Unusual conformational preferences of 1,3‐dimethyl‐3‐isopropoxy‐3‐silapiperidine

The conformational analysis of the first representative of the Si‐alkoxy substituted six‐membered Si,N‐heterocycles, 1,3‐dimethyl‐3‐isopropoxy‐3‐silapiperidine, was performed by low‐temperature ¹H and ¹³C NMR spectroscopy and DFT theoretical calculations. In contrast to the expectations from the conformational energies of methyl and alkoxy substituents, the Me_axi‐PrO_eq conformer was found to predominate in the conformational equilibrium in the ratio Me_axi‐PrO_eq : Me_eqi‐PrO_ax of ca. 2 : 1 as from the ¹H and ¹³C NMR study. The thermodynamic parameters obtained by the complete line shape analysis showed that the main contribution to the barrier to ring inversion originates from the entropy term of the free energy of activation. Copyright © 2012 John Wiley & Sons, Ltd.     

A resonance Raman spectroscopic study of the protonation of Disperse Orange 25 in solution and adsorbed on oxide surfaces

The protonation of Disperse Orange 25 (DO25) in aqueous solution, and upon adsorption on oxide surfaces, was studied by resonance Raman (RR) spectroscopy. The neutral and protonated forms of DO25 were modelled by DFT calculations of the isolated molecules in the gas phase at the B3‐LYP/DZ level, enabling calculation of the vibrational spectra of these species, together with vibrational assignments. RR spectra show that DO25 is physisorbed on the SiO₂ surface, but its adsorption on SiO₂ Al₂O₃ or H‐mordenite results in protonation. This observation indicates the presence of Brønsted acidic sites on these oxide surfaces with pK_a values ⩽2.5. RR studies of the adsorption of DO25 can therefore provide useful information on the nature of surface acidity on oxides, which is complementary to that obtained from other probe molecules. Copyright © 2007 John Wiley & Sons, Ltd.     

Effect of boron and nitrogen co-doping on CNT's electrical properties: Density functional theory

In this work, we have theoretically studied the changes in electrical properties of three different geometrical structures of carbon nanotubes upon co-doping them with boron and nitrogen atoms. We applied different doping mechanisms to study band structure variations in the doped structures. Doping carbon nanotubes with different atoms will create new band levels in the band structure and as a consequence, a shift in the Fermi level occurs. Whereas, filling up the lowest conduction/ upper valence bands created an up/ downshift in the Fermi level. Moreover, dopants concentration and dopants position play a critical rule in defining the number of new band levels. These new band levels in the band gap region represented as new peaks appeared in the density of states. These new bands are solely attributed to co-doping carbon nanotubes with boron and nitrogen atoms.     

Synthesis,spectroscopic and structural characterisation of two p-nitrobenzamide compounds: experimental and DFT study

The title molecules, N-(1,5-dimethyl-3-oxo-2-phenyl-1H-3-(2H)-pyrazolyl)4-nitrobenzamide (C₁₈H₁₆N₄O₄·H₂O) (I) and 2,2-dimethyl-3-(4-nitrobenzoyl)-5-(phenylamino)-2,3-dihydro-1,3,4-thiyadiazole (C₁₇H₁₆N₄O₃S) (II), were prepared and characterised by ¹H NMR, ¹³C NMR, infrared spectroscopy (IR) and structural X-ray diffraction (XRD) techniques. The molecular geometries, vibrational frequencies of the title compounds in the ground state have been calculated by using the density functional theory (DFT) method with 6-31G(d) basis set, and compared with the experimental data. The calculated results showed that the optimised geometries from the DFT method agree with the X-ray structures well for both compounds. Theoretical calculations of harmonic vibration frequencies are in good agreement with experimental results. To determine conformational flexibility, the molecular energy profiles of the title compounds were obtained. Besides, molecular electrostatic potential (MEP), frontier molecular orbitals (FMO) analysis and thermodynamic properties of the title compounds were investigated by theoretical calculations.     

Density functional theory calculations and vibrational spectra of p‐bromonitrobenzene

FT‐IR and FT‐Raman spectra of p‐bromonitrobenzene (p‐BNB) have been recorded in the region 4000–400 cm⁻¹ and 4000–50 cm⁻¹, respectively. The molecular structure, geometry optimization, vibrational wavenumbers have been investigated. The spectra were interpreted with the aid of normal coordinate analysis based on the density functional theory (DFT) using the standard B3LYP/6‐31G method and basis set combination and was scaled using multiple scale factors yielding good agreement between observed and calculated wavenumbers. The results of the calculations are applied to simulate infrared and Raman spectra of the title compound which showed reasonable agreement with the observed spectra. Copyright © 2009 John Wiley & Sons, Ltd.     

