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Recently, astronomically important silaisocyanoacetylene (HCCNSi) possessing a large dipole moment has been detected for the first time with the help of crossed molecular beam experiments. Quantum chemical computations at higher levels of theory have also been performed to characterize the transient species. In this study, we have analyzed the equilibrium geometry, stability, reactivity, and energetics as well as the nature of bonding in the noble gas (Ng) inserted HCCNSi compound. We have also considered its F analogue to understand the influence of the most electronegative atom in the compound. Metastable behavior of the XNgNSi compounds (X = HCC, F; Ng = Kr-Rn) is examined by calculating thermochemical parameters like free energy change (ΔG) and zero-point-energy-corrected dissociation energy (D0) at 298 K for all possible two-body (2B) and three-body (3B) (both neutral as well as ionic) dissociation channels using coupled-cluster theory [CCSD(T)] in addition to density functional theory (DFT) as well as second order Moller-Plesset perturbation theory (MP2). The set of predicted compounds is found to be endergonic in nature, having high positive free energy change suggesting the thermochemical stability of the compounds except for the 2B Ng-release paths. Though thermodynamically feasible, they are kinetically protected with very high activation free energy barriers. Interestingly, the release of Ng from the parent moiety XNgNSi produces the XSiN isomer, by 180° flipping of the NSi moiety. This can also be seen in the dynamical simulation carried out with the help of atom-centered density matrix propagation (ADMP) technique at 2000K for 1 ps. The bonding in Ng-C, Ng-F, and Ng-N bonds of the studied compounds is analyzed and described with the aid of natural bond orbital (NBO), topological parameters computed using atoms-in-molecules theory (AIM), energy decomposition analysis (EDA), and adaptive natural density partitioning (AdNDP) methods. The natural charge distribution on the constituent atoms suggests that the compounds can be partitioned into both ways of representations, viz., neutral radical as well as ionic fragments. Lastly, the reactivity of the compounds is scrutinized using certain reactivity descriptors calculated within the domain of conceptual density functional theory (CDFT).

Atomic clusters are unique in many perspectives because of their size and structure features and are continuously being applied for different purposes. To unveil their unconventional properties, in this work, using neutral tetraboron clusters as illustrative examples, we study their exotic behaviors in bonding, aromaticity, and reactivity. We show that both double and triple bonds can be formed, ring current patterns can be totally different, and both electrophilic and nucleophilic reactivities can coexist simultaneously. These features are often in contrast with our conventional chemical wisdom and could enrich the possibility for their potential applications. The methodologies employed in this work can be readily applied to other systems. Our studies should help us better appreciate atomic clusters with many atypical properties and henceforth yield novel applications.

The cycloaddition of ethylene, cyanoethylene, and propylene to a five-membered P/B frustrated Lewis pair (FLP) is shown to be highly favorable under normal conditions, as confirmed by the computed thermodynamic and kinetic data. All of these cycloaddition reactions are concerted as highlighted by the intrinsic reaction coordinate (IRC) and Wiberg bond index calculations. Almost 70% of the reaction force is required for structural orientation to initiate electronic activity. The reactions are interpreted by the frontier molecular orbital (FMO) analysis and conceptual density functional theory (DFT)-based reactivity descriptors. It appears that ethylene and propylene will act as nucleophiles, while the FLP will act as an electrophile throughout the cycloaddition reaction, however, cyanoethylene will act as an electrophile and the FLP as a nucleophile. Regioselectivities of the cycloadditon of cyanoethylene and propylene to the FLP are further verified through philicity and dual descriptors. It is demonstrated that an FLP can be forced to act as an electrophile or a nucleophile by intelligently selecting its partner in a cycloaddition reaction. Even the P and B centers would behave differently within the same FLP. This strategy may be properly exploited by the experimentalists in designing a suitable reaction for the synthesis of any useful molecule possessing the desired property.

