Elizete Ventura

• Federal University of Paraíba

Normally, carbocations and carbanions of hydrocarbons react to form a CC σ bond. However, if the ions are very stable with a large steric repulsion between them, one can also have the formation of an ion pair, generally much less stable than the covalent form. For an extremely large steric repulsion in the covalent form, the ion pair can become th...

The infrared (IR) spectrum of meta ‐fluorothiophenol (mFTP) isolated in a low‐temperature N 2 matrix was recorded and interpreted with the aid of B3LYP vibrational frequency calculations for both cis and trans conformers. Then, photochemical transformations in the matrix‐isolated compound were triggered through UV–Vis laser irradiations and their o...

For many years researchers believed that hydrocarbons only contain covalent bonds. However, since 1985 Okamoto et al. demonstrated the formation of hydrocarbon salts in several systems, demolishing the structural principle that hydrocarbons only contain covalent bonds. Despite the great importance of this outcome to the study of chemical bonds, qua...

A semi-analytical solution for the time dependence of the concentration of the intermediate is derived, in the case of two parallel mixed second order reactions followed by a first order reaction. The solution is restricted to equal initial concentrations for the reactants, and it is connected to the exponential integral. From the solution and thro...

Although CH 2 FCl (HCFC‐31) recently became of great atmospheric importance, studies concerning its excited states are almost nonexistent. Several excited singlet states were studied (valence nσ* and Rydberg n3s, n3p, σ3s, and σ3p) through highly correlated multireference configuration interaction with singles and doubles, including extensivity cor...

An active environment is any atomic or molecular system changing a chromophore's nonadiabatic dynamics compared to the isolated molecule. The action of the environment on the chromophore occurs by changing the potential energy landscape and triggering new energy and charge flows unavailable in the vacuum. Surface hopping is a mixed quantum-classica...

A complex environment is any atomic or molecular system changing a chromophore's nonadiabatic dynamics compared to the isolated molecule. The action of the environment on the chromophore occurs by changing the potential energy landscape and triggering new energy and charge flows unavailable in the vacuum. Surface hopping is a mixed quantum-classica...

Organic molecules are a potential source of prebiotic chemistry in the interstellar medium (ISM). Methanol (MetOH) is a very important source of more complex molecules. H3O⁺(aq) and Cl⁻(aq) are fundamental to living organisms and can be generated in the ISM from the dissociation of HCl with just four water molecules, yielding the (H3O)⁺(H2O)3Cl⁻ io...

Pyrene fluorescence after a high-energy electronic excitation exhibits a prominent band shoulder not present after excitation at low energies. The standard assignment of this shoulder as a non-Kasha emission from the second-excited state (S 2 ) has been recently questioned. To elucidate this issue, we simulated the fluorescence of pyrene using two...

Pyrene fluorescence after a high-energy electronic excitation exhibits a prominent band shoulder not present after excitation at low energies. The standard assignment of this shoulder as a non-Kasha emission from the second-excited state (S2) has been recently questioned. To elucidate this issue, we simulated the fluorescence of pyrene using two di...

Correction for ‘Modeling the heating and cooling of a chromophore after photoexcitation’ by Elizete Ventura et al. , Phys. Chem. Chem. Phys. , 2022, 24 , 9403–9410, https://doi.org/10.1039/D2CP00686C.

The heating of a chromophore due to internal conversion and its cooling down due to energy dissipation to the solvent are crucial phenomena to characterize molecular photoprocesses. In this work, we simulated the ab initio nonadiabatic dynamics of cytosine, a prototypical chromophore undergoing ultrafast internal conversion, in three solvents-argon...

The occurrence of a hydrogen‐bonded contact ion pair (HBCIP, in the gas phase) between the dibenzotropylium cation and chloride has been suggested previously. However, the low barrier (ΔE‡, of ~1 kcal/mol) to its covalent counterpart can preclude its detection. In this work it is shown (through density functional theory calculations) that ΔE‡ can b...

Understanding the mechanism responsible for peroxides decomposition is essential to explain several biochemical processes. The mechanisms of the intrinsic reactions between the superoxide radical anion (O2•‒) and methyl, ethyl, and tert-butyl hydroperoxides (ROOH, with R = Me, Et, and t-Bu) have been characterized to understand the mechanism respon...

