[Show abstract][Hide abstract] ABSTRACT: A coupled-cluster study is carried out to investigate the efficacy of metal(I) cyanide (MCN; M 5 Cu, Ag, Au) compounds to bind with noble gas (Ng) atoms. The MANg bond dissociation energy, enthalpy change, and Gibbs free energy change for the dissociation processes producing Ng and MCN are computed to assess the stability of NgMCN compounds. The Ng binding ability of MCN is then compared with the experimentally detected NgMX (X 5 F, Cl, Br) compounds. While CuCN and AgCN have larger Ng binding ability than those of MCl and MBr (M 5 Cu, Ag), AuCN shows larger efficacy toward bond formation with Ng than that of AuBr. Natural bond orbital analysis, energy decomposition analysis in conjunction with the natural orbital for chemical valence theory, and the topological analysis of the electron density are performed to understand the nature of interaction occurring in between Ng and MCN. The NgAM bonds in NgMCN are found comprise an almost equal contribution from covalent and electrostatic types of interactions. The different electron density descriptors also reveal the partial covalent character in the concerned bonds. V
Journal of Computational Chemistry 09/2015; DOI:10.1002/jcc.24190 · 3.59 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The molecular structures of guaiacol (2-methoxyphenol) and mequinol (4-methoxyphenol) have been studied using high resolution electronic spectroscopy in a molecular beam and contrasted with ab initio computations. Mequinol exhibits two low frequency bands that have been assigned to electronic origins of two possible conformers of the molecule, trans and cis. Guaiacol also shows low frequency bands, but in this case, the bands have been assigned to the electronic origin and vibrational modes of a single conformer of the isolated molecule. A detailed study of these bands indicates that guaiacol has a vibrationally averaged planar structure in the ground state, but it is distorted along both in-plane and out-of-plane coordinates in the first electronically excited state. An intramolecular hydrogen bond involving the adjacent -OH and -OCH3 groups plays a major role in these dynamics.
The Journal of Chemical Physics 09/2015; 143(9):094301. DOI:10.1063/1.4928696 · 2.95 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The usefulness of aromaticity/antiaromaticity concepts to foresee structural stability patterns and salient features of the electronic structure of small inorganic and all-metal rings has been put forward. A critical revision of the advances made in the theoretical methods to assess the aromaticity/antiaromaticity of these compounds has also been made. In particular, the performance of local versus non-local indices has been reviewed. Finally, the passivation of these rings has been put forward as a key issue in order to prevent them from collapsing into larger aggregates and to provide them protection against the environment.
Chemical Society Reviews 06/2015; 44(18). DOI:10.1039/c5cs00341e · 33.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ab initio computations are carried out to assess the noble gas (Ng) binding capability of
BeSO4 cluster. We have further compared the stability of NgBeSO4 with that of the recently
detected NgBeCO3 cluster. The Ng-Be bond in NgBeCO3 is somewhat weaker than that in
NgBeO cluster. In NgBeSO4, the Ng-Be bond is found to be stronger compared to not only the
Ng-Be bond in NgBeCO3 but also that in NgBeO, except the He case. The Ar-Rn bound BeSO4
analogues are viable even at room temperature. The Wiberg bond indices of Be-Ng bonds and
the degree of electron transfer from Ng to Be are somewhat larger in NgBeSO4 than those in
NgBeCO3 and NgBeO. Electron density and energy decomposition analyses are performed in
search of the nature of interaction in Be-Ng bond in NgBeSO4. The orbital energy term (∆Eorb)
contributes the maximum (ca. 80-90%) to the total attraction energy. The Ar/Kr/Xe/Rn-Be bonds
in NgBeSO4 could be called as of partial covalent type with a gradual increase in covalency
along Ar to Rn.