苯乙烯化苯酚的密度泛函研究

以苯乙烯化苯酚(SP-2)为研究对象,采用密度泛函理论的M06-2X/6-311g(d,p)方法,进行了分子结构优化.在此基础上,对其分子轨道、能级、最高占据轨道(HOMO)和最低空轨道(LUMO)、红外光谱(IR)、核磁共振谱(NMR)、紫外-可见吸收光谱(UV-Vis)进行了模拟计算.根据能级和分子轨道计算结果,主要讨论了苯乙烯化苯酚的最高占据轨道(HOMO)和最低空轨道(LUMO)的特点;获得了红外光谱(IR)、核磁共振谱(NMR)、紫外-可见吸收光谱(UV-Vis)计算结果,并对谱图数据进行了分析讨论.     

Electrochemical properties and radical anions of carbocycle‐fluorinated quinoxalines and their substituted derivatives

Electrochemical reduction (ECR) and oxidation (ECO) of 5,6,7,8‐tetrafluoroquinoxaline ( 1 ) and its derivatives bearing various substituents R (7‐H ( 2 ), 7,8‐H₂ (3 ), 6‐CF₃ ( 4 ), 6‐Cl ( 5 ), 5,7‐Cl₂ ( 6 ), 5‐NH₂ ( 7 ), 6‐OCH₃ ( 8 ), 6,7‐(OCH₃)₂ ( 9 ), 6,7,8‐(OCH₃)₃ ( 10 ), 5,6,7,8‐(OCH₃)₄ ( 11 ), 6‐OCH₃,7‐N(CH₃)₂ ( 12 ), 6‐N(CH₃)₂ ( 13 ), 6,7‐(N(CH₃)₂)₂ ( 14 ), 5,6,7‐(N(CH₃)₂)₃ ( 15 ), and 7,8‐cyclo‐(=CF‐CF = CF‐CF=) ( 16 )) in the carbocycle have been studied by cyclic voltammetry in MeCN. For 1 – 4 and 7 – 15 , the first reduction peaks have been found to be 1‐electron and reversible, thus corresponding to the formation of their radical anions (RAs), which are long lived at 295 K except those of 4 – 6 and 15 , 16 . Irreversible hydrodechlorination has been observed for 5 and 6 at the first step of their ECR confirmed by EPR detection of corresponding RAs of 2 and 5,7‐H₂ derivative of 1 ( 17 ) at the next steps. Electrochemically generated RAs of 1 – 3 , 7 – 14 , and 17 have been characterized in MeCN by EPR spectroscopy together with DFT calculations at the (U)B3LYP/6‐31 + G(d) level of theory using PCM to describe the solvent. A noticeable alternation of spin density on the –NCCN– moiety of quinoxaline has been observed for all RAs possessing R‐substitution asymmetry. The comparative electron‐accepting ability of 1 – 15 has been analyzed in terms of their experimental reduction peak potentials and the (U)B3LYP/6‐31 + G(d)‐calculated gas‐phase first adiabatic electron affinities (EAs). The differences in electron transfer solvation energies for 1 – 15 have been evaluated on the basis of ECR peaks' potentials and calculated gas‐phase EAs. The ECO of 1 – 5 and 7 – 14 has been found to be irreversible.     

Theoretical and spectroscopic studies of 5‐aminoorotic acid and its new lanthanide(III) complexes

The complexes of cerium(III) and neodymium(III) were synthesized by reaction of the respective inorganic salts with 5‐aminoorotic acid (H₄L) in amounts equal to the metal:ligand molar ratio of 1:3. The structures of the final complexes were determined by means of spectral (IR, Raman, ¹H NMR and ¹³C NMR) and elemental analysis. Significant differences in the IR spectra of the complexes were observed as compared to the spectrum of the ligand. A comparative analysis of the Raman spectra of the complexes with that of the free H₄L allowed a straightforward assignment of the vibrations of the ligand groups involved in coordination. The geometry of H₄L was computed and optimized for the first time with the Gaussian03 program using the B3PW91/6‐311++G**, B3PW91/LANL2DZ, B3LYP/6‐311++G** and B3LYP/LANL2DZ methods. The experimental IR and Raman bands of the ligand were assigned to normal modes on the basis of DFT calculations. The vibrational analysis performed for the studied species, H₄L and its complexes, helped to explain the vibrational behavior of the ligand vibrational modes sensitive to interaction with the lanthanides. The vibrational study gave evidence for the coordination mode of the ligand to lanthanide ions and was in agreement with the other theoretical prediction. Copyright © 2006 John Wiley & Sons, Ltd.     