So far, no conclusive evidence of a ground-state contact ion-pair containing a hydrocarbon carbocation has been given in the gas phase. Due to the very high stability of the 1,2:4,5-dibenzotropylium (or dibenzo[a,d]tropylium) carbocation, we suggest (supported by DFT and MP2 calculations) the formation of a contact ion pair between this carbocation...

For the first time, multireference configuration interaction with singles and doubles (MR‐CISD) calculations (including extensivity corrections, MR‐CISD+Q) have been performed to study the ring‐opening reactions of the following mesoionic rings and their 2, 3, and 4 methyl‐substituted derivatives: (a ) 1,3‐oxazol‐5‐one, (c ) 1,3‐oxazol‐5‐thiolate,...

Multi‐reference configuration interaction, MR‐CI (including extensivity corrections, named +Q), calculations were performed on the S0–S3 states of cyclohexa‐2,4‐diene‐1‐thione (thione 24 ) and cyclohexa‐2,5‐diene‐1‐thione (thione 25 ), which are thione isomers of thiophenol. Several types of uncontracted MR‐CIS and MR‐CISD wavefunctions were employ...

The core part of the program system COLUMBUS allows highly efficient calculations using variational multireference (MR) methods in the framework of configuration interaction with single and double excitations (MR-CISD) and averaged quadratic coupled-cluster calculations (MR-AQCC), based on uncontracted sets of configurations and the graphical unita...

Details concerning the energetics and structure of the ion pair in gaseous chloroethane, obtained at the multi-reference configuration interaction with singles and doubles (MR-CISD) level, are given. It is formed in the third excited state (31A′), and it can be classified as a hydrogen-bonded contact ion pair, although from its total binding energy...

High-level multireference electronic structure calculations have been performed to study the Cl⁻ yield from photoexcited CF3CH2Cl (HCFC-133a). The analysis of this process tells that it relates to an electron transfer from the carbon to the Cl atom, forming a highly polar contact ion-pair complex, CF3HCH⁺∙∙∙Cl⁻, in the excited (S3) state. This comp...

For the first time, high-level multireference electronic structure calculations have been performed to study the photochemistry of CF3Cl, allowing a comprehensive interpretation and assignment of experimental data concerning fluorescence, ion-pair formation, and generation of CF3 fragments in several electronic states. All studied dissociation chan...

Highly correlated calculations at the multi-reference configuration interaction levels including singles and doubles excitations (MR-CISD) and extensivity corrections (MR-CISD + Q) have been performed to study some low-lying valence and Rydberg states of the CF3 radical. Our highest level results (at the MR-CISD + Q level) yield the following energ...

Supplementary

The mechanism of the O2⋅− and H2O2 reaction (Haber–Weiss) under solvent-free conditions has been characterized at the DFT and CCSD(T) level of theory to account for the ease of this reaction in the gas phase and the formation of two different set of products (Blanksby et al., Angew. Chem. Int. Ed. 2007, 46, 4948). The reaction is shown to proceed t...

We disclose here the studies that preceded and guided the preparation of the metal-based, redox-active therapeutic Mn(III) meso-tetrakis(N-n-butoxyethylpyridyl)porphyrin, MnTnBuOE-2-PyP5 + (BMX-001), which is currently in Phase I/II Clinical Trials at Duke University as a radioprotector of normal tissue in cancer patients. N-substituted pyridylporp...

DFT calculations have been applied in order to study the free energies of the structures corresponding to the three different protonation sites of N,N-dimethylnitrosamine (DMNA). The solvent effect has been taken into account through the study of clusters consisting of protonated DMNA and up to four explicit water molecules, either in the absence o...

State-of-the-art electronic structure calculations (MR-CISD) are used to map five different dissociation channels of CH3Cl along the C - Cl coordinate: i) CH3( X(2)A2´´) + Cl((2)P), ii) CH3(3s(2)A1´) + Cl((2)P), iii) CH3(+)((1)A1´) + Cl(-)((1)S), iv) CH3(3p (2)E´) + Cl((2)P), and v) CH3(3p (2)A2´´) + Cl((2)P). By the first time these latter four di...

The UV-induced photochemistry of HCFC-132b (CF2 ClCH2 Cl) was investigated by computing excited-state properties with time-dependent density functional theory (TDDFT), multiconfigurational second-order perturbation theory (CASPT2), and coupled cluster with singles, doubles, and perturbative triples (CCSD(T)). Excited states calculated with TDDFT sh...