The scientific community is engrossed in the thought of a probable solution to the future energy crisis keeping in mind a better environment-friendly alternative. Although there are many such alternatives, the green hydrogen energy has occupied most of the brilliant minds due to its abundance and numerous production resources. For the advancement of hydrogen economy, Government agencies are funding pertinent research projects. There is an avalanche of molecular systems which are studied by several chemists for storing atomic and molecular hydrogens. The present review on molecular hydrogen storage focuses on all-metal and nonmetal aromatic clusters. In addition to the effect of aromaticity on hydrogen trapping potential of different molecular moieties, the importance of using the conceptual density functional theory based reactivity descriptors is also highlighted. Investigations from our group have been revealing the fact that several aromatic metal clusters, metal doped nonmetal clusters as well as pure nonmetal clusters can serve as potential molecular hydrogen trapping agents. Reported systems include N4Li2, N6Ca2 clusters, Mgn, and Can (n = 8–10) cage-like moieties, B12N12 clathrate, transition metal doped ethylene complexes, M3+ (M = Li, Na) ions, E3-M2 (E = Be, Mg, Al; M = Li, Na, K) clusters, Li3Al4− ions, Li decorated star-like molecules, BxLiy (x = 3–6; y = 1, 2), Li-doped annular forms, Li-doped borazine derivatives, C12N12 clusters (N4C3H)6Li6 and associated 3-D functional material, cucurbiturils, lithium–phosphorus double-helices. Ni bound C12N12 moieties are also reported recently.

Atomic clusters lie somewhere in between isolated atoms and extended solids with distinctly different reactivity patterns. They are known to be useful as catalysts facilitating several reactions of industrial importance. Various machine learning based techniques have been adopted in generating their global minimum energy structures. Bond-stretch isomerism, aromatic stabilization, Rener-Teller effect, improved superhalogen/superalkali properties, and electride characteristics are some of the hallmarks of these clusters. Different all-metal and nonmetal clusters exhibit a variety of aromatic characteristics. Some of these clusters are dynamically stable as exemplified through their fluxional behavior. Several of these cluster cavitands are found to be agents for effective confinement. The confined media cause drastic changes in bonding, reactivity, and other properties, for example, bonding between two noble gas atoms, and remarkable acceleration in the rate of a chemical reaction under confinement. They have potential to be good hydrogen storage materials and also to activate small molecules for various purposes. Many atomic clusters show exceptional opto-electronic, magnetic, and nonlinear optical properties. In this Review article, we intend to highlight all these aspects.

Using the electron density and its associated quantities in a molecular system to quantify chemical reactivity in density functional theory is of considerable recent interest. Local temperature based on the kinetic energy density is an intrinsic property of a molecular system, which can be employed for this purpose. In this work, we explore such a possibility. To this end, we examine the local behavior of local temperature with a few choices of the kinetic energy density, apply it to determine regioselectivity of nucleophilic and electrophilic compounds, and then investigate its performance in appreciating reactions along the intrinsic reaction pathway for exothermic, endothermic, and thermoneutral transformations. Our results confirm that local temperature can be used as an effective descriptor of molecular reactivity.

Confinement causes drastic changes in bonding, reactivity and dynamics. Alkali metal atoms are excellent reducing agents due to their low ionization energies. On the other hand, high electron affinity values allow the halogen atoms to behave as powerful oxidizing agents. In this article, we have shown that those properties get changed in a confined environment created by two fullerenes differing in size.

Aromaticity indices are defined in terms of the conceptual density functional theory-based reactivity descriptors and the associated electronic structure principles. In this chapter, the aromatic/antiaromatic nature of various illustrative systems is assessed by using these indices.

Although the toxicity of beryllium compounds causes impediments in experiments involving them, beryllium chemistry has seen a recent upsurge of interest and considerable progress. Computations play a very important complementary role in analyzing the structure, stability and bonding of these compounds. In this perspective article, we highlighted our contribution to beryllium chemistry which is either completely through theoretical results or sometimes supported by experimental findings. It starts with the smallest 2π aromatic system, Be32-, which also exhibits rare bond-stretch isomerism. Furthermore, its reactivity towards different transformations is mentioned. Because of the ability of beryllium to attain a high ionic potential, the beryllium center in an appropriate situation can act as an excellent Lewis acid which is utilized to bind noble gas (Ng) atoms, carbon monoxide and dinitrogen through donor-acceptor types of interactions. We made several efforts to have strong Ng-Be bonds which led us to NgBeNCN that is recorded to have the strongest Ng-Be bond among the neutral Ng-Be complexes reported so far. Significant dinitrogen activation was also achieved in (NN)2Be(η2-N2) and OCBeNN complexes. In the latter case, a complete cleavage of the N-N bond producing the most stable NBeNCO molecule has occurred. We also found viable M2(NHBMe)2 (M = Be, Mg) complexes having unusual bonding where the interacting fragments are best described as the neutral M2 and (NHBMe)2 but M2 still possesses a single bond. We finally discussed the complex comprising an unusual Be(i) oxidation state, [BeI(cAACAr)2]+˙ and di-ortho-beryllated carbodiphosphorane exhibiting Be⇇C double dative bonds.

