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The stability, reactivity and aromatic behavior of [Al.sub.7][C.sup.-] and [Al.sub.7][O.sup.-] clusters are analyzed. The site selectivity towards attack by ions and hard/soft electrophiles is studied in terms of atomic charges and philicities.

The mechanism of ground and excited state double proton transfer reaction in formic acid dimer has been analyzed with the help of reaction force and the reaction electronic flux. The separation of reaction electronic flux in terms of electronic activity and reactivity, NBO, and dual descriptor lends additional support for the mechanism. Interestingly we found that the ground state double proton transfer mechanism is concerted synchronic, whereas the excited state double proton transfer is concerted asynchronic in nature. [ABSTRACT FROM AUTHOR]

Alkalimetal cations and halogen anions are well-known componentsof salts. New classes of molecules referred to as superalkalis andsuperhalogens exist whose properties resemble those of alkali andhalogen atoms, respectively. The former have ionization potentialssmaller than those of alkali atoms while the latter have electronaffinities larger than those of halogen atoms. Using gradient-correcteddensity functional theory we have examined the possibility that anew class of salts, referred to as supersalts, could be synthesizedwith superalkalis and superhalogens as building blocks. The possibilitythat hyperhalogens can be synthesized by using superalkalis insteadof alkali atoms as the core has also been examined. Examples of superalkalis(superhalogens) used in this study include Li3O, Cs2Cl, and Cs2NO3(BF4, BeF3, and NO3). While supersalts are found to be stable,the ability of superalkalis to form as the core of hyperhalogens islimited due to their large size. [ABSTRACT FROM AUTHOR]

The mechanism of a simple SN2 reaction, viz;OH–+ CH3F = CH3OH + F–has been studied within the framework of reactionforce and reactionelectronic flux. We have computationally investigated three differenttypes of reaction mechanisms with two different types of transitionstates, leading to two different products. The electronic transfercontribution of the reaction electronic flux was found to play a crucialrole in this reaction. Natural bond order analysis and dual descriptorprovide additional support for elucidating the mechanism of this reaction. [ABSTRACT FROM AUTHOR]

The authors respond to a commentary on their article which proposed an electrophilicity equalization principle. They noted that the proposal was made based on the principles of electronegativity equalization and hardness equalization. They clarified the relevance of density functional theory to their proposed principle.

Superalkalis and superhalogens are atomic clusters that mimic the chemistry of alkali and halogen atoms, respectively; the ionization energies of the superalkalis are less than those of alkali atoms, while the electron affinities of superhalogens are larger than those of the halogen atoms. These superions can serve as the building blocks of a new class of supersalts with applications in solar cells, metal-ion batteries, multiferroic materials, and so on. While considerable progress has been made in the design and synthesis of superhalogens, a similar understanding of superalkalis is lacking. Using density functional theory with hybrid exchange-correlation functional and Gaussian basis sets, we have systematically studied the role of size and composition on the properties of two different classes of clusters whose stabilities are governed by the Wade-Mingos polyhedral skeletal electron pair theory. One class belongs to the closo -borane family Li m B n X n ( m = 1, 2, 3; n = 6, 12; X = H, F, CN), while the other to the Zintl ions Li m [Be@Ge 9 ]. We show that Li 3 B n X n and Li 3 [Be@Ge 9 ] clusters are superalkalis with ionization energies as low as 2.84 eV in Li 3 B 6 H 6 . However, contrary to expectation, the ionization energies do not decrease with increasing cluster volume. Instead, ionization energies are linked to the X ligands' electron affinities; the larger the electron affinity, the higher is the ionization energy. The understanding gained here will help in the discovery of superalkalis and, hence, enrich the library of supersalts.

In quest of a Zintl ion-based Lewis superacids, Al(Ge 9 L 3 ) 3 {L= H, CH 3 , CHO and CN} compounds have been designed and their properties have been studied within the framework of conceptual density functional theory-based reactivity descriptors. Superacid property has been identified for these complexes as per the fluoride ion affinity (FIA) values. Studies reveal that Al[Ge 9 (CN) 3 ] 3 and Al[Ge 9 (CH 3 ) 3 ] 3 behave like superacids as their FIA exceeds the value of SbF 5 , which is considered as the strongest Lewis acid. It has been observed that the ligand plays an important role in reactivity as well as in Lewis acidic property.

Density functional theory (DFT) is one of the popular methods to understand the electronic structure of molecular systems based on electronic density. On the basis of this theory, several conceptual DFT descriptors have been developed which can deal with the stability, reactivity, and several other physicochemical properties of molecules. Here, we have taken a nine-atom-functionalized deltahedral Zintl cluster of germanium (Ge) to examine the alkylation reaction mechanism. The study showed that the Zintl cluster having a methyl group as a ligand, [Ge 9 (CH 3 ) 3 - ], acts as a better nucleophile than the cyanide (-CN)-substituted cluster [Ge 9 (CN) 3 - ] in terms of different thermodynamic parameters like free energy, enthalpy of activation, reaction energy, etc. A detailed reaction electronic flux analysis reveals the nature of the electronic activity throughout the reaction pathway. The reaction force, Wiberg bond indices, and dual descriptor lend additional support to the reaction mechanism. It has been found that the alkylation reaction between the Zintl ion and the alkyl halide follows a S N 2-like mechanism.

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 molecular mechanism of ethanol governed unfolding of an enzymatic protein, chymotrypsin inhibitor 2 (CI2), in water-ethanol mixed solutions has been studied by using combined molecular dynamics simulations and ONIOM study. The residue specific solvation of the unfolded protein and the interactions between the individual amino acid residues of the protein with ethanol as well as water have been investigated. The results are compared with that obtained from the folded state of the protein. Further, emphasis has been given to explore the residue's preferential site of attraction toward the nature of the solvents. The heterogeneous structuring of water and ethanol around the hydrophobic and hydrophilic surfaces of the protein is found to correlate well with their available surface areas to the solvents. Both hydrophobic and hydrophilic interactions are found to have important contributions in rupturing protein's secondary structural segments. Further, residue-water as well as residue-ethanol binding energies show significant involvement of the hydrogen bonding environment in the unfolding process; particularly, residue-water hydrogen bonds are found to play an indispensable role.

A bimetallic 3D network containing 1D chains of Li(6) unit rings has been synthesized by using a molybdenum containing metalloligand and the DFT calculations reveal that the rings are aromatic in behavior and resemble the corresponding hydrocarbon analogues.