A number of model Diels-Alder (D-A) cycloaddition reactions (H2 CCH2 + cyclopentadiene and H2 CCHX + 1,3-butadiene, with X = H, F, CH3 , OH, CN, NH2 , and NO) were studied by static (transition state - TS and IRC) and dynamics (quasiclassical trajectories) approaches to establish the (a)synchronous character of the concerted mechanism. The use of...

MR-CISD, MR-CISD+Q, and MR-AQCC calculations have been performed on the minima and transition states (corresponding to intramolecular proton transfer between the protonation sites) of the ground state of protonated nitrosamine and N,N-dimethylnitrosamine. Our highest level results (MR-AQCC/cc-pVTZ) for the smaller system indicate that protonation o...

In this work ten singlet and nine triplet states are studied through multi-reference configuration interactions with singles and doubles (MR-CISD), including Davidson extensivity correction (MR-CISD+Q). For the first time the excited states whose energies are larger than 9.5 eV have been calculated using highly correlated methods. The energies, spa...

The energetics of the ECO2, SN2@C and SN2@N channels of X− + CH3ONO2 (X = F, OH, CH2CN) gas-phase reactions were computed using the CCSD(T)/CBS method. This benchmark extends a previous study with X = OH [M. A. F. de Souza et al., J. Am. Chem. Soc. 2012, 134, 19004] and was used to ascertain the accuracy and robustness of nineteen density-functiona...

The photochemical deactivation process of HCFC-133a (C2H2F3Cl) was investigated by computing excited-state properties with a number of single-reference methods, including coupled cluster to approximated second order (CC2), algebraic diagrammatic construction to second order (ADC(2)), and time-dependent density functional theory (TDDFT). Excited sta...

The vertical ionization energies of the chlorine lone pairs in HCFC-133a have been calculated at the SCF (via Koopmans' theorem and including orbital relaxation) and correlated (ROMP2, OVGF, and ROCCSD(T)) levels. Dunning aug-cc-pVXZ (X = D, T, and Q) basis sets were employed, and the ROMP2 and ROCCSD(T) results were extrapolated to the complete ba...

The gas-phase dehydration-rearrangement (DR) reactions of protonated alcohols [Me2 (R)CCH(OH2 )Me](+) [R=Me (ME), Et (ET), and iPr (I-PR)] were studied by using static approaches (intrinsic reaction coordinate (IRC), Rice-Ramsperger-Kassel-Marcus theory) and dynamics (quasiclassical trajectory) simulations at the B3LYP/6-31G(d) level of theory. The...

The unusual O-coordination mode of nitrosamines to Fe(III) heme models has been observed in the bis(dimethylnitrosamine)(meso-tetraphenylporphyrinate)iron(III) cation. For the first time, this latter as well as the simpler bis(dimethylnitrosamine)(porphinate)iron(III) heme model cations have been studied through ab initio methods. The sextet, quart...

The molecular structure and infrared spectrum of the atmospheric pollutant 1,1,1-trifluoro-2-chloroethane (HCFC-133a; CF3CH2Cl) in the ground electronic state were characterized experimentally and theoretically. Excited state calculations (at the CASSCF, MR-CISD, and MR-CISD+Q levels) have also been performed in the range up to ∼9.8 eV. The theoret...

The low-lying n−4s (S2 and T2) and n−4pe (S3 and T3) Rydberg states of the CF3Cl have been studied at the CASSCF, MR–CISD, MR–CISD + Q and MR–AQCC levels using the mixed aug–cc–pVDZ/d–aug–cc–pVDZ and aug′–cc–pVTZ/d′–aug′–cc–pVTZ basis sets. Spin–orbit corrections for the singlet energies, vertical excitation energies and oscillator strengths have b...

In this paper the effect of hydrogen substitution by fluorine on the dipole moment and static isotropic polarizabilities of N-nitrosodimethylamine has been studied through ab initio (MP2) and DFT (B3LYP) calculations with the cc-pVTZ basis set. It has been found that most of the 40 different substitution patterns lead to a decrease of dipole moment...

Ab initio and DFT calculations have been performed to characterize some ground state structures of the title molecules. Relative energies, rotational barriers, NBO charges, and dipole moments (µ) have been calculated and analyzed. It has been confirmed that only highly correlated methods (e.g., CCSD) are able to yield the non-planar structure as a...

Ab initio (MP2) and DFT (B3LYP) calculations, using the cc-pVTZ and aug-cc-pVTZ basis sets, have been performed to characterize some stationary points on the ground state potential energy surface of the title molecules. Several properties as, for instance, relative energies, the barriers for NO rotation around the NN bond, NBO charges on O and amin...

