Conformational analysis of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinone derivatives by the density functional method and IR spectroscopy

We have used the PBE/3z, B3LYP/6-31G, B3LYP/6-31G(d), and B3LYP/6-311G(d) methods to study the conformational mobility of 2,3-dihydro-3-O-(1,4-naphthoquinon-2-yl)-2-oxo-1,4-naphthoquinones (1–4). We have shown that more than 99% of these compounds exist as the major tautomeric form, while differences in the structure of the Q_2H (2,3-dihydro-2-oxo-1,4-naphthoquinones) and Q_1,4 (1,4-naphthoquinon-2-yl) moieties lead to qualitative differences in the internal rotation potentials of the ethyl substituents V(θ_Et−1) and V(θ_Et−2), and consequently each of compounds 1−4 exists as six different rotameric forms. For diquinone 3, we have calculated the dependences of the frequencies (ν) and intensities (A) of the normal vibrations on the torsional angles θ_Et−1 and θ_Et−2, and also on the changes in the geometry of the ether bond. We have found that the values of ν and A for the bands in the carbonyl region of the IR spectrum change little on going from one rotameric form to another, and also for the in-plane bends of the ether bond, and change considerably for the out-of-plane bends of the ether bond. However, for T ≤ 300 K, there is no qualitative change in the overall contour, and it can be interpreted based on a simple additive model. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 5, pp. 573–581, September–October, 2006.     

SeOx(x=1,2)的从头算势能曲线和光谱常数

采用从头算的多种方法和基组优化计算SeO_x(x=1,2)自由基的基态结构、谐振频率及离解能,优选出QCISD(T)/6-311+G(2df)、B3LYP/6-311G(3d2f)方法分别对SeO、SeO₂自由基进行计算,计算结果与实验结果吻合很好.对SeO自由基拟合出Murrell-Sorbie势能函数参数,计算出SeO自由基的光谱常数和力常数.计算出SeO₂自由基力常数,导出SeO₂自由基的多体展式势能函数,发现SeO₂自由基对称伸缩振动势能图中在对称的O+SeO→SeO₂反应通道上有一鞍点,其活化能约为48.24 kJ·mol^-1,O原子需要越过0.5 eV的能垒才能生成SeO₂的稳定结构.     

Synthesis of dialkyl 2,5-dihydro-5-oxo-1,2-azaphosphole-3,4-dicarboxylates

The adducts produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates were trapped by arylsulfonyl isocyanates to produce dialkyl 2,5-dihydro-5-oxo-1,2-azaphosphole-3,4-dicarboxylates in good yields.     

Mass Spectral Fragmentation Patterns of Some Substituted 10,Ll-Dihydro-5H-Dibenzo[A,D] Cycloheptene-5-One and 9,10-Dihydro-4H-Benzo [4,5]Cyclohepta[1,2-B]Thiophene-4-One

Electron impact mass spectra of some substituted 10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5-one and 9,10-dihydro-4H-benzo[4,5] cyclohepta[1,2-b] thiophene-4-one have been recorded and the identity of various ions in the mass spectra established. Substituted dibenzosuberones (2-6) exhibit one main fragmentation route, which include the elimination of the tropolone molecule from the dibenzosuberone fragment cation. Their monothiophene analogues(7-11) exhibit characteristic CO elimination from the molecular ion and formation of corresponding naphtho[1,2-b]thiophene radical cation which after elimination of CS or HCS from the thiophene nuclei give rise to the benzotrophyne radical cation.     

Theoretical study of the [Si,C, P,O] potential energy surface

The structures, energetics, spectroscopies and stability of the doublet [Si, C, P, O] radical are explored at the density functional theory and ab initio levels. Eighteen isomers connected by 22 interconversion transition states are located at the DFT/B3LYP/6-311G(d) level. The structures of the kinetically stable isomers and the relevant transition states are further optimized at the QCISD/6-311G(d) level followed by CCSD(T)/6-311 + G(2df) single-point energy calculations. At the QCISD/6-311G(d) level, the lowest-lying isomer is the cyclic O-cCSiP 8 (0.0 kcal/mol) with considerable kinetic stability of 22.0 kcal/mol. In addition, two bent isomers OSiCP 1 (7.3 kcal/mol) and SiCPO 3 (34.7 kcal/mol) also possess considerable kinetic stability (more than 10.0 kcal/mol). As a result, three isomers 1, 3 and 8 are predicted to be possible candidates for future experimental and astrophysical detection. The bonding nature of the three isomers is analysed. The calculated results are compared with those of the analogous radical [Si, C, N, O]. Implications in the laboratory and interstellar space are also discussed. The predicted structures and spectroscopic properties are expected to be informative for the identification of [Si, C, P, O] in the laboratory and space.     