Noble gas can be no noble in certain situations from the perspective of structure, bonding, and reactivity. These situations could be extreme experimental conditions or others. In this contribution, we systematically investigate the impact of fullerene encapsulation on molecular structure and chemical reactivity of noble gas dimers (Ng2) in a few fullerene molecules. To that end, we consider He2, Ne2, and Ar2 dimers encapsulated in C50, C60, and C70 fullerenes. We unveil that bond distances of Ng2 inside fullerene become substantially smaller and noble gas atoms become more electrophilic. In return, these noble gas dimers make fullerene molecules more nucleophilic. Using analytical tools from density functional theory, conceptual density functional theory, and information-theoretic approach, we appreciate the nature and origin of these structure and reactivity changes. The results and conclusions from this work should provide more new insights from the viewpoint of changing the perspectives of noble gas reactivity.

Chemical reactivity properties such as regioselectivity, electrophilicity and nucleophilicity are important chemical concepts, yet their understanding and quantification are still far from being accomplished. Applying density functional theory (DFT) to appreciate these properties is one route to pursue in the literature. In this work, we present a comparative study to benchmark two approaches in DFT to predict regioselectivity, electrophilicity and nucleophilicity: one with the Hirshfeld charge and the other with the Fukui function. We also examine the impact of 15 different ways to compute atomic charges on the performance of their predictions about these chemical reactivity properties. Our results show that the Hirshfeld charge is able to reliably determine regioselectivity and simultaneously accurately quantify both electrophilicity and nucleophilicity. The Fukui function behaves reasonably well for the prediction of electrophilicity but performs poorly for nucleophilicity. Among all other atomic charges examined in this study, it is only the Voronoi deformation density charge that yields the similar result as the Hirshfeld charge. As the first systematic benchmark study in the literature to compare the two available approaches in DFT about reactivity predictions, this work should fill in the needed knowledge gap and provide an impetus for the future development of chemical reactivity theory using DFT language.

Within the context of quantum fluid density functional theory diverse processes simulating a chemical reaction like interaction of an atom or a molecule with an externally applied electric or magnetic field or its collision with a proton have been analyzed in a dynamical situation. The changes produced in the chemical reactivity parameters namely chemical potential, hardness, polarizability during such processes have been identified and discussed. In addition, confinement is also introduced to observe the necessary variation in the different reactivity parameters.

Chemical reactivity is discussed in terms of various conceptual density functional theory based global and local reactivity descriptors like electronegativity, chemical hardness and softness (and their local variants), chemical potential, polarizability, Fukui functions, and local philicity. The behaviour of these parameters for different molecular systems and processes is explained using various principles associated with the electronic structure theory.

An in silico analysis is performed to check the hydrogen storage potential of (HF)m (m = 1–8) and (H2O)n (n = 1–10) clusters. Each HF unit in (HF)m cluster can bind three H2 molecules whereas each H2O unit in (H2O)n can adsorb one hydrogen molecule (excluding H2O and (H2O)2). It is found that conceptual density functional theory based reactivity descriptors can explain the stability of molecular hydrogen adsorbed (HF)m (m = 1–8) and (H2O)n (n = 1–10) clusters. The nature of interaction between (HF)m/(H2O)n cluster and the adsorbed H2 molecules is studied using electron density based descriptors. Energy decomposition analysis is carried out to assess the type of interaction between the molecular clusters and adsorbed hydrogen molecules. Ab initio molecular dynamics (AIMD) simulation is also carried out using an atom centered density matrix propagation (ADMP) technique to predict the kinetic stability of hydrogen adsorbed (HF)m and (H2O)n analogues in a one picosecond time scale.

