Caio Firme

Caio Firme
Universidade Federal do Rio Grande do Norte | IIP · Departamento de Química

Doctor of Philosophy

About

42
Publications
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306
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Introduction
Caio Firme currently works at the Departamento de Química, Universidade Federal do Rio Grande do Norte. Caio does research in Theoretical Chemistry, Organic Chemistry with main focus in aromaticity, electronic nature of non-trivial systems and mechanisms. He recently published a book entitled: "Introductory Organic Chemistry and Hydrocarbons - A Physical Chemistry Approach" from CRC Press.

Publications

Publications (42)
Article
In our previous work, we developed the local potential energy density model, LPE, based on the electrostatic force and QTAIM topological data with a high linearity with the supramolecular binding energy, SME, for the classical hydrogen bonds. In this work, we extended the investigation to other inter/intramolecular interactions. The LPE presented a...
Article
Alloy clusters of NaxLiy (4 ≤ x + y ≤ 10) are studied by exploring the potential energy surface in the ab initio MP2 level with the support of a quantum genetic algorithm (QGA). In some cases, the structures have been also refined with DFT and coupled-cluster methods. The general trends of sodium-lithium structures are in line with previous studies...
Preprint
p>In previous work, we developed the local potential energy model, LPE, based on the electrostatic force and QTAIM topological data to quantify classical hydrogen bond energies. In this work, we extended the investigation to other inter/intramolecular interactions (non-conventional hydrogen bonds and others). The LPE presented high precision and li...
Article
We developed the local potential energy, LPE, model based on the electrostatic force (the unique fundamental force for chemical bonds) whose equation uses QTAIM topological data. The effectiveness of the LPE was evaluated with other well-known methods (supramolecular binding enthapy, SAPT-DFT, LMOEDA and IQA) by analyzing the hydrogen bond energy f...
Book
Full-text available
A novel proposal for teaching organic chemistry based on a broader and simplified use of quantum chemistry theories and notions of some statistical thermodynamic concepts aiming to enrich the learning process of the organic molecular properties and organic reactions. A detailed physical chemistry approach to teach organic chemistry for undergraduat...
Article
Various kinetic studies of the addition of hydrogen halides to alkenes were carried out in the 1930s, 1940s, and 1970s. Since then, there have been theoretical analyses of several aspects of alkene reactivity and regioselectivity during hydrohalogenation. A few works have studied the influence of the hydrogen halide when it is acting as a catalyst...
Article
Full-text available
A few theoretical and experimental studies have been done so far about the properties and the conformational analysis of alkenes as monomers and dimers. Deeper insights into the conformational analysis of monomers and dimers of alkenes and the relation with boiling point are done in this work. In low-lying cis -butene, there is no repulsive interac...
Article
The aim of this work is to study the La2FeMnO6 double perovskite system from an experimental point of view. The nanoparticles were prepared through the ionic coordination reaction method and have a mean particle size of 36 nm, as determined by MEV analysis. The crystal structure is monoclinic with P21/n space group. The ⁵⁷Fe Mössbauer spectroscopy...
Article
Cyclophanes have several geometric restrictions in their structures due to formation of a closed circuit involving benzenoid rings and aliphatic bridges which cause instability. We have chosen a wider variety of ciclophanes for the ωB97XD analysis of geometry and thermodynamic data. More detailed geometric parameters have been used in this work suc...
Article
The bioactive 19-nor-clerodane trans-dehydrocrotonin (t-DCTN) is herein used as starting material to afford an epimeric derivative mixture so called t-DCTN-α and β-OL, which is a diastereoisomeric pair. The stereoselective reduction of t-DCTN was performed in methanol medium by using NaBH4 and CeCl3·7H2O which react reducing the C2 carbonyl group o...
Article
Although there are a multitude of aromaticity indexes, only a few have a widespread usage. All famous aromaticity indexes are limited: HOMA and FLU are reference-dependent; ELF is π-bond-dependent; PDI is structurally dependent and NICS is ring size dependent. These limitations stimulate the continuous search for better (i.e., having no dependency)...
Article
