Ab Initio RHF Research Articles

Mechanism of initiation of ethylene cationic polymerization in the presence of an aluminum chloride aquacomplex in heptane with a stoichiometric composition of 1:1:1:2 at the quantum level

In this paper, the mechanism of ethylene initiation in the presence of an aluminum chloride – water catalyst in a heptane solvent of stoichiometric composition 1:1:1:2 was studied using the ab initio RHF theoretical quantum chemical method. The activation energy and thermal effect of this reaction were obtained. These data can be useful for further research in the field of cationic polymerization, and can also be used in the development of new technological processes of polyethylene with specified physicochemical properties characteristic of fiber optics.

Metal modulated effects on the optoelectronic and charge transport properties of some graphene nanoribbons

In this study, we have investigated the effects of adding a metal on the nonlinear, mechanical and charge transport properties of some small organic graphene nanoribons (GNRs) molecule. A theoretical investigation is done using the ab initio (rhf) and DFT (B3LYP and BPBE) methods with the 6-31+g(d,p) basis set integrated in Gaussian 09. Results reveals that the metalated GNRs have higher nonlinear optical activity than the virgin counterpart. Interestingly these GNRs metal derivatives also have remarkable nonlinear optical effect in comparison to the classical push–pull organic crystal; para-nitroaniline and urea. Other remarkable results show that as compared to the starting GNRs the metalated counterparts are excellent ambipolar charge transport carriers better than the prototypic electron transport Alq3 (tris(8-hydroxyquinolinato)aluminum(III), and hole tranport TPD (N,N0-diphenyl-N,N0-bis(3-methlphenyl)-(1,10-biphenyl)-4,40-diamine. However, the metal derivative have diminished mechanical stability than the starting molecule. Metalated GNRs could therefore serve as potential candidates for the fabrication of optoelectronic and photonic devices for second and third-order NLO application.

The Creation of C13H20BeLi2SeSi. The Proposal of a Bio- Inorganic Molecule, Using Ab Initio Methods for The Genesis of a Nano Membrane

The work is an evolution of research already begin and in development. Therefore, we can observe a part that has already been commented that presents the whole development of the research from its beginning. Preliminary bibliographic studies did not reveal any works with characteristics studied here. With this arrangement of atoms and employees with such goals. Going beyond with imagination using quantum chemistry in calculations to obtain probable one new bio-inorganic molecule, to the Genesis of a bioinorganic membrane with a combination of the elements Be, Li, Se, Si, C and H. After calculation a bio-inorganic seed molecule from the previous combination, it led to the search for a molecule that could carry the structure of a membrane. From simple molecular dynamics, through classical calculations, the structure of the molecule was stabilized. An advanced study of quantum chemistry using ab initio, HF (Hartree-Fock) method in various basis is applied and the expectation of the stabilization of the Genesis of this bio-inorganic was promising. The calculations made so far admit a seed molecule at this stage of the quantum calculations of the arrangement of the elements we have chosen, obtaining a highly reactive molecule with the shape polar-apolar-polar. Calculations obtained in the ab initio RHF method, on the set of bases used, indicate that the simulated molecule, C13H20BeLi2 SeSi, is acceptable by quantum chemistry. Its structure has polarity at its ends, having the characteristic polar-apolar-polar. Even using a simple base set the polar-apolar-polar characteristic is predominant. The set of bases used that have the best compatible, more precise results are CC-pVTZ and 6-311G (3df, 3pd). In the CC-pVTZ base set, the charge density in relation to 6-311G (3df, 3pd) is 50% lower. The structure of the bio-inorganic seed molecule for a bio-membrane genesis that challenge the current concepts of a protective mantle structure of a cell such as bio-membrane to date is promising, challenging. Leaving to the biochemists their experimental synthesis.