Although aromaticity is widely used in explaining the “extra stability” of a particular class of organic compounds, it has not been properly defined. It is subsequently extended to several other systems including inorganic and all-metal systems. Hence, an aromatic moiety with extraordinary stability can act as a promising building block for various nanomaterials. In this chapter, we present aromaticity in various all-metal and nonmetal systems, and the hydrogen (H2) storage potential of different novel molecular templates composed of aromatic units. A thorough analysis is carried out to understand the effect of H2 binding on the aromaticity of the template and vice versa. Whereas aromaticity is assessed through the study of various energetic, geometrical, magnetic, and reactivity criteria, H2 binding ability is evaluated by computing the related binding energy. The construction of temperature–pressure (T–P) phase diagrams for various systems highlights T–P regions where the adsorption or desorption of H2 would be favorable. Furthermore, the effect of an external electric field on improving the H2 binding ability of a template is explored.

The interaction of BN- and BP-doped graphene nanoflakes with some representative neutral molecules and anions (H2O, HF, SH−, CH3O−, BO2−, F−) has been studied through density functional theory (DFT) calculations. The neutral molecules remain physisorbed whereas all the anions but one remains chemisorbed. Thermodynamically, most of the studied systems are found to be stable. Conceptual DFT-based reactivity descriptors were employed in order to provide rationale behind such observation. The nature of interactions in cases of the anions is predominantly of covalent type whereas the same for neutral molecules is of non-covalent type. The electrostatic and orbital interactions play important roles in stabilising the absorbed moieties. The kinetic stability of the absorbed moieties is confirmed through an atom-centred density matrix propagation simulation at 298 K temperature up to 500 fs. All the studied systems show excellent kinetic stability and remain absorbed up to 500 fs exhibiting rich vibrational and r...

The validity of maximum hardness, minimum electrophilicity and minimum polarizability principles is assessed to explain the phenomenon of torquoselectivity (inward and outward preference) in the conrotatory ring opening reactions of trans-3,4-dimethylcyclobutene into Z,Z- and E,E-butadienes and 3-formylcyclobutene into E- and Z-2,4-pentadienals. The hardness, average polarizability and electrophilicity profiles are computed along the intrinsic reaction coordinate and divided into three relevant stages. The transition states involved in the unfavorable inward conrotation of trans-3,4-dimethylcyclobutene and in the unfavorable outward conrotation of 3-formylcyclobutene are found to be higher in energy, softer, more electrophilic and more polarizable than the transition states corresponding to the torquoselective outward and inward conrotations, respectively. These observations are in conformity with the maximum hardness, minimum electrophilicity and minimum polarizability principles. The sharp changes in the local reactivity descriptors are also observed around the transition states in their respective profiles.

Developing effective structure-activity/property/toxicity relationships (QSAR/QSPR/QSTR) is very helpful in predicting biological activity, property, and toxicity of a given set of molecules. Regular change in these properties with the structural alteration is the main reason to obtain QSAR/QSPR/QSTR models. The advancement in making different QSAR/QSPR/QSTR models to describe activity, property, and toxicity of various groups of molecules is reviewed in this chapter. The successful implementation of Conceptual Density Functional Theory (CDFT)-based global as well as local reactivity descriptors in modeling effective QSAR/QSPR/QSTR is highlighted.

The reactivity descriptors like electronegativity, hardness, and electrophilicity, formulated on conceptual density functional theory can explain chemical reactivity of various acids and bases, oxidants and reductants as well as electrophiles and nucleophiles through associated structure-stability diagrams. © 2014 Wiley Periodicals, Inc.

Prompted by a recent Letter (Brito et al., 2013) [9], stability and dynamics of the cyclic and linear Be 3 2 - clusters are studied. CASSCF is used over coupled cluster and other single reference methods on the basis of T1 diagnostic. Ab initio molecular dynamics (ADMP) study reveals the fate of cyclic and linear Be 3 2 - clusters up to 3.25 ps. Total energy and conceptual density functional theory based reactivity descriptors, hardness and electrophilicity vary with time during simulation. Energy, hardness and electrophilicity trajectories help to understand the structural dynamics of Be 3 2 - clusters.