Novel pyridyl‐substituted coumarin and its perchlorate salt–crystal structure and spectroscopic properties

The novel pyridyl‐substituted coumarin ( 1 ) and its perchlorate salt ( 2 ) have been synthesized and their structure and properties elucidated in detail spectroscopically, thermally and structurally, using single crystal X‐ray diffraction for 2 , linear‐polarized solid state IR‐spectroscopy, UV‐spectroscopy, TGA, DSC, DTA, and positive and negative ESI MS. Quantum chemical calculations were used to obtain the electronic structure, vibrational data and electronic spectra. The studied compound crystallizes in the centrosymmetric space group P‐1 and exhibits an infinite layered structure with the ions linked by means of the intermolecular N⁺H…OClO₃ (2.795 Å) interactions. The cations are disposed in a manner leading to a significant π‐stacking effect with a distance of 2.980 Å. The effects of N_py protonation on the optical and magnetic properties are elucidated by comparing the data of the protonated and neutral compounds. Copyright © 2009 John Wiley & Sons, Ltd.     

Density functional slab model studies of water adsorption on flat and stepped Cu surfaces

Density functional and periodic slab model calculations are performed to study adsorption of water on various Cu surfaces, focusing on monomers and dimers at the planar Cu surfaces and monomers at stepped ones. Single water molecules tend to weakly bind to atop positions with the molecular plane basically parallel to the substrate surface on the planar surfaces or the step plane on the stepped surfaces with negligible structural deformation of water. The experimental adsorption energies of water on the (1 1 1) and (1 0 0) surfaces are about twice as large as the theoretical values of monomerically adsorbed water. This phenomenon is demonstrated to be due to formation of water clusters and/or existence of surface defects. It is revealed that the most favorable hexagonal ring superstructure on Cu(1 1 0) is a four-layer structure, not the commonly accepted bi-layer configuration. We found that the adsorption energy of monomeric water correlates linearly with following quantities, respectively: the bond length and the stretching frequency of the Cu-O bond, the coordination number of the surface Cu atom, the surface work function of the clean surface and the 1b₁ MO energy shift with respect to the value in the gas phase.     

Ring inversion process for a series of 3,5‐dialkyl‐1‐oxa‐3,5‐diazacyclohexanes: 1H DNMR study and semiempirical calculations

The ring inversion process for a series of 3,5‐dialkyl‐1‐oxa‐3,5‐diazacyclohexanes was studied using proton dynamic nuclear magnetic resonance (¹H DNMR) spectroscopy in conjunction with semiempirical calculations. At low temperature, the ring methylene protons decoalesced into two AB spin systems in a 2:1 ratio. Lineshape simulations of the DNMR spectra provided first‐order rate constants for magnetic exchange. The energy barrier for each inversion reaction was calculated from the respective rate constants. In general, as the size of the N‐alkyl group increased, the barrier to ring inversion decreased. A similar trend was seen in semiempirical calculations that modeled the ring inversion process. Copyright © 2010 John Wiley & Sons, Ltd.     

Density functional theoretical studies on photoswitching and charge migration dynamics of thio and selenoureidopeptides

Density functional theoretical calculations have been performed to investigate the changes in electronic structure at ground and excited states of ureidopeptides on substitution with higher chalcogens like sulphur and selenium for oxygen. This replacement results in a reduced preference towards the intramolecular hydrogen bonding interaction, thus linear conformers are found to be stable at both states. Nevertheless, conformational switching observed during this process is mainly due to n to π* transition that leads to the dihedral angle ω change from trans to cis with a rotational barrier of 10 to 17 kcal mol^‐1. The computed barrier is lesser than that reported for oxopeptides (20 kcal mol^‐1). And, the hole migration dynamics after immediate ionization illustrates that the hole originated at ureido end evolves in time (2?4 fs) while the hole generated at the carboxylate end will not evolve as reported for ureidopeptides. The usage of these candidates as photoswitches has also been explored.     