The 17α-hydroxylase-17,20-lyase (CYP17) is a cytochrome P450 enzyme which participates in steroid hormones metabolism. Pregnenolone (PREG) is its natural steroid substrate and abiraterone (ABE) is a well-known steroid inhibitor. In this paper, QTAIM and NCI analysis indicate many non-familiar intramolecular interactions in CYP17-ABE and CYP17-PREG...
Article
Full-text available
We have applied an undergraduate minicourse of Diels-Alder reaction in Federal University of Rio Grande do Norte. By using computational chemistry tools (Gaussian, Gaussview and Chemcraft) students could build the knowledge by themselves and they could associate important aspects of physical-chemistry with Organic Chemistry. They have performed a v...
Article
Full-text available
There are four types of aromaticity criteria: energetic, electronic, magnetic and geometric. The delocalization, density and degeneracy-based index of aromaticity, D3BIA, is an electronic aromaticity index from QTAIM that is not reference dependent and can be used for aromatic, homoaromatic, sigma aromatic and other aromatic systems with varying ri...
Article
The electronic structure and the stability of tetrahedrane, substituted tetrahedranes and silicon and germanium parents have been studied at ωB97XD/6-311++G(d,p) level of theory. The quantum theory of atoms in molecules (QTAIM) was used to evaluate the substituent effect on the carbon cage in the tetrahedrane derivatives. The results indicate that...
Article
Full-text available
trans-Dehydrocrotonin (t-DCTN) a bioactive 19-nor-diterpenoid clerodane type isolated from Croton cajucara Benth, is one of the most investigated clerodane in the current literature. In this work, a new approach joining X-ray diffraction data, nuclear magnetic resonance (NMR) data and theoretical calculations was applied to the thorough characteriz...
Article
Full-text available
Analytical Chemistry books lack a clear link between thermodynamic and equilibrium approaches involving acids and bases. In this work, theoretical calculations were performed to search for these relations. An excellent relationship was found between difference in Gibbs free energy, ΔG of acid dissociation reaction and ΔG of hydrolysis reaction of t...
Article
The hydrogen-hydrogen (H-H) bond or hydrogen-hydrogen bonding is formed by the interaction between a pair of identical or similar hydrogen atoms that are close to electrical neutrality and it yields a stabilizing contribution to the overall molecular energy. This work provides new, important information regarding hydrogen-hydrogen bonds. We report...
Article
Many undergraduate organic chemistry books do not agree with the order of relative stability of alkenes towards hydrogenation reactions. Although they ascribe the stability of alkenes to the number and spatial position of the alkyl groups attached to the vinyl carbon atoms, results from the quantum theory of atoms in molecules indicate that the inf...
Article
Bent metallocenes are a class of organometallic compounds that are widely used as catalysts in olefin polymerization procedures. We found a linear relation between the relative stability of bent titanocenes and the average delocalization index (DI) for Ti–C (from the cyclopentadienyl ring) atomic pairs within the evaluated compounds. As a consequen...
Article
The highly pyramidalized molecule bisnoradamantene is extremely reactive toward nucleophiles and dienes. In this work, we studied the electronic structure of bisnoaradamantene, as well as those of its cation and dication, which are previously unreported carbonium ions. According to QTAIM and MO analysis, there is a 3c-2e bonding system in the bisno...
Article
The density functional theory (DFT) and quantum theory of atoms in molecules (QTAIM) have been used to study the lowest lying spin states of the photochemical hydrogen abstraction reaction by formaldehyde, acetaldehyde and acetone in the presence of different hydrogen donors: propane, 2-propanol and methylamine. Calculations of all the critical poi...
Article
Full-text available
The assistance of s electron delocalization or anchimeric assistance of s electrons accounts for the large rate differences in the solvolysis of 2-exo- and 2-endo-norbornyl-p-bromobenzenesulfonates. This study was formerly analyzed by molecular orbital theory in gas phase. By revisiting this old problem from the quantum theory of atoms in molecules...
Book
Full-text available
Article
The electronic nature of ferrocene, titanocene and some bent titanocenes was analyzed by QTAIM. PBE1PBE-optimised geometrical data agreed well with X-ray diffraction data, this method being chosen to extract and analyze the wave functions of all studied metallocenes within the QTAIM framework. Within the studied metallocenes, the number of bond pat...
Article
