Silabenzene through divalent precursors at theoretical levels

Abstract  Based on geometries and relative energies, three different mechanisms are proposed for the rearrangements of five isomers of silacyclohexadienylidenes to silabenzene at B3LYP and MP2 levels: (1) [1,2]-hydrogen migration through a planar transition state, (2) [1,4]-hydrogen migration through a boat transition state, and (3) zip-zap mechanism, comprised of three successive [1,2]-hydrogen migrations. The above results are compared and contrasted to rearrangements of the corresponding cyclohexadienylidenes to benzene. Graphical abstract   Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

A DFT study on pyridine-derived N-heterocyclic carbenes

To appreciate the chemistry of N-heterocyclic carbenes (NHCs), eight carbenic tautomers of pyridine (azacyclohexadienylidenes) are studied at B3LYP/AUG-cc-pVTZ//B3LYP/6-31+G^∗ and B3LYP/6-311++G^∗∗//B3LYP/6-31+G^∗ levels of theory. Various thermodynamic parameters are calculated for these minima, along with a kinetic focus on carbene-pyridine tautomerization. Appropriate isodesmic reactions show stabilization energies of 2-azacyclohexa-3,5-dienylidene (1) and 4-azacyclohexa-2,5-dienylidene (6) as 119.4 and 104.1 kcal/mol, rather close to that of the synthesized 1,3-dimethylimidazol-2-ylidene (129.2 kcal/mol). Three different mechanisms are suggested for the tautomerizations including: [1,2]-H shift, [1,4]-H shift, and three sequential [1,2]-H shifts. The calculated energy barrier for [1,2]-H shift of 1 is 44.6 kcal/mol, while the first [1,2]-H shift for the proposed sequential mechanism of 6 requires 65.1 kcal/mol. Three preliminary minimum templates are introduced, which may possess the potential of synthetic consideration: 2,6-di(X)-3,5-dichloro-4-azacyclohexa-2,5-dienylidene for X=Mes, t-Bu, and Ad.     

Detection of bendamustine anti-cancer drug via AlN and Si-doped C nanocone and nanosheet sensors by DFT

Bendamustine or Treanda? is used as an anti-cancer drug, especially in treatment of hematologic malignancies. In view of the immense importance of drug/sensor issues, here we report adsorption behavior of this drug in presence of six nanosensors including aluminum nitride (AlN), carbon, and Si-doped carbon nanocones and nanosheets, at B3LYP/6-31G* level of theory. Electrical conductivity of these nanoadsorbents is probed against that of bendamustine for assessing their abilities of drug sensing with possible implications in drug delivery. The adsorption energy (E_ad), doping energy (E_dop), HOMO energy (E_H), LUMO energy (E_L), HOMO-LUMO band gap (E_g), change of band gaps in percent (%?E_g), change of natural bond orbital (NBO) charges (?Q), conduction electron population (N), and density of state (DOS) plots are calculated. More E_ad, ?Q, and N values imply more interaction between bendamustine and nanosensor which lead to a strong recognition of the drug. The interaction of AlN nanosheet and bendamustine shows the highest E_ad, %?E_g, and ?Q (??28.8 kcal/mol, ??33.6%, and 0.4 e, respectively) which make AlN nanosheet as the most promising among our scrutinized nanosensors. A negative E_dop indicates an exothermic doping process, where Si atom improves the electronic sensitivity of C nanocone and nanosheet. All calculated E_ad and %?E_g turn out as negative values which reveal that electrical conductivity of our scrutinized nanostructures are increased upon adsorbing process which makes them efficient sensors for bendamustine.

Graphical abstract

     

Synthesis of 2,4,5‐trisubstituted imidazoles over reusable CoFe2O4 nanoparticles: an efficient and green sonochemical process

Numerous reports of the synthesis of 2,4,5‐trisubstituted imidazoles demonstrate their significance as biologically important molecules. Here we carried out their fast and efficient one‐step green sonochemical synthesis through condensation of aldehyde, diketone and ammonium acetate, over reusable superparamagnetic CoFe₂O₄ nanoparticles. Copyright © 2016 John Wiley & Sons, Ltd.     