A distinctive N-substituent controlled electrophilic N-transfer of oxaziridines with donor–acceptor cyclopropanes in the presence of MgI2 is reported. Contrary to earlier reports, the oxaziridine having bulkier N-substituents can also give N-transferred product instead of the O-transferred one. Interestingly, the oxaziridines having α-H containing N-substituents lead to the pyrrolidine derivatives through [3 + 2] cycloaddition. A mechanistic reasoning for this divergent reactivity is depicted by density functional theory calculations and validated through energy decomposition analysis.

The efficacy of different conceptual density functional theory based reactivity descriptors and nucleus independent chemical shift in analyzing the hydrogen trapping potential of a wide variety of systems is reviewed in this chapter. The influence of aromaticity on the stability/reactivity of hydrogen storage material as well as structural and bonding aspects of those materials are explored. Charges on the different active sites in a molecule play a crucial role in their hydrogen-trapping ability. Temperature−pressure diagrams highlighting the ΔG

The fundamental principles of pericyclic reactions are governed by the Woodward-Hoffmann rules, which state that these reactions can only take place if the symmetries of the reactants' molecular orbitals and the products' molecular orbitals are the same. As such, these rules rely on the nodal structure of either the wave function or the frontier molecular orbitals, so it is unclear how these rules can be recovered in the density functional reactivity theory (or "conceptual DFT"), where the basic quantity is the strictly positive electron density. A third, nonsymmetry based approach to predict the outcome of pericyclic reactions is due to Zimmerman which uses the concept of the aromatic transition states: allowed reactions possess aromatic transition states, while forbidden reactions possess antiaromatic transition states. Based on our recent work on cycloadditions, we investigate the initial response of the chemical hardness, a central DFT based reactivity index, along the reaction profiles of a series of electrocyclizations. For a number of cases, we also compute complete initial reaction coordinate (IRC) paths and hardness profiles. We find that the hardness response is always higher for the allowed modes than for the forbidden modes. This suggests that the initial hardness response along the IRC is the key for casting the Woodward-Hoffmann rules into conceptual DFT.

The ability of neutral and cationic BxLiy (x = 2–6; y = 1, 2) systems as effective hydrogen-trapping materials are investigated at the MP2 level of theory using the 6-311+G(d, p) basis set. The different conceptual DFT-based global and local reactivity descriptors and the associated electronic structure principles provide invaluable insights toward assessing the utility of the boron–lithium clusters in trapping molecular hydrogen. A consistent thermodynamic spontaneity of the allied H2-binding reactions along with a favorable decrease in the average dissociative chemisorption energies invokes the plausible usage of these cluster motifs for hydrogen loading in practice. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Hydrogen trapping ability of various metal–ethylene complexes has been studied at the B3LYP and MP2 levels of theory using the 6-311+G(d,p) basis set. Different global and local reactivity descriptors and the associated electronic structure principles provide important insights into the associated interactions. There exist two distinct classes of bonding patterns, viz., a Kubas type interaction between the metal and the H2 molecule behaving as a η2-ligand and an electrostatic interaction between the metal and the atomic hydrogens.

Geometries of different isomers of various neutral sulfur clusters, S n (n=3–8) are optimized at the B3LYP/6-311+G* level of theory. Their stability and aromaticity behavior are analyzed in terms of the conceptual density functional theory-based reactivity descriptors and the associated electronic structure principles. The nucleus-independent chemical shift lends additional support. Possibility of bond-stretch isomerism in these clusters is explored.

Geometries of several all-metal clusters with Zn32− as the base are optimized within a B3LYP/6-311+G(d) level of theory. It is analyzed that the stability, bonding, reactivity and aromaticity patterns of such clusters often change drastically in the presence of counter cations like Li+, Na+ or K+ and/or through the substitution of Zn32− units by Be5− or C5H5− rings.