The Pyranoside-into-Furanoside Rearrangement of Alkyl Glycosides: Scope and Limitations

The pyranoside-into-furanoside (PIF) rearrangement was recently reported as a useful tool for the synthesis of furanoside-containing complex oligosaccharides. Until now, this transformation has only been described for some protected allyl-β- d -galactosides and one l -fucoside. In this communication its applicability is expanded. The formation of furanosides was observed under acid-promoted sulfation for a series of galactosides with varying alkyl substituents at the anomeric position as well as for several fucosides and glucosides. Meanwhile, furanoside formation was not detected in the case of mannopyranosides. The different reactivity of substrates was explained by values of activation barriers of endocyclic C1–O5 bond cleavage calculated by ab initio RHF methods. The reported results clarify the scope and limitations of the PIF rearrangement, which is important for its application in the synthesis of carbohydrate structures of practical meaning.

Quantum-chemical and NMR study of nitrofuroxanoquinoline cycloaddition

Using DFT/B3LYP and ab initio RHF quantum-chemical calculations in the triple-zeta basis set 6-31++G** the endo and exo cycloaddition mechanism for the interaction of ethyl vinyl ether, trimethylsilyloxybutadiene, or cyclopentadiene with 5-nitro-7,8-furoxanoquinolines was studied in details. Considering that both in solutions and crystals nitrofuroxanoquinoline exists as an inseparable mixture of two N-oxide tautomers, all cycloaddition processes were studied for both of them. The studied mechanisms practically do not depend on the location of the exocyclic oxygen atom in nitrofuroxanoquinoline molecule. At the first step of all reactions the conjugated nitroarene fragments C=C–N=O react with nucleophilic reagents following the mechanism of endo-[4+2] cycloaddition with inverse electronic demand. Further (in the cases of trimethylsilyloxybutadiene and cyclopentadiene) endo-[4+2] cycloadducts recyclize spontaneously according to the mechanism of [3,3] sigmatropic rearrangement into more thermodynamically stable, experimentally detected endo-[2+4] cycloadducts. Both endo-[4+2] and endo-[2+4] cycloadducts obtained from cyclopentadiene and nitrofuroxanoquinoline have been experimentally isolated and characterized. For this case, the kinetic and activation parameters of [4+2] → [2+4] transformation have been studied by 1H NMR method, which have shown an excellent agreement with quantum-chemical results. In all cases the exo processes are one-step reactions, less favorable kinetically than their endo competitors.

Synthesis, spectral analysis and study of antimicrobial activity of 2,5-diformyl-1H-pyrrole bis(methan-1-yl-1-ylidene)dimalonohydrazone

We have synthesized 2,5-diformyl-1H-pyrrole bis(methan-1-yl-1-ylidene)dimalonohydrazone (DPBMD) and characterized by elemental analysis, FT-IR, UV–Vis, Mass, 1H and 13C NMR spectroscopy. Theoretical calculations were performed by ab initio RHF and density functional theory (DFT)/B3LYP method, 6-31G(d,p) and 6-311++G(d,p) basis sets. The calculated scaled vibrational frequency values have been compared with experimental FT-IR spectrum. The calculated result shows excellent agreement between experimental and calculated frequencies at B3LYP method and 6-311++G(d,p) basis set. The thermodynamics properties, NBO, nonlinear optical properties and mulliken charges of DPBMD have also been analyzed. Involvement of nitrogen [N8/N18] and [N14/N24] lone pairs of electron with [π∗(C9–O10), π∗(C6–N7)/π∗(C16–N17), π∗(C19–O20)] and [(π∗(C12–O13)/π∗(C22–O23)] leads to an enormous stabilization of 84.6/84.6 and 64.1/64.1kcal/mol of the molecule. A combined experimental and theoretical stretching wavenumber symmetric (3003, 3332cm−1) and asymmetric (3276, 3398cm−1) analysis confirms free NH2 groups in DPBMD. The calculated first hyperpolarizability (β0=5.80×10−30esu) at B3LYP method and 6-311++G(d,p) basis sets indicates that DPBMD can be used as an attractive material for non-linear optical. The electronic descriptor analysis indicates that DPBMD is a good precursor for heterocyclic synthesis and as ligand for metal complex formation. The preliminary bioassay suggested that the DPBMD compound exhibits relatively good antibacterial and fungicidal activity against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pyogenes, Candida albicans, and Aspergillus niger.