In this work, nine tetrasubstituted derivatives [NH(2), OCH(3), Li, Na, Si(CH(3))(3)/SiH(2)CH(3,) P(CH(3))(2), Cl, F, and CN] of the spiropentadiene dication were analyzed within the framework of QTAIM. In the studied series, the electron-withdrawing substituents destabilize the ptC-containing spiropentadiene dication. On the other hand, stabilizat...
Article
Full-text available
The Gassman-Fentiman tool of increasing electron demand was used to identify carbonium and carbenium ions. Nonetheless, due to its ambiguous understanding, it was pivot of a historical dispute. We applied the Quantum Theory of Atoms in Molecules (QTAIM) metodology to characterize the carbonium and carbenium ions on an easier and more effective way....
Article
The photochemical hydrogen abstraction reaction of pyrene-4,5-dione (3) has been investigated by laser flash photolysis. Excitation (λ = 355 nm) of a degassed solution of 3 in acetonitrile resulted in the formation of a detectable transient with absorption maxima at 380 and 470 nm. This transient decays with a lifetime of around 4.8 μs and is quenc...
Article
Nonclassical ions or carbonium ions have multi-center bonding from delocalized sigma or pi electrons. The 2-norbornyl cation, its derivative 6,6-difluoro-2-norbornyl cation, tris-homocyclopropenyl cation, 7-norbornenyl cation, and 4-cyclopentenyl cation and their corresponding silicon analogues were studied in this work. All carbocations have topol...
Article
The atoms in molecule theory shows that the spiropentadiene dication has a planar tetracoordinate carbon (ptC) atom stabilized mainly through the sigma bonds and this atom has a negative charge. The bonds to the ptC atom have less covalent character than the central carbon from neutral spiropentadiene. The total positive charge is spread along the...
Article
Full-text available
The internet is an important tool for obtaining information. It offers vast amounts of information ranging from basic to advanced, from general to specific. Nevertheless, its quality cannot be classified or graded. Furthermore, some technical and/or specific information may not be available for free. This work primarily shows the great utility of t...
Article
Full-text available
The relative stability of the 1,3-dehydro-5,7-adamantanediyl dication is ascribed to its tridimensional aromaticity. However, its electronic nature is not well known. In order to improve its understanding, dicationic and monocationic adamantanedyil species and some key analogues were studied by atoms in molecules (AIM) theory. They were compared to...
Article
Full-text available
The internet is an important tool for obtaining information. It offers vast amounts of information ranging from basic to advanced, from general to specific. Nevertheless, its quality cannot be classified or graded. Furthermore, some technical and/or specific information may not be available for free. This work primarily shows the great utility of t...
Article
The cyclobutadiene dication was not experimentally characterized to the date. However, some of its derivatives were. Most of them have planar geometry, but tetramethylcyclobutadiene dication has a nonplanar geometry according to ab initio calculations. From the atoms in molecules (AIM) theoretical analysis, common electronic features for the planar...
Article
Laser flash photolysis (LFP) studies, atoms in molecules (AIM) studies, and density functional theory (DFT) calculations have been performed in order to study the mechanism of the hydrogen abstraction by alpha-diketones in the presence of phenols. Laser irradiation of a degassed solution of 1,2-diketopyracene in acetonitrile resulted in the formati...
Article
Full-text available
Aromaticity has been exhaustedly discussed for several years and it remains as a misterious issue. In this work it is proposed a new index of aromaticity named density, degeneracy and delocalization-based index of aromaticity or simply D3BIA in an attempt to cast new insight and perspective over this theme. This index is based on AIM (atoms in mole...
Article
Homogeneous ethylene and propylene polymerisation with new mixed-ligand chloroalcoholate of hafnocene was investigated. The catalytic activity of the complex was studied in comparison with Cp2HfCl2 pre-treated with 2-methyladamantan-2-ol in different molar ratios. The addition of the bridged alicyclic alcohol to the metallocene does not deactivate...
Article
Ethylene and propylene polymerization using Ind(2)ZrCl(2) and Ind(2)Zr(CH3)(2)/ NIAO catalytic systems modified by the sterically demanding bridged alicyclic alcohols, adamantan-1-ol, adamantan-2-ol, 2-methyladamantan-2-ol, and fenchyl alcohol, was investigated. Lower alcohols like isopropanol completely deactivate the system, whereas in the case o...

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