The Journal of Physical Chemistry A 05/2015; DOI:10.1021/acs.jpca.5b03888 · 2.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The global minimum structure of borospherene (B 40) is a cage, comprising two hexagonal and four heptagonal rings. Born-Oppenheimer Molecular Dynamics simulations show that continuous conversions in between six and seven membered rings take place. The activation energy barrier for such a transformation is found to be 14.3 kcal·mol −1. The completely delocalized σ-and π-frameworks, as well as the conservation of the bonding pattern during rearrangement, facilitate the dynamical behavior of B 40. B 40 is predicted to act as a support-free spherical two-dimensional liquid at moderate temperature. In other words, B 40 could be called as a nanobubble. Is it possible to build a buckyball comprising only boron atoms? Boron is an electron deficient atom with only three valence electrons. So, a perfect boron buckminsterfullerene (B 60) is not expected to be stable owing to the absence of the fourth electron, which is essential for the π-stabilization of a spherical shell. A fullerene-like boron cluster, B 80 , was predicted in silico, which has structural similarity with C 60 but with an additional boron atom at the center of each hexagon
[Show abstract][Hide abstract] ABSTRACT: The potential energy surfaces of a series of clusters with the formula CAl3E (E = P, As, Sb, Bi) are systematically explored using density functional theory and high level ab initio calculations. The global minimum structure of these clusters contains a planar tetracoordinate carbon atom. The presence of a C[double bond, length as m-dash]E double bond is supported by the Wiberg bond indices, the adaptive natural density partitioning analysis, and the magnetic response. Our results show that these planar tetracoordinate carbon clusters are both thermodynamically and kinetically viable species in the gas phase.
[Show abstract][Hide abstract] ABSTRACT: The concept of aromaticity was initially introduced in chemistry to account for the stability, reactivity, molecular structures, and other properties of many unsaturated organic compounds. Despite that, it has been extended to other species with mobile electrons including saturated systems, transition structures, and even inorganic molecules. In this review, we focus on the aromaticity of a particular family of organometallic compounds known as metallabenzenes, which are characterized by the formal replacement of a CH group in benzene by an isolobal transition metal fragment. In addition, aromaticity of related compounds such as heterometallabenzenes is considered as well. To this end, we shall describe herein the insight gained by the available experimental data as well as by the application of the state-of-the-art computational methods developed as descriptors for aromaticity together with a critical evaluation of their performance to quantitatively estimate the strength of aromaticity of these systems.
Chemical Society Reviews 02/2015; 44(18). DOI:10.1039/c5cs00004a · 33.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The potential energy surface of the ethanol dimer is systematically explored via density functional theory and high level ab initio computations. A picture with a multitude of local minima very close in energy emerges. Three groups of interactions are at play stabilizing the dimers. On one hand, electrostatic attraction leads to a number of structures where dimers interact via hydrogen bonds. Our computations also reveal a large number of structures where the dominant stabilization arises from C-H···O hydrogen bonds and a smaller set of structures stabilized by purely dispersive interactions between the alkyl chains. Calculated shifts of the stretching O-H frequencies are in very good agreement with experimental values. Energy decomposition analysis shows that the electrostatic term dominates the stabilization of the O-H···O hydrogen bond clusters, while for the other dimers, polarization, charge transfer, and dispersion become the major stabilizing effects.
[Show abstract][Hide abstract] ABSTRACT: The electron delocalization of benzene (C6H6) and hexafluorobenzene (C6F6) was analyzed in terms of the induced magnetic field, nucleus-independent chemical shift (NICS), and ring current strength (RCS). The computed out-of-plane component of the induced magnetic field at a distance (r) greater than or equal to 1.0 Å above the ring center correlates well (R2>0.99) with the RCS value. According to these criteria, fluorination has two effects on the C6 skeleton; concomitantly, the resonant effects diminish the π electron delocalization and the inductive effects decrease the charge density at the ring center and therefore reduce the magnitude of the paratropic current generated in this region. The equilibrium between both effects decreases aromaticity in the fluorinated benzene derivatives. These results can be extrapolated to determine the aromaticity of any derivative within the series of fluorinated benzene derivatives (C6H(6−n)Fn, where n=1-5).
[Show abstract][Hide abstract] ABSTRACT: The potential energy surfaces of a series of clusters with formula CBe5Linn-4 (n=1-5) are systematically explored. Our computations show that the lithium cations preserve the CBe54- pentagon, such that the global minimum structure for these series of clusters has a planar pentacoordinate carbon (ppC). The systems are primarily connected by a network of multicenter σ-bonds, in which C atom acts as σ-acceptor and this acceptance of charge is balanced by the donation of the 2pz electrons to the π-cloud. The induced magnetic field analysis suggests that the clusters with formula CBe5Linn-4 (n=1-5) are fully delocalized. The fact that these ppC-containing clusters are the lowest-energy forms on the corresponding potential energy surfaces raises expectations that these species can be prepared experimentally in the gas phase.