Vibrational spectra, electronic absorption, nonlinear optical properties, evaluation of bonding, chemical reactivity and thermodynamic properties of ethyl 4-(1-(2-(hydrazinecarbonothioyl)hydrazono)ethyl)-3,5-dimethyl-1H-pyrrole-2-carboxylate molecule by ab initio HF and density functional methods

In this work, detailed vibrational spectral analysis of ethyl 4-(1-(2-(hydrazinecarbonothioyl)hydrazono)ethyl)-3,5-dimethyl-1H-pyrrole-2-carboxylate (EHCHEDPC) molecule has been carried out using FT-IR spectroscopy and potential energy distribution (PED). Theoretical calculations were performed by ab initio RHF and density functional theory (DFT) method, using 6-31G(d,p) and 6-311+G(d,p) basis sets. The other carried outwork cover: structural, thermodynamic properties, electronic transitions, bonding, multiple interaction, chemical reactivity and hyperpolarizability analysis. The results of the calculation were applied to the simulated spectra of (EHCHEDPC), which show excellent agreement with observed spectra. The vibrational analysis shows red shift in both group, the proton donor (pyrrole NH) and proton acceptor (CO of ester) indicating the presence of intermolecular hydrogen bonding. Time dependent density functional theory (TD-DFT) has been used to find electronic excitations and their nature. The results of natural bond orbital (NBOs) analysis show the charges transfer and delocalization in various intra- and intermolecular interactions. The binding energy of intermolecular multiple interactions is calculated to be 12.54kcalmol−1 using QTAIM calculation. The electronic descriptors analyses reveal the investigated molecule used as precursor for heterocyclic derivatives synthesis. First hyperpolarizability (β0) has been computed to evaluate non-linear optical (NLO) response.

Experimental and DFT studies on the vibrational and electronic spectra of 9-p-tolyl-9H-carbazole-3-carbaldehyde

The compound 9-p-tolyl-9H-carbazole-3-carbaldehyde (HCCD) was synthesized and characterized by X-ray diffraction, FT-IR, FT-Raman and UV–Vis spectra. The X-ray diffraction study showed that HCCD has a Z-configuration. The benzene ring including methyl is twisted from the mean plane of the carbazole group by 59.7(3)°, which is comparable with the calculated result 65° for B3LYP/6-311++G(d, p) method. Vibrational spectra and electronic spectra measurements were made for the compound. Optimized geometrical structure and harmonic vibrational frequencies were computed with B-based DFT (BLYP, B3LYP and cam-B3LYP) methods, and WB-based DFT (WB97, WB97X and WB97XD) methods and ab initio RHF method using 6-311++G(d, p) basis set. Assignments of the observed spectra were proposed. The equilibrium geometries computed by all of the methods were compared with X-ray diffraction results. The absorption spectra of the title compound were computed both in gas phase and in DMF solution using TD-(cam)B3LYP/6-311++G(d, p) and PCM-(cam)B3LYP/6-311++G(d, p) approaches, respectively. The calculated results provide good descriptions of the bands maxima in the observed electronic spectrum. Temperature dependence of thermodynamic parameters in the range of 100–1000K was determined. The natural atomic hybrids were calculated and discussed.