To understand the source of discrepancy in the qualitative trends in the reactivity of the spherically confined atoms/ions when the high pressure is generated through the use of a proper Dirichlet boundary condition [J. Chem. Sci. 2005, 117, 379; Phys. Chem. Chem. Phys. 2008, 10, 1406] and of a cutoff function [Chem. Phys. Lett. 2003, 372, 805; J. Phys. Chem. A 2003, 107, 4877], a modified Herman-Skilman program is run. Results obtained from different formulas of reactivity parameters are analyzed. Change in reactivity for different electronic configurations is also reported. It is observed that the use of different formulas is the major source of discrepancy and not the Dirichlet condition, although the latter is highly recommended. As the cutoff radius of the confining spherical box decreases, the energy of the atom/ion increases, the electronegativity decreases, and the hardness increases and ultimately slightly decreases in an ultraconfined situation. For small R(C) values, softness decreases and electrophilicity increases and attains relatively small values. The reactivity of confined atoms/ions is put in a proper perspective.

Several sandwich-like metal clusters have been studied at the B3LYP/6-311 + G* level of theory. Bonding and reactivity have been analysed through various geometrical parameters and conceptual density functional theory based global reactivity descriptors. Aromaticity patterns have been understood in terms of the associated nucleus independent chemical shift values. Possibility of bond-stretch isomerism in some doped clusters is explored. Preferable sites for electrophilic and nucleophilic attacks have been identified using different local reactivity descriptors.

Global and local reactivity descriptors as well as the nucleus independent chemical shift values of different multi-decker sandwich complexes involving Be32− and Mg32− dianions are calculated at the B3LYP/6-311+G level of theory. Important insights into their bonding, reactivity, and aromaticity are obtained through this study.

Changes in the bonding, aromaticity and reactivity behavior associated with the following reaction cycle including all the intermediate steps are studied at the B3LYP/6-311+G(d) level of theory: Various sandwich-like complexes studied here may be synthesized and used for different purposes such as catalysis and molecular electronics.

A two-step substitution reaction: CpZnZnCp ( D 5 h ) → - 2 Cp - + 2 Be 3 2 - [ Be 3 ZnZnBe 3 ] 2 - ( D 3 h ) → - 2 Zn + + 2 Be + [ Be 3 BeBeBe 3 ] 2 - ( D 3 h ) is studied at the B3LYP/6-311+G[d] level of theory. The resulting all-beryllium sandwich-like complex, Be 8 2 - is highly stable and aromatic. The ring-Be atoms show different reactivity towards hard and soft electro (nucleo) philes than the bond-Be atoms.

A new polydentate fac-trioxo molybdenum complex, [MoO$_{3}$L]$^{2-}$ {L=iminodiacetate} has been synthesized by the reaction of sodium molybdate and iminodiacetic acid. The dinegative complex anion acts as a ligand towards alkali metal cations, Na$^{+}$. The sodium complex, [Na$_{2}$MoO$_{3}$L(H$_{2}$O)$_{2}$]$_{n}$ (1) is a 3D hereto bimetallic coordination polymer, containing a unique hexagonal 1D sodium cluster chain. The DFT calculations on hexagonal sodium cluster show that, the (Na$_{6)$ rings in the chain are highly aromatic in character and the NICS (0) values of the Na$_{6}$ rings are almost same as their polyacene analogues. The stability and reactivity pattern of the Na$_{6}$ rings also follow the same pattern as their organic analogues. Related analysis on Li-cluster is also accomplished. A theoretical investigation based on DFT is performed to find out the possible stable structures of Li$_{6}$, Na$_{6}$, K$_{6}$, Li$_{3}$Na$_{3}$ and Na$_{3}$K$_{3}$ molecules and a common D$_{3h}$ symmetric structure is found. Also the reactions between Li$_{6}$ and Na$_{6}$ as well as Na$_{6}$ and K$_{6}$ are found to be thermodynamically favourable. Importance of the presence of the metalloligand in inducting the aromatic behaviour is highlighted.

Some representative chemical reactions and all-metal aromatic/antiaromatic compounds are studied ab initio in order to understand the efficacy of the multicenter indices in providing insights into the associated bonding, reactivity and aromaticity. It is observed that the said indices serve the purpose in most cases.

The stability, reactivity, and aromaticity of the Be32- dianion and its bimetallic species are investigated. The aromaticity of these systems is analyzed in the light of the DFT-based reactivity descriptors, namely, hardness (eta) and polarizability (alpha), molecular orbital (MO) analysis, and the nucleus-independent chemical shift (NICS). The recently discovered direct Zn-Zn bond is stabilized through the complexation with Be32-, and a new compound [(Be3)2Zn2]2- is reported. The chemical nature and selectivity of the Be32- unit in its bimetallic form are analyzed using the atomic charge (Qk) and nucleophilicity excess (Deltaomega++g) descriptors to examine its applicability in the field of molecular electronics.