DFT study of the 1,3‐dipolar cycloaddition of azomethine ylides with maleimide,maleic anhydride,methylacrylate and some simple substituted alkenes

DFT calculations involving the B3LYP functional and 6‐31G(d) basis set have been performed to rationalize the reactivity, regioselectivity, enantioselectivity and diasteriofacial selectivity in the context of 1,3‐dipolar cycloaddition (13DC) reactions of a few acyclic and two cyclic azomethine ylides (AY) leading to enantiomeric/ diasteriomeric excess of the products. In particular, N‐substituted and C‐substituted AYs have been considered for reactions with the substituted ethylenes, maleimide, maleic anhydride and methyl acrylate. From an analysis of the results of calculation for the selected reactions, the regio‐ and exo/endo‐stereoselectivity have been explained. Reactions were followed through transition state (TS) structure optimization, calculation of IRC and activation energies. A rationalization of the trends in regioselectivity and enantioselectivity was attempted with the help of HOMO–LUMO energies, electrophilicity differences (Δω) and an analysis of Pauling's bond order (PBO) in the TS. Copyright © 2009 John Wiley & Sons, Ltd.     

Solid state NMR studies and chemical shift calculations of a gold(I) complex with a diphosphacyclobutadiene cobaltate sandwich anion

The ³¹P and ¹³C solid state nuclear magnetic resonance spectra of a neutral gold(I) complex with bis(diphosphacyclobutadiene) cobaltate anions, [Au{Co(P₂C₂tPent₂)₂}₂(PMe₃)₂], are reported. Complete ³¹P resonance assignments have been derived from saturation transfer, radio-frequency driven recoupling (RFDR) and RTOBSY experiments and confirmed further by ab-initio calculations of magnetic shielding tensors by density functional theory, with consideration of relativistic effects. Coordination of the diphosphacyclobutadiene ring with gold(I) results in a high-frequency shift of the ³¹P signal of the directly coordinated P atom, whereas a low-frequency shift is observed for the P atom at the opposite end of that ring. Based on these results, a previous assignment made for the complex salts [Au(PMe₃)₄][Au{Co(P₂C₂Ad₂)₂}₂] and [K(18-crown-6)(thf)₂][Au{Co(P₂C₂Ad₂)₂}₂] (Ad=adamantyl) must be corrected.     

Experimental (UV,NMR, IR and Raman) and theoretical spectroscopic properties of 2-chloro-6-methylaniline

In this work, the experimental and theoretical UV, NMR and vibrational spectra of 2-chloro-6-methylaniline (2-Cl-6-MA, C₇H₈NCl) were studied. The ultraviolet absorption spectra of compound that dissolved in ethanol were examined in the range of 200–400 nm. The ¹H, ¹³C and DEPT NMR spectra of the compound were recorded. FT-IR and FT-Raman spectra of 2-Cl-6-MA in the liquid phase were recorded in the region 4000–400 cm^?1 and 3500–50 cm^?1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated using density functional theory (DFT) employing B3LYP exchange correlation and the 6-311++G(d,p) basis set. The vibrational frequencies were calculated and scaled values were compared with experimental FT-IR and FT-Raman spectra. The observed and calculated frequencies were found to be in good agreement. The complete assignments were performed on the basis of the total energy distribution (TED) of the vibrational modes, calculated with scaled quantum mechanics (SQM) method. Isotropic chemical shifts were calculated using the gauge-invariant atomic orbital (GIAO) method. Comparison of the calculated NMR chemical shifts and absorption wavelengths with the experimental values revealed that DFT method produces good results.     