Experimental and DFT studies on the vibrational and electronic spectra and NBO analysis of 2-amino-3-((E)-(9-p-tolyl-9H-carbazol-3-yl) methyleneamino) maleonitrile

2-Amino-3-((E)-(9-p-tolyl-9H-carbazol-3-yl) methyleneamino) maleonitrile (ACMM) was synthesized and characterized by X-ray diffraction, FT-IR, FT-Raman and UV–Vis spectra. The X-ray diffraction study showed that ACMM has a Z-configuration, due to the intramolecular C18H18A⋯N2, N3H3A⋯N2 and C20H20A⋯N4 hydrogen bonds and intermolecular C10H10A⋯N4, N3H3B⋯N9 (2−x, 2−y, 2−z) and N3H8C⋯N4 (2−x, 1−y, 2−z) hydrogen bonds. The benzene ring including methyl is twisted from the mean plane of the carbazole group by 59.7(3)°. Vibrational spectra and electronic spectra measurements were made for the compound. Optimized geometrical structure and harmonic vibrational frequencies were computed with DFT (B3-based B3P86, B3LYP, B3PW91 and B-based BP86, BLYP, BPW91) methods and ab initio RHF method using 6-311++G(d, p) basis set. Assignments of the observed spectra were proposed. The equilibrium geometries computed by all of the methods were compared with X-ray diffraction results. The absorption spectra of the title compound were computed both in gas phase and in DMF solution using TD-B3LYP/6-311++G(d, p) and PCM-B3LYP/6-311++G(d, p) approaches, respectively. The calculated results provide a good description of positions of the bands maxima in the observed electronic spectrum. Temperature dependence of thermodynamic parameters in the range of 100–1000K were determined. The bond orbital occupancies, contribution from parent natural bond orbital (NBO), the natural atomic hybrids was calculated and discussed.

Experimental and DFT studies on the vibrational, electronic spectra and NBO analysis of thiamethoxam

Vibrational and electronic spectral measurements were performed for 3-(2-chloro-1,3-thiazol-5-ylmethyl)-5-methyl-1,3,5-oxadiazinan-4-ylidene(nitro) amine (thiamethoxam). Optimized geometrical structure and harmonic vibrational frequencies were calculated with ab initio RHF and DFT (B3LYP, CAMB3LYP, M06 and PBE1PBE) methods with 6-311++G (d, p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed in gas-phase using TD-B3LYP/6-311++G (d, p) approach and H2O solution using PCM-TD-B3LYP/6-311++G (d, p) approach. The calculated results matched well with the experimental values. Temperature dependence of thermodynamic parameters in the range of 100–1000K were determined. The bond orbital occupancies, contribution from parent natural bond orbital (NBO), the natural atomic hybrids was discussed.

Electronic absorption, vibrational spectra, nonlinear optical properties, NBO analysis and thermodynamic properties of N-(4-nitro-2-phenoxyphenyl) methanesulfonamide molecule by ab initio HF and density functional methods

In this work, the vibrational spectral analysis was carried out by using FT-Raman and FT-IR spectroscopy in the range 4000–100cm−1 and 4000–400cm−1, respectively, for N-(4-nitro-2-phenoxyphenyl) methanesulfonamide molecule. Theoretical calculations were performed by ab initio RHF and density functional theory (DFT) method using 6-31G(d,p) and 6-311G(d,p) basis sets. The complete vibrational assignments of wavenumbers were made on the basis of potential energy distribution (PED). The results of the calculations were applied to simulated spectra of the title compound, which show excellent agreement with observed spectra. The frontier orbital energy gap and dipole moment illustrates the high reactivity of the title molecule. The first order hyperpolarizability (β0) and related properties (μ, α and Δα) of the molecule were also calculated. Stability of the molecule arising from hyperconjugative interactions and charge delocalization were analyzed using natural bond orbital (NBO) analysis. The results show that electron density (ED) in the σ* and π* anti-bonding orbitals and second order delocalization energies (E2) confirm the occurrence of intramolecular charge transfer (ICT) within the molecule. UV–vis spectrum of the compound was recorded in the region 200–500nm in ethanol and electronic properties such as excitation energies, oscillator strength and wavelength were calculated by TD-DFT/B3LYP, CIS and TD-HF methods using 6-31G(d,p) basis set. Molecular electrostatic potential (MEP) and HOMO–LUMO energy levels are also constructed. The thermodynamic properties of the title compound were calculated at different temperatures and the results reveals the heat capacity (C), and entropy (S) increases with rise in temperature.