Various electronic structure principles are analyzed in time-independent and time-dependent situations. Periodicity and chemical reactions have been studied as representative static cases. A generalized nonlinear Schrodinger equation has been solved in gaining insights into the reactivity dynamics associated with ion-atom collisions and atom-field interactions. Dynamical variants of various electronic structure principles reveal themselves.

We present a systematic density functional theory study of the global and local reactivity patterns of [n]paracyclophanes. Maximum hardness principle (MHP) and minimum electrophilicity principle (MEP) are obeyed in these strained molecules. Linear relationships among strain energy, electrophilicity, aromatic stabilization energy and chemical hardness are established. The Fukui function (FF) values at the carbon atoms of the benzene ring of [n]paracyclophanes are critically analyzed. The presence of weak C-H...π interactions is evident from the AIM topographical analysis.

Density functional theory and ab initio molecular orbital calculations have been carried out in order to get insights into the structure, chemical reactivity and property information for the series of chloroanisoles. Descriptors such as energy, hardness, chemical potential, electrophilicity index and polarizability provide vital information about the global reactivity of chloroanisoles. Further, we utilized our recently proposed multiphilic descriptor defined as the difference between nucleophilic and electrophilic condensed philicity functions to understand the local reactivity/site selectivity on the series of chloroanisoles. Also, structure-property relationship in chloroanisoles shows the importance of the electrophilicity index in the property prediction.

The environmental effects of chloroanilines depend on their physical and chemical properties, and it is therefore important to know their structure-property relationships that allow a complete understanding of their environmental consequences. The chemical reactivity profiles of all 19 chloroanilines have been investigated using the density functional theory for the first time. Global reactivity descriptors, such as hardness, chemical potential, electrophilicity index, and polarizability, and local reactivity descriptors, namely, local philicities, have been calculated in order to gain insights into the reactive nature and the reactive sites of the selected systems. Using AIM theory, the presence of hydrogen bond critical points (HBCPs) and the values of electron density and Laplacian of electron density at the HBCPs have been analyzed to appreciate the presence of intramolecular hydrogen bonding in the selected systems. Structure-toxicity analysis of the selected set of chloroanilines demonstrates the importance of the electrophilicity index in the prediction of reactivity/toxicity.

The structure and chemical reactivity profiles of all 12 chlorobenzenes have been investigated using the density functional theory and ab initio molecular orbital calculations. Global and local reactivity descriptors such as electrophilicity index and local philicity, respectively, of the selected systems have been calculated in order to gain insights into the reactive nature and the reactive sites of these compounds. Also, the effects of chlorine substitution on the aromaticity of the compounds have been analyzed by calculating the nucleus-independent chemical shift. Interaction through charge transfer between chlorobenzenes and nucleic acid bases/selected base pairs are determined using Parr's formula. The results revealed that the chlorobenzenes act as electron acceptors in their interaction with biomolecules. Structure-toxicity analysis of this entire set of chlorobenzenes demonstrates the importance of the electrophilicity index in the prediction of reactivity/toxicity.

Cracking of n-heptane in HZSM-5 zeolite is studied through generalized gradient approximation mediated single point calculations at the BLYP-DZVP level on the extremal points of a corresponding quantum molecular dynamics simulation carried out at 800 K using the same level of theory. The global reactivity descriptors like electronegativity, hardness and electrophilicity are important in understanding the reaction mechanism in terms of the stabilities and reactivities of various species involved. Different centers become reactive towards electrophilic and nucleophilic attacks during the process of hydrocarbon cleavage and local reactivity descriptors adequately take care of that.

The toxicity of 33′44′55′-hexa chlorobiphenyl (HCBP), a non-ortho substituted polychlorinated biphenyl (PCB) is analyzed using the rotational energy barrier as well as some conceptual density functional theory (DFT) based global and local reactivity descriptors. The flexibility of the molecule is evident from the low value of rotational barrier height. The profiles of global reactivity descriptors and relative energy clearly demonstrate the overall toxic nature whereas the local descriptors provide information about the probable reactive sites of HCBP. The partial charge transfer during the interaction between HCBP and DNA bases/selected base pairs is also computed using Parr's formula. The flexibility and the electron accepting nature of HCBP are shown to be the dominant factors of its toxicity.