Time‐resolved spectroscopic and density functional theory investigation of the photochemistry of suprofen

The photochemistry of suprofen (SPF) was investigated by femtosecond transient absorption (fs‐TA), resonance Raman (RR) and nanosecond time‐resolved resonance Raman (ns‐TR³) spectroscopic methods to gain additional information so as to better elucidate the possible photochemical reaction mechanism of suprofen in several different solvents. In neat acetonitrile (MeCN), the fs‐TA and ns‐TR³ experimental data indicated that the lowest lying excited singlet state S₁ (nπ*) underwent an efficient intersystem crossing process (ISC) to the excited triplet state T₃ (ππ*), followed by an internal conversion (IC) process to T₁ (ππ*). In the aqueous solution, a triplet biradical species (³ETK‐1) was obtained as the product of a decarboxylation process from triplet suprofen anion (³SPF⁻) and the reaction rate of the decarboxylation process was determined by the concentration of H₂O. A protonation process for ³ETK‐1 leads to formation of a neutral species (³ETK‐3) that was directly observed by ns‐TR³ spectra, then this ³ETK‐3 species decayed via ISC process to generate final product. Copyright © 2014 John Wiley & Sons, Ltd.     

Vibrational and computational analysis for molecular structure properties of N-(2-(trifluoromethyl)phenyl)acetamide: Density functional theory approach

Abstract

The conformational study using Potential Energy Surface analysis was performed and its minimum energy conformer has been obtained for N-(2-(Trifluoromethyl)phenyl)acetamide. Fourier Transform Infrared and Fourier Transform Raman investigation have been done experimentally and theoretically. Nuclear Magnetic Resonance analysis has been performed to obtain ¹H and ¹ Bassetto, M.; Ferla, S.; Pertusati, F. Polyfluorinated Groups in Medicinal Chemistry. Future Med. Chem. 2015, 7, 527–546.[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]C chemical shifts. Ultraviolet-Visible analysis has been performed to obtain maximum absorption wavelength. The molecular orbital diagram with different energies has been obtained and compared with the band gap of Ultraviolet-Visible data. Wave function analysis has been discussed to know the electronic properties. Thus, this present study reports the structural, electrical, chemical activities of the title compound.     

Synthesis and electrochemical evaluation of 2‐substituted imidazolium salts

Herein, we report the synthesis, electrochemical, and computational evaluation of six 2‐substituted imidazolium bromides and six 2‐substituted imidazolium triflates. All final compounds were obtained in 2 or fewer synthetic steps from inexpensive starting materials and display a single, irreversible electrochemical reduction. The reduction potentials span a range greater than 1 V depending on the electron withdrawing power of the 2‐substituent. Imidazolium bromides such as Bn₂(H)ImBr reduce with E_1/2 = ?2.70 V vs Fc/Fc⁺, whereas the electron‐withdrawing Br‐containing analog Bn₂(Br)ImBr reduces at only ?1.58 V vs Fc/Fc⁺. The reduction potential of imidazolium bromides obeys a linear free energy relationship to σ_m Hammett constants, whereas imidazolium triflates correlate better with the σ_p Hammett constants. These results indicate that the stabilizing effect of the 2‐substituent is anion‐sensitive, changing from induction to resonance upon exchanging bromide for triflate. Predicted electron affinities from density functional theory–optimized structures of imidazolium cations and reduced species more closely match experimental data for the triflates, suggesting that a triflate anion does not electronically perturb the imidazolium core as much as a bromide. Taken together, these data highlight the dual modularity of imidazolium salts by changing both 2‐substituent and anion.     

密度泛函理论研究硫族元素取代对单层Ag2S结构和电子性质的影响

本文利用第一性原理计算讨论了硫族元素掺杂单层Ag₂S的缺陷形成能和电子性质.缺陷形成能反映了在富Ag条件下的掺杂更容易.计算得到的带隙、Mulliken布居和态密度展示出了其相应结构的电子性质.与纯单层的Ag₂S相比,Se/Te掺杂Ag₂S后的带隙显示出其电导率变化不大.基于Mulliken原子和键布居,研究了硫族元素掺杂后Ag₂S中的共价性.此外,通过讨论态密度,分析了能级的移动和电子的贡献.     

硝酸丙酯结构、振动频率和热力学性质的密度泛函理论研究

用密度泛函理论(DFT)研究硝酸丙酯化合物的分子结构、振动光谱和热力学等基本性质.取BLYP、B3LYP方法和6-31G*、6-31G**、6-311G*、6-311G**基组,对硝酸丙酯分子的几何构型进行全优化计算并分析其电子结构性质.和考虑了二级相关能校正的MP2/6-311G*计算结果比较表明,B3LYP/6-31G*是研究许多较大体系化合物卓有成效和颇有前途的方法.在B3LYP/6-31G*的水平上对优化后的结构进行了正则振动频率分析,用因子0.95校正后的振动光谱和实验结果比较,符合较好.进一步