Natural Bond Orbital (NBO) Population Study of Some Para-Substituted N-Methyl-N-nitrosobenzenesulfonamide Biological Molecules in MeCN Solution

A theoretical study of several para-substituted N-methyl-N-nitrosobenzenesulfonamide biological molecules in MeCN solution has been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with the 6-311++G(d,p) basis set. Geometries obtained from DFT calculations were used to perform natural bond orbital analysis. The results show that an intramolecular hydrogen bond exists in the selected molecules, which is confirmed by the NBO analysis. The p characters of the two nitrogen natural hybrid orbitals \( \sigma_{{{\text{N}}3 - {\text{N}}2}} \) increase with increasing \( \sigma_{p} \) values of the para-substituent group on the benzene ring, which results in a lengthening of the N3–N2 bond. It is noted that the weakness of the N–N bond is due to \( n_{{{\text{O}}1}} \to \sigma_{{{\text{N}}3 - {\text{N}}2}}^{*} \) delocalization and is responsible for the longer N3–N2 bond. In addition, there is a direct correlation between hyperconjugation \( n_{{{\text{O}}1}} \to \sigma_{{{\text{N}}3 - {\text{N}}2}}^{*} \) and the bond dissociation energy in the system, which is confirmed by comparison with isoelectronic isomers.

Ab initio study of the structure and stability of AcF n (3 − n)+ of complexes (n = 1−7)

The structural and energetic characteristics of AcF n (3 − n)+ complexes (n = 1−7) have been calculated by the ab initio RHF and MP2 methods.

Theoretical investigation of some N-nitrosodiphenylamine biological molecules — A natural bond orbital (NBO) study

Theoretical study of several N-nitrosodiphenylamine biological molecules has been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6–311G++(d,p) basis set. Geometries obtained from density functional theory (DFT) calculations were used to perform Natural bond orbital (NBO) analysis. The p characters of two nitrogen natural hybrid orbitals (NHOs) σN3−N2 increase with increasing σp values of the substituents on the benzene, which results in a lengthening of the N3–N2 bond. The p characters of oxygen NHO σO1−N2 and nitrogen NHO σO1−N2 bond orbitals decrease with increasing σp values of the substituents on the benzene, which results in a shortening of the N2=O1 bond. It is also noted that decreased occupancy of the localized σN3−N2 orbital in the idealized Lewis structure, or increased occupancy of [Formula: see text]of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are also related to the resulting p character of the corresponding nitrogen NHO of σN3−N2 bond orbital.

Experimental and DFT studies on the vibrational and electronic spectra of 4,5-dihydro-6-methyl-4-[(E)-(3-pyridinylmethylene)amino]-1,2,4-triazin-3(2H)-one

Vibrational and electronic spectral measurements were made for 4,5-dihydro-6-methyl-4-[(E)-(3-pyridinylmethylene)amino]-1,2,4-triazin-3(2H)-one (pymetrozine). Optimized geometrical structure and harmonic vibrational frequencies were computed by ab initio RHF, B-based DFT methods (BLYP, BP86 and BPW91) and B3-based DFT methods (B3LYP, B3P86 and B3PW91) using 6-311++G(d,p) basis set. Complete assignments of the observed spectra were proposed. The absorption spectra of the compound were computed both in gas-phase and in C 2H 5OH solution using TD-B3LYP/6-311++G(d,p) and PCM-B3LYP/6-311++G(d,p) approaches, respectively, the calculated results provide a good description of positions of the bands maxima in the observed electronic spectrum. The MEP calculation indicates that the most possible site for electrophilic attack is H23 and the most possible sites for nucleophilic attack are N5 and O19.