Hartree's original ideas are described. Its connection with electrostatics can be explored in order to decrease the gap between teaching of Physics and Chemistry. As a consequence of its simplicity and connection with electrostatics, it is suggested that Hartree's method should be presented before the Hartree-Fock method. Besides, since the fundame...

Complete active space self-consistent field (CASSCF) and multireference CI with singles and doubles (MR-CISD) calculations [including extensivity corrections, at MR-CISD+Q and multireference averaged quadratic coupled cluster (MR-AQCC) levels] have been performed to characterize the low-lying valence and the Rydberg states of 2H-tetrazole. The high...

DFT calculations with B3LYP and PBE1PBE functionals and 6–311++G(d,p) basis set have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the RCN⋯HF H-bonded complexes with R = NH2, CH3O, CH3, OH, SH, H, Cl, F, CF3, CN and NO2. As expected, it has been verified as a red-shift of the HF stretching fr...

The molecular structure and infrared spectrum of the atmospheric pollutant 3,3-dichloro-1,1,1-trifluoropropane (HCFC-243) were characterized experimentally and theoretically. The theoretical calculations show the existence of two conformers, with the gauche (G) and trans (T) orientation around the HCCC dihedral angle. Conformer G was calculated to...

Recebido em 30/10/06; aceito em 26/10/07; publicado na web em 9/4/08 TEACHING ORGANIC REACTIONS USING COMPUTATIONAL CHEMISTRY: I. ELECTROPHILIC ADDITION REACTIONS TO ALKENES. Basic concepts that play an important role in some organic reactions are revisited in this paper, which reports a pedagogical experience involving undergraduate and graduate s...

Several conformers of the bioactive Morita–Baylis–Hillman adducts (MBHA) 1–4 were studied. Relaxed potential energy surfaces scan (RPESS) have been performed. The principal structures obtained from RPESS approach were then fully optimized at B3LYP/6-311++G∗∗ level and with PCM model simulating water media at B3LYP/6-31+G∗ level. The relative stabil...

Basic concepts that play an important role in some organic reactions are revisited in this paper, which reports a pedagogical experience involving undergraduate and graduate students. A systematic procedure has been applied in order to use widespread available computational tools. This paper aims to discuss the use of computers in teaching electrop...

Extended complete active space self-consistent field (CASSCF), multireference configuration interaction with singles and doubles (MR-CISD), and multireference average quadratic coupled cluster (MR-AQCC) calculations have been performed on the ground (S(0)) and first excited (nsigma(*),S(1)) states of the CF(3)Cl molecule. Full geometry optimization...

Theoretical investigations concerning the formation of hydrogen bonds in both homomeric, (HCN)n, and heteromeric clusters of the type (HCN)nHF (n = 1, 2, and 3) have been performed through ab initio molecular orbital calculations at the second-order Møller–Plesset (MP2) and density functional theory (DFT)/B3LYP levels, with the 6-311++G(d,p) basis...

The optimised geometries of heterocyclic hydrogen-bonded complexes, C2H4O...HX and C3H6O...HX, where X=F or Cl, were determined at DFT/B3LYP/6-311++G(d,p) computational level. Structural, electronic and vibrational properties of these complexes are used in order to compare the strained ring, which confer the great reactivity of these heterocyclic r...

The recently defined Sparkle/AM1 model is now extended to Er(III) and Ce(III), using the same parameterization scheme. Thus, a set of fifteen complexes for each lanthanide ion, with various representative ligands of high crystallographic quality (R factor < 0.05 angstrom), and which possess oxygen and/or nitrogen as coordinating atoms, was used as...

The present manuscript reports a systematic investigation of the basis set dependence of some properties of hydrogen-bonded (pi type) complexes formed by propyne and a HX molecule, where X=F, Cl and CN. The calculations have been performed at Hartree-Fock, MP2 and B3LYP levels. Geometries, H-bond energies and vibrational have been considered. The m...

The effects of CC bond type (double or triple), substituent (H or methyl), and halogen (F and Cl) on three properties of hydrogen-bonded complexes formed between unsaturated hydrocarbons and HX (XF, Cl) are studied. The properties comprise hydrogen bond distances (RH), stabilization energies (SE), and frequency shifts (Δν). A 23 factorial design te...

