophosphonates, in the intermediate ion rather than in molecular ion and accompanied by the elimination of alkane. These found regularities allow to explain principal fragmentation pathways of a wide series of phosphoric acids esters of general formula (RO) _n P(O)X _n?3 (where X is R, Hal, or OMe) with both linear and branched in α-position alkoxy radicals.     

Quelques considérations sur la structure électronique du naphtalène

Theπ electronic structure of naphtalene is studied, using a semi-empirical approximation for coulombic and resonance integrals; forH andS (H, hamiltonian;S, overlap) the complete matrices are adopted, together withKohlrausch's nuclear effective charges. A non uniform charge distribution is obtained, with charge accumulation at the tertiary carbons. Bond orders between non neighboring atoms indicate contributions to the fundamental state from other structures besides the classical ones. A comparative study of the obtained interatomic distances is carried. It is shown that [H, S]=0 is not a sufficient condition for the identity of the bond orders for the fundamental state calculated with and without overlap.     

Structural and electronic properties of heptachlor

In this work, the molecular geometry of heptachlor is investigated using ab initio HF, DFT, LDA, and GGA methods. The natural bond orbital (NBO) analysis is performed at the B3LYP/6-311++G(d,p) level of theory. The first order hyperpolarizability β_total, the mean polarizability Δα, the anisotropy of the polarizability Δα, and the dipole moment μ, are calculated by B3LYP/6-311++G(d,p) and HF/6- 311++G(d,p) methods. The first order hyperpolarizability (β_total) is calculated based on the finite field approach. UV spectral parameters along with HOMO, LUMO energies for heptachlor are determined in vacuum and the solvent phase using HF, DFT, and TD-DFT/B3LYP methods implemented with the 6-311++G(d,p) basis set. Atomic charges and electron density of heptachlor in vacuum and ethanol are calculated using DFT/B3LYP and TD-DFT/B3LYP methods and the 6-311++G(d,p) basis set. In addition, after the frontier molecular orbitals (FMOs), the molecular electrostatic potential (MEP), the electrostatic potential (ESP), the electron density (ED), and the solvent accessible surface of heptachlor are visualized as a results of the B3LYP/6-311++G(d,p) calculation. Densities of states (DOS), the external electric field (EF) effect on the HOMO-LUMO gap, and the dipole moment are investigated by LDA and GGA methods.     

Intramolecular hydrogen bond in the hydroxycyclohexadienyl peroxy radicals

The hydroxycyclohexadienyl peroxy radicals (HO? C₆H₆? O₂) produced from the reaction of OH‐benzene adduct with O₂ were studied with density functional theory (DFT) calculations to determine their characteristics. The optimized geometries, vibrational frequencies, and total energies of 2‐hydroxycyclohexadienyl peroxy radical II_s and 4‐hydroxycyclohexadienyl peroxy radical III_s were calculated at the following theoretical levels, B3LYP/6‐31G(d), B3LYP/6‐311G(d,p), and B3LYP/6‐311+G(d,p). Both were shown to contain a red‐shifted intramolecular hydrogen bond (O? H … O? H bond). According to atoms‐in‐molecules (AIM) analysis, the intramolecular hydrogen bond in the 2‐hydroxycyclohexadienyl peroxy radical II_s is stronger than that one in 4‐hydroxycyclohexadienyl peroxy radical III_s, and the former is the most stable conformation among its isomers. Generally speaking, hydrogen bonding in these radicals plays an important role to make them more stable. Based on natural bond orbital (NBO) analysis, the stabilization energy between orbitals is the main factor to produce red‐shifted intramolecular hydrogen bond within these peroxy radicals. The hyperconjugative interactions can promote the transfer of some electron density to the O? H antibonding orbital, while the increased electron density in the O? H antibonding orbital leads to the elongation of the O? H bond and the red shift of the O? H stretching frequency. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Investigation of the Electronic Structure of Alkyl Allyl Radicals

The electronic structure of the homologous series of CH₃(CH₂)_nCHCHCH₂ (n = 0÷5) allyl all radicals is studied. The obtained spin density distribution is used to determine the fragment serving as the radical center. The delocalization of spin density over the basin of the radical center is shown to be responsible for two free valencies associated with two classical canonical structures (the conjugated fragment). The conjugation phenomenon is studied and electronic parameters are determined for the “standard” conjugated fragment CHCHCH₂.     

XPS spectra of free nitroxyl radicals and their electronic structure

The N(1s) and O(1s) XPS spectra of stable nitroxyl radicals and molecules with a related heterocycle structure: 4,4,5,5-tetramethyl-2-phenyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, 4,4,5,5-tetramethyl-2-(3-nitrophenyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, 4,4,5,5-tetramethyl-2-(2-hydroxyphenyl)-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl, 4,4,5,5-tetramethyl-2-(2-hydroxy-3-nitrophenyl)-4,5-dihydro-1Himidazole-3-oxide-1-oxyl, and 4,4,5,5-tetramethyl-2-phenyl-4,5-dihydro-1H-imidazole-3-oxide were studied. The possibility to apply X-ray electron spectra for investigation of the charge electron and spin density distribution on free radical atoms and at their coordination by a metal is considered.     

Electron affinity and substituent effects in radical anions

The first vertical electron affinities EA of 13 series of molecules and free radicals D(X _i ) _n are related to the inductive (σ _I ), resonance (σ _R ^? ), and polarization (σ_α) parameters of substituents X _i by the dependences EA = EA _H + aΣσ _I + bΣσ _R/? + cΣσ_α: In radical anions D^+·(X _i ) _n , compared to radical cations D^+·(X _i ) _n , the polarization interaction is weaker or similar in magnitude but has an opposite sign. The previously unknown resonance parameters σ _R ^? of substituents SiMe₃ and CH₂SiMe₃ bound to the radical anion center H₂C=CH^?· were calculated.     

The energy and geometric characteristics of the transition state in reactions of RO<Stack><Subscript>2</Subscript><Superscript>•</Superscript></Stack> with carbonyl compound C-H bonds

The energy and geometry of the transition state in reactions of the ethyl peroxyl radical with ethane, ethanol (its α and β C-H bonds), acetone, butanone-2, and acetaldehyde were calculated by the density functional theory method. In all these reactions (except EtO_2/? + ethanol α C-H bond), the C…H…O reaction center has an almost linear configuration (φ = 176° ± 2°); polar interaction only influences the r ^≠ (C…O) interatomic bond. In the reaction of EtO_2/? with the ethanol α C-H bond, it is the O-H…O H-bond formed in the transition state that determines the configuration of the reaction center with the angle φ(C…H…O) = 160°. The results were used to estimate the r ^≠ (C…H) and r ^≠ (O…H) interatomic bonds in the transition state by the method of intersecting parabolas and the contribution of polar interaction to the activation energy of reactions between peroxyl radicals and aldehydes and ketones.