Theoretical investigation of some O-nitrosyl carboxylate biologic molecules — A natural bond orbital study

Theoretical study of several O-nitrosyl carboxylate compounds have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G** basis set. Geometries obtained from DFT calculations were used to perform the natural bond orbital (NBO) analysis. It is noted that weakness in the O3-N2 bond is due to $$ n_{O_1 } \to \sigma _{O_3 - N_2 }^* $$ delocalization and is responsible for the longer O3-N2 bond lengths in O-nitrosyl carboxylate compounds. It is also noted that decreased occupancy of the localized $$ \sigma _{O_3 - N_2 } $$ orbital in the idealized Lewis structure, or increased occupancy of $$ \sigma _{O_3 - N_2 }^* $$ of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital (NHO) of $$ \sigma _{O_3 - N_2 } $$ bond orbital. In addition, the charge transfer energy decreases with the increase of the Hammett constants of subsitutent groups.

Experimental and DFT studies on the vibrational and electronic spectra of 1,5-dimethyl-2-phenyl-4-[(pyridin-4-ylmethylene)-amino]-1,2-dihydro-pyrazol-3-one

Vibrational spectral measurements were made for 1,5-dimethyl-2-phenyl-4-[(pyridin-4-ylmethylene)-amino]-1,2-dihydro-pyrazol-3-one (DPPDP). Optimized geometrical structure and harmonic vibrational frequencies were computed by ab initio RHF and DFT (B-based BP86, BLYP, BPW91, B3-based B3P86, B3LYP, B3PW91 and O3-based O3LYP) methods using 6-311++G(d,p) basis set. Complete assignments of the observed spectra were proposed. The equilibrium geometries computed by all of the methods, were compared with X-ray diffraction results. The absorption spectra of the title compound were computed both in gas phase and in CH 3CN solution using TD-B3LYP/6-311++G(d,p) and PCM-B3LYP/6-311++G(d,p) approaches and the calculated results provide a good description of positions of the two band maxima in the observed electronic spectrum.

Natural bond orbital (NBO) population analysis of some benzyl nitrites

Theoretical study of several benzyl nitrites have been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G∗∗ basis set. Geometries obtained from DFT calculations were used to perform NBO analysis. It is noted that weakness in the O 3–N 2 sigma bond is due to n O 1 → σ O 3 – N 2 ∗ delocalisation and is responsible for the longer O 3–N 2 bond lengths in the selected benzyl nitrites. It is also noted that decreased occupancy of the localized σ O 3 – N 2 orbital in the idealized Lewis structure, or increased occupancy of σ O 3 – N 2 ∗ of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital (NHO) of σ O 3 – N 2 bond orbital. In addition, the charge transfer energy decreases with the increasing of the Hammett constants of substituent groups.

Conformational analysis of cis- and trans-isomers of 2,5-dimethyl-1,3-dioxane

The conformational isomerization of cis- and trans-isomers of 2,5-dimethyl-1,3-dioxane was investigated by means of ab initio RHF//6-31G(d) and PBE//ccpVDZ quantum-chemical methods. It has been shown that in comparison with cis-form the potential energy surface of trans-isomer has a less number of stationary points and includes the main minimum belonging to the diequatorial chair form. In the case of cisisomer the main minimum corresponds to the C 2e5a chair form. The values of potentional barriers of conformational isomerization were also determined. On the basis of experimental (NMR 1H) and theoretical vicinal coupling constants we determine the value ΔG 0 of chair-chair inversion for the trans-isomer molecule.

Natural bond orbital analysis of some S-nitrosothiols biological molecules

Theoretical study of several S-nitrosothiols biological molecules has been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6-31G(d,p) basis set. Geometries obtained from DFT calculations were used to perform natural bond orbital (NBO) analysis. It is noted that the weakness in the SN sigma bond is due to nO1σ delocalization and is responsible for the longer SN bond length in S-nitrosothiols. It is also noted that decreased occupancy of the localized σSN orbital in the idealized Lewis structure or increased occupancy of σ of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital of σSN bond orbital. In addition, the charge transfer energy decreases with the increasing of the Hammett constants of substituent groups, and the partial charge distribution on the skeletal atoms shows that the electrostatic repulsion or attraction between atoms can give a significant contribution to the intramolecular and intermolecular interaction. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010