MP2/6-31++G** and B3LYP/6-31++G** ab initio molecular orbital calculations have been performed in order to obtain molecular geometries, binding energies and vibrational properties of the C2H2-HF, C2H(CH3)-HF and C2(CH3)2-HF H-bonded complexes. As expected, the more pronounced effects on the structural properties of the isolated molecules due to com...

The two-level factorial design (FD) and principal component analysis (PCA) chemometric techniques were used to investigate the carbon–hydrogen bond lengths dependence on the basis set size and quantum chemistry method, for H–C≡CH, H–C≡CF, H–C≡CCH3, H–C≡CCN, H–C≡CCl and H–C≡CCCH molecular systems. The calculations were performed by using Hartree-Foc...

Two-level factorial design (FD) and principal component (PC) models are used to determine the effects of wave function modifications on calculated carbon–carbon triple bond lengths for the HCCH, HCCF, HCCCH3, CH3CCCH3 and HCCCCH molecules. Our results have shown that valence, diffuse and polarization main effects are significant at the three levels...

The results of a highly diastereoselective epoxidation of allylic diols derived from Baylis-Hillman adducts are reported. The formation of an intramolecular hydrogen bond seems to be responsible for the high anti diastereoselection obtained in this epoxidation reaction. The results are complementary to those obtained in the direct epoxidation of Ba...

The dependence of Δ and of the decay constant (β) on the methylene-adjacent benzene dihedral angle (θ), for thermal electron transfer in [CH2–(phenylene)n–CH2]− (n=1,2,3) model systems, is studied. Closed-shell Hartree–Fock (RHF) ab initio, through use of Koopmans theorem (KT), open-shell HF (ROHF) and multiconfigurational SCF (MCSCF) level calcula...

The concerted and stepwise mechanisms of the Diels-Alder reaction between 1,3-butadiene and ethene have been investigated using highly correlated multireference methods (MRAQCC) and extended basis sets. Full MRAQCC geometry optimizations have been performed in all cases. The best estimate for the energy barrier of the Diels-Alder reaction is 22 kca...

The stationary points on the potential energy surface (PES) of tetramethylene have been investigated using highly correlated multireference methods and extended basis sets. Full geometry optimization using analytic gradients as well as systematic scans of the PES employing different basis sets show that all minima and most of the saddle points foun...

Full geometry optimizations within given molecular symmetries have been performed on the chair and boat forms involved in the Cope rearrangement of 1,5-hexadiene using highly correlated methods (MR-CISD and MR-AQCC) and extended basis sets. These optimizations are based on analytic gradient procedures developed within the COLUMBUS program system an...

Valence-excited singlet (S1,S2) and triplet (T1–T4) states of acetylene have been studied by means of extended multireference electron correlation techniques (MR-CISD, MR-CISD+Q, and MR-AQCC). Extrapolations to the basis set limit have been performed. Minima and saddle points have been calculated using a recently developed analytic gradient method...

The implementation of the reduced gradient following (RGF) method into the COLUMBUS quantum-chemical program system is reported using the newly developed analytic MR-CISD/AQCC gradient feature. By this combination a very useful tool has been developed for general searches of stationary points on ground- and excited-state energy surfaces. This proce...

Structures of three isomeric 2- and 4- acetyl-5-ethyl-3-tolyl-dihydro-1,2,4-oxadiazoles 1–3 have been determined by X-ray analysis of their single crystals. 2-Acetyl-5-ethyl-3-(p-tolyl)- and 2-acetyl-5-ethyl-3-(m-tolyl)-2,5-dihydro-1,2,4-oxaliazoles 1 and 2 are triclinic whereas 4-acetyl-5-ethyl-3-(p-tolyl)-4,5-dihydro-1,2,4-oxaliazole 3 is monocli...

We investigate the presence of topological twistons in crystalline polyethylene. We describe crystalline polyethylene with a model that couples the torsional and longitudinal degrees of freedom of the polymeric chain by means of a system of two real scalar fields. This model supports topological twistons, which are described by exact and stable top...

We introduce an alternate model to describe twistons in crystalline polyethylene. The model couples torsional and longitudinal degrees of freedom and appears as an extension of a model that describes only the torsional motion. We find exact solutions that describe stable topological twistons, in good agreement with the torsional and longitudinal in...

In this paper we follow the lines of recent works to investigate systems of two coupled real scalar fields defined by potentials that describe periodic interactions between the scalar fields. We work with polymeric chains containing periodic interactions between the coupled fields, and we investigate the topological sectors to obtain explicit solit...