PCl_X(X=1,2)分子基态的结构与势能函数

采用单双取代的二次组态相互作用( QCISD)方法,使用多种基组对PClx (X=1,2)分子基态结构进行优化计算,选出最优基组6-311+ G(df)和6-311G(df)分别对PCl和PCl2分子的离解能、谐振频率和力常数等进行计算,结果与实验值符合很好.在此基础上推导出PCl2分子基态的多体展式势能函数,其等值势能图正确反应了PCl2分子的结构特征及势阱深度,进一步讨论Cl+ PCl和P+ClCl分子反应的势能面特征.这些结果可用于微观反应动力学的研究.     

Theoretical and antimicrobial activity study for ethyl{4-[3-(1H-imidazole-1-yl)propyl]-3-methyl-5-oxo-4,5-dihydro-1H-1,2,4-triazol-1-yl}acetate

Ethyl{4-[3-(1H-imidazole-1-yl)propyl]-3-methyl-5-oxo-4,5-dihydro-1H-1,2,4-triazol-1-yl}-acetate (I) was synthesized as described in the literature and studied by proton and carbon-13 nuclear magnetic resonance, Fourier transform infrared spectroscopic techniques. Theoretical calculations were performed by the density functional method with 6-311G(d,p) and 6-311++G(d,p) basis sets. Structural parameters of compound I, vibrational frequencies, and chemical shift values were determined. The antimicrobial activity of compound I was tested for seven standard bacteria; Staphylococcus aureus, Escherichia coli, Salmonella typhimurium, Yersinia enterocolitica, Listeria monocytogenes, Shigella flexneri, Pseudomonas aeruginosa, and one standard fungi isolate by microdilution broth assay with Alamar Blue Dye. The in vitro results show that compound I has antimicrobial activity against to two standard bacteria, Shigella flexneri and Listeria monocytogenes. And also, the antifungal activity was not detected against selected fungi isolate, Candida tropicalis.     

Theoretical investigation of the oxidation pathways of the Cl-initiated reaction of 2-methyl-3-buten-2-ol

The mechanism and products of the reaction of 2-methyl-3-buten-2-ol (MBO232) with Cl atoms in the presence of O₂ have been elucidated by performing high-level quantum chemistry calculations. The geometries of the reactants, intermediates, transition states, and products are optimized at the MP2(full)/6-311G(d,?p) level, and their single-point energies are refined at the CCSD(T)/6-311?+?G(d,?p) level. The potential energy surface profiles have been constructed at the CCSD(T)/6-311?+?G(d,?p)//MP2(full)/6-311G(d,?p)?+?0.95?×?ZPE level of theory, and the possible channels involved in the reaction are also discussed. The calculations indicate that the reaction predominantly proceeds via the addition of Cl atoms to the double bond rather than the direct abstraction of the H atoms in MBO232. The nascent adducts (CH₃)₂C(OH)CHCH₂Cl (IM1) and (CH₃)₂C(OH)CHClCH₂ (IM2) do not undergo subsequent isomerization and dissociation reactions, but rather react with O₂. The theoretical results show that the major products are CH₂ClCHO and CH₃C(O)CH₃ for the reaction of MBO232?+?Cl in the presence of O₂, which is in good agreement with the experimental finding.     

Theoretical investigation on structures,stability and properties of [P,X, Y] (X=C,Si; Y = O,S) isomers