The applicability of DFT -based descriptors for the development of toxicological structure - activity relationships is assessed. Emphasis in the present study is on the quality of DFT -based descrip- tors for the development of toxicological QSARs and, more specifically, on the potential of the electrophili - city concept in predicting toxicity of benzidine derivatives and the series of polyaromatic hydrocarbons (PAH) expressed in terms of their biological activity data ( pIC50). First, two benzidine deriv atives, which act as electron -donating agents in their interactions with biomolecules are considered. Overall toxicity in general and the most probable site of reactivity in particular are effectively described by the global and local electrophilicity parameters re spectively. Interaction of two benzidine derivatives with nucleic acid (NA) bases/selected base pairs is determined using Parr's charge transfer formula. The experimental bi o- logical activity data ( pIC50) for the family of PAH, namely polychlorinated dibenz ofurans (PCDF), poly- halogenated dibenzo-p-dioxins (PHDD) and polychlorinated biphenyls (PCB) are taken as dependent variables and the HF energy (E), along with DFT-based global and local descriptors, viz., electrophilicity index (ω) and local electrophilic power (ω + ) respectively are taken as independent var iables. Fairly good correlation is obtained showing the significance of the selected descriptors in the QSAR on toxins that act as electron acceptors in the presence of biomolecules. Effects of populatio n analysis schemes in the cal- culation of Fukui functions as well as that of solvation are probed. Similarly, some electron -donor ali- phatic amines are studied in the present work. We see that global and local ele ctrophilicities along with the HF energy are adequate in explaining the toxicity of several substances, both electron donors or a c- ceptors when they interact with biosystems, in gas as well as solution phases.

Adsorption of small molecules like CH4, CO and NH3 into the acid sites of zeolites is analysed as an interaction between an electrophile and a nucleophile. Global reactivity descriptors like softness and electrophilicity, and local reactivity descriptors like the Fukui function, local softness and local philicity are calculated within density functional as well as Hartree-Fock frameworks using both Mulliken and Hirshfeld population analysis schemes. The HSAB principle and the best electrophile-nucleophile combination suggest that the reaction between the NH3 and Bronsted acid site of the zeolite is the strongest. Interaction between the zeolite and a small probe molecule takes place through the most electrophilic atom of one with the most nucleophilic atom of the other. This result is in conformity with those provided by the frontier orbital theory and the local HSAB principle.

The interrelationships between global reactivity descriptors such as chemical hardness, chemical potential, polarizability and electrophilicity and associated electronic structure principles were investigated in detail by considering distortion along the normal coordinates from the equilibrium structure and internal rotation. The necessary conditions on the extremum of electrophilicity were probed along with other electronic structure principles associated with the global reactivity descriptors. It was observed that an extremum in electrophilicity is obtained where both chemical potential and chemical hardness attain their respective exiremal values in course of the molecular vibrations as well as internal rotations.

Variation of global reactivity descriptors along the two different pathways for formaldehyde decomposition has been investigated in order to analyze the validity of various electronic structure principles of density functional theory. Calculated energetics and geometrical parameters are in good agreement with the previous investigations. The hardness and electrophilicity are, respectively, found to be a pointer of the most stable and the most reactive identity in most cases. Profiles of these quantities, as a function of the reaction coordinates narrate the dependability of the descriptors. The difference in the global reactivity descriptors between a symmetric reaction and a non-symmetrical reaction along the reaction coordinate in the same decomposition pathway has also been analyzed. Our investigation provides useful exploratory guidelines towards the foundation of chemical reactivity descriptors.

An attempt has been made to test the usefulness of the generalized philicity concept of Chattaraj et al. through gas- and solution-phase density functional theory calculations on some aliphatic amines. Local philicity provides important clues about the reactivity and selectivity, and it contains almost all the known global and local chemical reactivity parameters. Local philicity provides the Fukui function, but the converse is not true. We have also studied the effect of solvent (water) on reactivity. The philicities are in general less in solvent than in the gas phase, but the total energy and dipole moment are higher in the solvent medium.