[Show abstract][Hide abstract] ABSTRACT: Extremely complicated isomerization mechanisms for the isomerization of the 2-norbornyl to 1,3-dimethylcyclopentenyl cation observed in the gas phase have been elucidated through Born–Oppenheimer molecular dynamics simulations and ab initio computations. These quantum chemical explorations revealed that there are two viable complex rearrangement pathways. The longer pathway involves consecutive ring-openings with the formation of acyclic allylic cation intermediates. Although these are avoided in the shorter pathway, both routes are feasible, because the energy barriers of their first steps differ by only 1.0 kcal/mol. Both pathways eventually converge to the same methylcyclohexenyl cation, which undergoes ring contraction and methyl and hydride shifts to yield the C11H11+ global minimum, namely the 1,3-dimethylcyclopentenyl cation.
European Journal of Organic Chemistry 12/2014; 2014(35). DOI:10.1002/ejoc.201403146 · 3.07 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ab initio computations are carried out to explore the structure and stability of FNgEF3 and FNgEF (E = Sn, Pb; Ng = Kr-Rn) compounds. They are the first reported systems to possess Ng-Sn and Ng-Pb bonds. Except FKrEF3, the dissociations of FNgSnF3 and FNgEF producing Ng and SnF4 or EF2 are only exergonic in nature at room temperature whereas FNgPbF3 has thermochemical instability with respect to two two-body dissociation channels. However, they are kinetically stable having positive activation barriers (ranging from 2.2 to 49.9 kcal/mol) with respect to those dissociations. The kinetic stability gradually improves in moving from Kr to Rn analogues. The remaining possible dissociation channels for these compounds are found to be endergonic in nature. The nature of bonding is analyzed by natural bond order, electron density, and energy decomposition analyses. Particularly, natural population analysis reveals that they are best represented as F−(NgEF3)+ and F−(NgEF)+. All the Xe/Rn-E bonds in FNgEF3 and FNgEF are covalent in nature.
[Show abstract][Hide abstract] ABSTRACT: Complexity of the potential energy surface of the 9-homocubyl cation is revealed by Born-Oppenheimer molecular dynamics simulations and high ab initio levels. The stereospecific automerizations observed experimentally involve bridged ions, which have either an aromatic or an anti-aromatic character. New pathways leading to more stable isomers are unveiled.
Chemical Communications 11/2014; 51(25). DOI:10.1039/c4cc08071h · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The competence between the possible reaction pathways in the reaction of different cycloalkanes and o-benzyne has been computationally explored. Systems able to undergo complete desaturation by consecutive double hydrogen atom transfer reactions are suggested.
Chemical Communications 10/2014; 51(25). DOI:10.1039/C4CC07311H · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Carbaryl is released into the atmosphere as a spray drift immediately following the application. In order to evaluate its fate in the atmosphere, a computational study on the kinetics of the OH radical reaction with carbaryl is presented. Different reaction paths are studied at the M05-2X/6-311++G(d,p) level. A complex mechanism involving the formation of a stable reactant complex is proposed and the temperature dependence of the rate coefficients is studied in the 280-650 K temperature range. The principal degradation path is the hydroxyl radical addition to naphthalene, but hydrogen abstractions from the methyl group are identified as a secondary significant path. The rate coefficients, computed using the conventional transition state theory, reproduce quite well the scarce experimental data available.
The Journal of Physical Chemistry A 09/2014; 118(36):7776-7781. DOI:10.1021/jp507244s · 2.69 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The global minima of Be2N2, Be3N2 and BeSiN2 clusters are identified using a modified stochastic kick methodology. The structure, stability and bonding nature of these clusters bound to noble gas (Ng) atoms are studied at the MP2/def2-QZVPPD level of theory. Positive BeNg bond dissociation energy, which gradually increases down Group 18 from He to Rn, indicates the bound nature of Ng atoms. All of the Ng-binding processes are exothermic in nature. The Xe and Rn binding to Be2N2 and Be3N2 clusters and ArRn binding to BeSiN2 are exergonic processes at room temperature; however, for the lighter Ng atoms, lower temperatures are needed. Natural population analysis, Wiberg bond index computations, electron density analysis, and energy decomposition analysis are performed to better understand the nature of BeNg bonds.