The structures, energetics and stability of the [P, X, Y] (X?=?C, Si; Y?=?O, S) radicals are explored by means of the density functional theory and ab initio levels. Seventeen [P, X, Y] isomers and 14 interconversion transition states are obtained at the B3LYP/6-311G(d) level. At the CCSD(T)/6-311?+?G(2df)//QCISD/6-311G(d)?+?ZPVE level, the lowest-lying isomers are the linear PCO 1a (0.0?kcal/mol), PCS 1b (0.0) and the three-membered ring cPSiO 1c (0.0), cPSiS 1d (0.0) on their respective potential energy surfaces. These four isomers exhibit considerably not only thermodynamic but also kinetic stabilities. Additionally, the cyclic cPCS 2b (32.8) and linear PSiS 2d (18.6) possess also high kinetic stability. All of six isomers 1a, 1b, 2b, 1c, 1d and 2d are considerably stabilized by a barrier of at least 20?kcal/mol, and may be detected in the laboratory or interstellar space. Their valence bond structures and possible formation strategies in the laboratory and space are discussed in detail. Finally, the similarities and discrepancies on structures and stabilities between [P, X, Y] (X?=?C, Si; Y?=?O, S) isomers are compared. These predicted results are highly expected to be informative for the future identification of [P, X, Y] (X?=?C, Si; Y?=?O, S) in the laboratory and space.     

UV‐induced transformations of matrix‐isolated 1,3,4‐thiadiazole‐2‐thiones

Monomers of 5‐mercapto‐1,3,4‐thiadiazole‐2‐thione (bismuthiol) were studied using an experimental matrix‐isolation technique as well as by carrying out theoretical quantum chemical calculations. The calculations, performed using the quadratic configuration interaction method with single and double excitations (QCISD)/6‐31++G(d,p)//DFT(B3LYP)/6‐311++G(2d,p), predict that the thione–thiol tautomer of bismuthiol should be significantly (by more than 19 kJ mol^?1) more stable than other tautomeric forms. Accordingly, only the signatures of the thione–thiol tautomer were observed in the FT‐IR spectrum of bismuthiol, recorded directly after deposition of an Ar matrix. UV (λ > 320 nm) irradiation induced the conversion of the thione–thiol tautomer into the dithiol form. Analogous investigations were carried out for two related compounds: 5‐methyl‐1,3,4‐thiadiazole‐2‐thione and 5‐methylthio‐1,3,4‐thiadiazole‐2‐thione. For these two species, only the thione tautomeric forms were observed after deposition of Ar matrices. These tautomers were predicted (by QCISD calculations) to be more stable (by at least 19 kJ mol^?1) than other tautomeric forms. Upon UV irradiation, the most stable thione forms of these compounds were transformed into the corresponding thiol tautomers. Direct observation of the thione → thiol phototautomeric processes provides a clear proof that intramolecular proton transfer reaction can occur in molecules, such as bismuthiol, in spite of the increased NH···S distance, in comparison to other phototautomerizing species studied so far. All the isomers of the studied compounds (substrates and products of the photoreactions) were identified by comparison of their IR spectra with the spectra calculated at the DFT(B3LYP)/6‐311++G(2d,p) level of theory for possible isomeric structures. Copyright © 2009 John Wiley & Sons, Ltd.     

DFT study on abstraction reaction mechanism of oh radical with 2‐methoxyphenol

Reaction mechanism of 2‐methoxyphenol (2MP) (guaiacol) with OH radical has been performed using density functional theory methods BH&HLYP and MPW1K method with 6‐311++G(d,p) basis set. Single‐point energy calculations were done using CCSD(T)/6‐311++G(d,p). The theoretical results reveal that the hydrogen abstraction from methoxy group is found to be the dominant reaction channel with an energy barrier of 9.31 kcal/mol. Also, time‐dependent density functional theory calculations have been performed using BH&HLYP/6‐311++G(d,p) level of theory, and the results reveal that the reactions occur in ground state than the excited state. The results of reaction force profile indicate that structural rearrangements are most influential with high percentage than the relaxation process. The calculated theoretical rate constants (12.19 × 10^?11 cm³ molecule^?1 s^?1) are in good agreement with the experimental rate constant. The atmospheric lifetime of 2‐methoxyphenol with respect to OH radicals is 2.27 hours, which implies that OH radical plays an important role in the degradation of 2MP. The Wiberg bond index of the abstraction reaction reveals that the bond order is concerted, partially synchronic. The reactant‐like transition state satisfies Hammond postulate, which eventually results in an exothermic reaction, and the product‐like transition state reveals in endothermic nature.     

