NOPR Collection: Special Issue on Chemical Reactivity Theory (Guest Editor: Prof. Pratim Kumar Chattaraj)

Electrostatics and tailoring for aggregation of small linear molecules: An ab initio study

2014-08-08T12:28:11Z

Title: Electrostatics and tailoring for aggregation of small linear molecules: An ab initio study Authors: Singh, Gurmeet; Gadre, Shridhar R Abstract: Features of the molecular electrostatic potential (MESP) for three linear triatomic molecules, viz., CO₂, CS₂ and OCS are utilized for a comparative study of their aggregation into small clusters. Trial structures of clusters upto tetramers, generated by using the MESP insights, are subjected to geometry optimization employing second-order Møller-Plesset (MP2)theory, with correlation consistent aug-cc-pvTZ (aTZ) basis set. Single point energies at MP2/aQZ levels are calculated for the estimation of binding energies at complete basis set (CBS) limit. Calculations at the coupled cluster singles and doubles with perturbative triples (CCSD(T)) level are also reported for the most favorable tetramers using the molecular tailoring approach (MTA). Geometrical parameters such as rotational constants thus obtained are found to be in good agreement with the corresponding experimental ones. Minimal nature of the reported structures is confirmed by the vibrational frequency calculations at MP2/aDZ level of theory. The current work offers some hints towards the patterns in the oligomer formation for these molecules and a comparison of the motifs found in the corresponding crystal structure is made. Page(s): 1019-1030

Quantum information description of reactive systems

2014-08-01T00:00:00Z

Title: Quantum information description of reactive systems Authors: Nalewajski, Roman F Abstract: Information Theory (IT) of molecular electronic states is applied to describe equilibria in separate reactants and reactive system as a whole. It uses the resultant (quantum) measures of the information content in electronic states, determined by both the classical (probability/density) functionals and their non-classical (phase/current)-related complements. The intra-reactant (fragment) equilibrium state in the separate reactant is uniquely characterized by its equilibrium phase related to its own electron distribution, while the inter-reactant (molecular) equilibrium state reflects the stationary electron density of the whole reactive system. The probability currents of the non-bonded reactants, e.g., the isolated fragments or their mutually-closed analogs in the system “promolecular” reference, and of the bonded (mutually-open) fragments in the whole reactive system, are compared to identify the current-promotion of these subsystems. The illustrative case of the two-orbital (2-electron) system is examined in some detail to generate the combination formula for the overall current and to identify its additive and non-additive components. Electron communications between reactants are examined and IT descriptors of the multiplicity and covalent/ionic composition of chemical bonds are related to the additive and non-additive information contributions in local and atomic orbital resolutions. Page(s): 1010-1018

Unraveling the reaction mechanism, enantio and diastereoselectivities of selenium ylide promoted epoxidation

2014-08-08T12:25:43Z

Title: Unraveling the reaction mechanism, enantio and diastereoselectivities of selenium ylide promoted epoxidation Authors: Jaccob, Madhavan; Sabapathi, Gopal; Sundar, J Vijaya; Kolandaivel, P; Subramanian, V; Venuvanalingam, Ponnambalam Abstract: The reaction between chiral selenium ylide and benzaldehyde leads to the formation of (2S,3S)-trans-epoxide with high enantio- and diastereoselectivity. Density functional theory and Hartree-Fock calculations using 6-31G(d) basis set have been performed to understand the reaction mechanism and factors associated with enantio- and diastereoselectivities. Conformation of chiral selenium ylide has been found to have a strong influence on the stability of the initial addition transition state between ylide and benzaldehyde. Calculated enantio- and diastereoselectivities from the energy differences between B3LYP/6-31G(d) addition TSs are in good agreement with the experimental data. The rate and diastereoselectivity are controlled by the cisoid-transoid rotational transition state. Analysis of transition state geometries clearly reveals that unfavorable eclipsing interaction between phenyl groups of the benzaldehyde and ylidic substituents mainly governs the energy differences between the enantio and diastereomeric transition states. The favourable reactivity is also explained through Fukui function calculations. Page(s): 1001-1009

Enhanced interaction of molecular oxygen with amino acid complexes of silver and gold clusters

2014-08-01T00:00:00Z

Title: Enhanced interaction of molecular oxygen with amino acid complexes of silver and gold clusters Authors: Manzoor, Dar; Pal, Sourav Abstract: Density functional theory calculations have been carried out to study the effect of amino acid adsorption on the reactivity of silver and gold clusters with molecular oxygen. It is found that the amino acids glycine and alanine form stable complexes with both Ag₄ and Au₄ clusters. However, the extent of interaction is more in the case of the Au₄ cluster, as reflected from the increase in binding energy in the amino acid Au₄ complexes. Our results confirm that the adsorption of amino acids glycine and alanine enhances the reactivity of Ag₄ and Au₄ clusters towards O₂ molecule. The enhanced reactivity of O₂ molecule towards the amino acid metal cluster complexes is manifested by an increase in the O₂ binding energy and a decrease in the M–O (M = Ag, Au) bond length. Moreover, it is found that the co-adsorption of amino acids and O₂ molecule on the Ag₄ and Au₄ clusters is cooperative. Page(s): 996-1000