A theoretical quest for graphene nanoribbons: effects of nitrogen substitution on the ground state alteration

Abstract  

The effects of nitrogen substitution on the multiplicity of two sets of [X,Y] graphene nanoribbons, including peri region as well as peri-bay region substituted species, are calculated at B3LYP/6-31G* density functional theory (DFT) level. Such substitution on peri regions of [3,3] and [3,5] nanoribbons increases their viability by altering their ground states from singlet open shell (S_OS) to singlet closed shell (S_CS). This effect lessens for the [3,7] case, where the ground state is changed from S_OS to triplet (T) state. Generally, increase of X and/or Y in the peri nitrogen substituted graphenes leads to a decrease in the stability of S_CS with a concurrent decrease in ∆E _LUMO–HOMO. However, peri-bay nitrogen substitution has no tangible effect on altering the ground states of nanoribbons.     

Nano iron oxide with the neural-network morphology

To improve network-functioning, an arc discharge method was developed for the synthesis of nano iron oxide with “neuralnetwork” morphology. Iron wires with diameters of 0.01–0.05 cm were subjected to currents of 50–200 A, until explosions occured in the open air. The XRD and RAMAN spectra of the as-prepared-products indicate formation of nano-Fe₂O₃ (tetragonal and monoclinic) crystals. Their SEM images show fabrication of nano iron oxide with three different morphologies: spheres, chains, and a “neural-network” biological form. While the latter is unprecedented, our fabrications of nano iron oxide with both sphere and chain morphologies are reproductions of previously reported results. The sphere shaped nanoparticles show a uniform distribution with sizes in the range of 50–250 nm. The specifications of the chain nano products appear consistent with those reported.     

P‐Heterocyclic silylenes: a survey of stability with density functional theory

The effects of phosphorous atom on the stability, multiplicity, and reactivity of six‐member cyclic silylenes are investigated at B3LYP/AUG‐cc‐pVTZ//B3LYP/6‐31+G* and MP2/6‐311++G**//B3LYP/6‐31+G* coupled with appropriate isodesmic reactions. From a thermodynamic point of view, 1H‐2‐silaphosphinine‐2‐ylidene ( 1_a ) and 1H‐4‐silaphosphinine‐4‐ylidene ( 2_a ) are relatively the most stable with singlet–triplet energy gaps (ΔE_S–T) of 37.0 and 28.1 kcal/mol, respectively. The calculated energy barrier for the 1,2‐H shift of 1_a to the corresponding 2‐silapyridine ( 1 ) is 26.5 kcal/mol, which is lower than the 28.8 kcal/mol required for the 1,4‐H shift of 2_a to the corresponding 4‐silapyridine ( 2 ). In contrast to the previous reports, isodesmic reactions indicate that π‐donor/σ‐donor phosphorous destabilizes the singlet while stabilizes the triplet state. Both 1_a and 2_a silylenes appear invulnerable to the head‐to‐head as well as the head‐to‐tail dimerization, inviting experimental explorations. Copyright © 2011 John Wiley & Sons, Ltd.     

Umbrella inversions of cyclononatetraenylidenes at ab initio and DFT

Barriers of umbrella inversions for non-planar triplet 2-, 3-, 4-, or 5-X-2,4,6,8-cyclononatetraenylidenes, inverting through planar transition states, appear roughly four times lower in energy than their corresponding singlet states, at ab initio and DFT levels (X = H, F, Cl, Br). Relative activation energies for these racemization (), follow electronegativity for both singlet and/or triplet states of 2-X-2,4,6,8-cyclononatetraenylidenes (F > Cl > Br > H). This trend does not hold for species with halogens further away from the carbenic center: 3-, 4-, or 5-X-2,4,6,8-cyclononatetraenylidenes. Frequency calculations show one negative force constant for all planar species (transition states), while they appear positive for non-planar minima.     

Substituent effects on novel diaminovinylidenes by DFT

Research on Chemical Intermediates - Electronic and steric effects on singlet and triplet symmetric 2,4-diX-vinylidenes with acyclic, cyclic-saturated, and cyclic-unsaturated structures are...