The catalytic effects of H2CO3, CH3COOH,HCOOH and H2O on the addition reaction of CH2OO + H2O → CH2(OH)OOH

The addition reaction of CH₂OO + H₂O → CH₂(OH)OOH without and with X (X = H₂CO₃, CH₃COOH and HCOOH) and H₂O was studied at CCSD(T)/6-311+ G(3df,2dp)//B3LYP/6-311+G(2d,2p) level of theory. Our results show that X can catalyse CH₂OO + H₂O → CH₂(OH)OOH reaction both by increasing the number of rings, and by adding the size of the ring in which ring enlargement by COOH moiety of X inserting into CH₂OO···H₂O is favourable one. Water-assisted CH₂OO + H₂O → CH₂(OH)OOH can occur by H₂O moiety of (H₂O)₂ or the whole (H₂O)₂ forming cyclic structure with CH₂OO, where the latter form is more favourable. Because the concentration of H₂CO₃ is unknown, the influence of CH₃COOH, HCOOH and H₂O were calculated within 0–30 km altitude of the Earth's atmosphere. The results calculated within 0–5 km altitude show that H₂O and HCOOH have obvious effect on enhancing the rate with the enhancement factors are, respectively, 62.47%–77.26% and 0.04%–1.76%. Within 5–30 km altitude, HCOOH has obvious effect on enhancing the title rate with the enhancement factor of 2.69%–98.28%. However, compared with the reaction of CH₂OO + HCOOH, the rate of CH₂OO···H₂O + HCOOH is much slower.     

Theoretical study of the CH3 + NS and related reactions: mechanism of HCN formation

More than thirty equilibrium and transition structures on the [CH₃NS] potential energy surface have been located using the B3LYP/6-311 + + G(d,p) method. Thioformaldoxime (3) turns out to be the most stable isomer followed by thionitrone (2), a three-membered ring, thionitrosyl methane (1) and thiazyl methane. These isomers are connected to each other by 1,2H and 1,3H shifts and ring—chain rearrangement, but the associated energy barriers are rather high, making most of them stable with respect to unimolecular transformations. Starting from CH₃ + NS, a possible initial atmospheric reaction, HCN formation appears to be the most favoured process through a cascade involvement of 1, 2 and 3. The standard heats of formation, ΔH ⁰ _f,298 are calculated to be: 3, 149kJmol^?1; and 1, 218kJmol^?1; using the CCSD(T)/6-311+ +G(3df,2p) method, with an error of ±10kJ mol^?1.     

Theoretical study of B3O radical isomers and their interconversion pathways

Despite the fact that B₃O is the second simplest B _n O radical after BO, a controversy recently emerged concerning the molecular structure of its global minimum. Two recent theoretical groups predicted the linear quartet BBBO to be the ground isomer. By contrast, another recent theoretical group reported that B₃O has a doublet B₃-ring ground structure. Moreover, larger B _n O clusters usually have low-lying B₃-ring isomers. In order to determine the accurate energetic competition between linear and cyclic structures in both the doublet and quartet, and to understand the detailed isomerism between various isomers, which is vital for understanding the formation mechanism of B₃O, we report the first potential energy surface (PES) study of B₃O at various computational levels, including CCSD(T)/6-311+G(2df), CCSD(T)/aug-cc-pVTZ, CCSD(T)/aug-cc-pVQZ and G3B3 for the single-point energy, as well as B3LYP/6-311+G(d) and QCISD/6-311+G(d) for geometrical optimisation. It is shown that the isomers in the quartet state are all thermodynamically more stable than the corresponding doublet ones, and on both the quartet and doublet PESs, the linear form has the lowest energy. Therefore, our study on both linear and cyclic isomers shows that the linear quartet BBBO ⁴ 01 is definitively the ground isomer. Although being much less stable than the quartet linear BBBO global minimum by >20 kcal mol^?1, five cyclic isomers exist as local minima, with the bi-cyclic structure ⁴ 02 possessing the smallest barrier of around 15 kcal mol^?1. The dissociation energies for direct combination processes B₃ + O, B₂ + BO and B + B₂O are discussed. The present work may be helpful in obtaining a deep understanding of the doping and oxidation process of pure B _n clusters.     

A Theoretical Study of the Electronic Spectrum of Photochromic 1,2-Dihydroquinoline

Abstract

Recently, Kolc and Becker¹ reported photochromism of 1,2-dihydro quinoline. The primary act of this reaction appears to be a dissociation of the C – N sigma bond as a result of π→π? excitation which leads to a fully conjugated molecule absorbing in the visible region. This coloured form can be eradicated thermally and the whole process can be repeated. A detailed explanation of this photochromic process obviously requires a good knowledge of the electronic states and structure of the considered molecule. A theoretical study thus appeared quite useful.     

Theoretical and Experimental NMR Study of a Series of Five Nitrobenzene-1,2-Diamines

¹H-, ¹³C-, and ¹⁵N-NMR studies of five nitrobenzene-1,2-diamines in solution and solid state have been achieved and the experimental chemical shifts and coupling constants agree with the theoretical values obtained at the B3LYP/6-311 + +G(dp) computational level using the geometries fully optimized with the hybrid HF/DFT B3LYP method and the 6-31G(d) basis set. The GIAO approximation has been used to calculate the absolute shieldings. The contribution of the substituents to the ¹⁵N chemical shifts of the amino groups could be quantified using a presence/absence matrix and a multiple regression.     

Quantum chemical study of the (Z)-2-penten-1-ol (HOCH2–CH = CHCH2CH3) + OH + O2 reactions

ABSTRACT

The mechanism and products of the reaction of (Z)-2-penten-1-ol [(Z)-PO21] with OH radical in the presence of O₂ have been elucidated by using high-level quantum chemical methods CCSD(T)/6-311+G(d,p)//BH&;HLYP/6-311++G(d,p). The calculations clearly indicate that addition channels contribute maximum to the total reaction and H-abstraction channels can be neglected at temperatures of 220–500 K. The rate constant for the reaction of OH radical with (Z)-PO21 at 298 K is computed to be 1.22 × 10^?10 cm³ molecule^?1 s^?1, which is in stronger agreement with the previously reported experimental values. The kinetic data obtained over the temperature range 220?500 K are used to derive an non-Arrhenius expression: k = 3.69 × 10^?13 × exp(1763.7/T) cm³ molecule^?1 s^?1. For the reaction of (Z)-PO21with OH radical in the presence of O₂, the major primary reaction products found in this study are propanal [CH₃CH₂C(O)H] and glycolaldehyde [HOCH₂C(O)H], whereas formaldehyde [HC(O)H], 2-hydroxybutanal [CH₃CH₂CH(OH)C(O)H] and the epoxide P18 are anticipated to be minor products. The calculated results are consistent with the recent experimental observations.     

Calculation of accurate imaginary frequencies and tunnelling coefficients for hydrogen abstraction reactions using IRCmax

The effect of level of theory on the imaginary frequency and corresponding tunnelling coefficients has been studied for a test set of hydrogen abstraction reactions: ?CH₂X + CH₃Y → CH₃X + ?CH₂Y for (X,Y) = (H,H), (H,CN), (H,F), (H,Li) and (F,Li). It is found that the imaginary frequency is very sensitive to the level of theory used, with Hartree-Fock (HF) methods severely overestimating the imaginary frequency compared with high-level CCSD(T)/6-311G(d,p) calculations. The errors for the other methods are smaller but nonetheless significant, with MP2 methods overestimating the imaginary frequency and density functional theory (DFT) methods underestimating it. In the case of the HF methods, this leads to errors in the tunnelling coefficient of several orders of magnitude, while for the better DFT and MP2 methods errors of a factor of 2–3 are observed. To address this problem, an IRCmax procedure for estimating the imaginary frequency has been developed and it is found that IRCmax imaginary frequencies calculated with CCSD(T)/6-311G(d,p) single points along a low-level HF/6-31G(d) minimum energy path provide excellent approximations to the high-level values, at a fraction of the computational cost.     

POX(X=1,2)的光谱常数与从头算势能曲线

采用从头算的多种方法对PO、PO₂自由基的基态结构进行优化计算，结果表明：使用密度泛函（DFT）方法计算的结果最接近实验值.对PO双原子分子优选6-311G（3df）基组进行计算、扫描并拟合.对PO₂三原子分子优选出6-311+G（3df）方法计算结构参数、谐振频率、离解能及力常数，借助多体项展式理论导出PO₂自由基的势能函数并绘制等值势能图.发现：PO₂自由基的对称伸缩振动和旋转势能图中，在O+PO→OPO反应通道上都有鞍点出现，O原子需要越过0.55 eV的能量才能生成稳定的PO₂自由基.要形成PO₂自由基只能通过两等价的通道越过势垒才能形成.