DIPOLAR APROTIC SOLVENT EFFECTS IN THE HYDROLYSIS OF PHENYLMETHANESULFONATES AND PHENYLSULFONYLACETATES

Abstract

The hydrolytic behaviour under alkaline conditions of a group of sulfur compounds containing an active methylene group, in aqueous solvent mixtures with dimethylsulfoxide as the co-solvent has been investigated. The substrates studied are substituted phenyl phenylmethanesulfonates (A), substituted phenyl p-nitrophenylmethanesulfonates (B) and substituted phenylsulfonylacetates (C). It is known that methylenes adjacent to the sulfonyl group are acidic and evidences are available for the formation of the corresponding anions in alkaline solutions. Structure-reactivity correlations strongly suggest that these react not by the conventional addition–elimination mechanism (B_AC ²), but by an elimination-addition mechanism (ElcB) involving a slow decomposition of the corresponding anions. The rate of hydrolysis of (A) increases with increasing percentage of dimethylsulfoxide in the solvent mixtures, whereas, the reverse is the case with (B) and (C). The results are analysed on the basis of a spectrum of pathways in the ElcB mechanism, and on the basis of the relative solvation of ground and transition states of the reaction.     

Flexible and Rigid Amine‐Functionalized Microporous Frameworks Based on Different Secondary Building Units: Supramolecular Isomerism,Selective CO2 Capture,and Catalysis

We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH₂?bdc)(bphz)_0.5]?DMF?H₂O}_n (NH₂?bdc=2‐aminobenzenedicarboxylic acid, bphz=1,2‐bis(4‐pyridylmethylene)hydrazine) composed of a mixed‐ligand system. The first isomer, with a paddle‐wheel‐type Cd₂(COO)₄ secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a μ‐oxo‐bridged Cd₂(μ‐OCO)₂ SBU. Both frameworks are two‐fold interpenetrated and the pore surface is decorated with pendant ?NH₂ and ?N?N? functional groups. Both the frameworks are nonporous to N₂, revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double‐step hysteretic CO₂ adsorption profile, whereas the second isomer shows a typical type I CO₂ profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO₂ among other gases (N₂, O₂, H₂, and Ar), which has been correlated to the specific interaction of CO₂ with the ?NH₂ and ?N?N? functionalized pore surface. DFT calculations for the oxo‐bridged isomer unveiled that the ?NH₂ group is the primary binding site for CO₂. The high heat of CO₂ adsorption (ΔH_ads=37.7 kJ mol^?1) in the oxo‐bridged isomer is realized by NH₂???CO₂/aromatic π???CO₂ and cooperative CO₂???CO₂ interactions. Further, postsynthetic modification of the ?NH₂ group into ?NHCOCH₃ in the second isomer leads to a reduced CO₂ uptake with lower binding energy, which establishes the critical role of the ?NH₂ group for CO₂ capture. The presence of basic ?NH₂ sites in the oxo‐bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.     

Shear viscosity of the ionic liquid 1-n-butyl 3-methylimidazolium hexafluorophosphate [bmim][pf6] computed by reverse nonequilibrium molecular dynamics

Reverse nonequilibrium molecular dynamics and equilibrium molecular dynamics simulations were carried out to compute the shear viscosity of the pure ionic liquid system [bmim][PF 6] at 300 K. The two methods yielded consistent results which were also compared to experiments. The results showed that the reverse nonequilibrium molecular dynamics (RNEMD) methodology can successfully be applied to computation of highly viscous ionic liquids. Moreover, this study provides a validation of the atomistic force-field developed by Bhargava and Balasubramanian ( J. Chem. Phys. 2007, 127, 114510 ) for dynamic properties.     

Equilibrium strategies for multiple interdictors on a common network

In this work, we introduce multi-interdictor games, which model interactions among multiple interdictors with differing objectives operating on a common network. As a starting point, we focus on shortest path multi-interdictor (SPMI) games, where multiple interdictors try to increase the shortest path lengths of their own adversaries attempting to traverse a common network. We first establish results regarding the existence of equilibria for SPMI games under both discrete and continuous interdiction strategies. To compute such an equilibrium, we present a reformulation of the SPMI game, which leads to a generalized Nash equilibrium problem (GNEP) with non-shared constraints. While such a problem is computationally challenging in general, we show that under continuous interdiction actions, an SPMI game can be formulated as a linear complementarity problem and solved by Lemke’s algorithm. In addition, we present decentralized heuristic algorithms based on best response dynamics for games under both continuous and discrete interdiction strategies. Finally, we establish theoretical lower bounds on the worst-case efficiency loss of equilibria in SPMI games, with such loss caused by the lack of coordination among noncooperative interdictors, and use the decentralized algorithms to numerically study the average-case efficiency loss.     

Relative energies of alpha and beta isomers of Keggin dodecatungstogallate

The relative energies of beta Keggin heteropolytungstates, X(n+) W12O40(8-n)-, decrease as X(n+) is varied within period 3, from P5+ to Si4+ to Al3+. With heating of alpha-H5Ga3+ W12O40 at 200 degrees C in water, an equilibrated mixture of alpha (T(d); one 183W NMR signal) and beta (C(3v); three signals; 1:2:1 ratio) isomers is obtained. From deltaG(exp) = -RT ln K(beta-->alpha), in which (from 71Ga NMR spectra) K(beta-->alpha) (= [alpha]/[beta]) = 5.0, beta-GaW12O40(5-) is 0.65 kcal mol(-1) higher in energy than alpha-GaW12O40(5-). This finding is evaluated by analysis of the X-ray crystal structure alpha-K2Na3[GaW12O40] x 9.3 H2O [trigonal, space group P3(2)21, a = 18.9201(13) A, b = 18.9201(13) A, c = 12.5108(12) A, Z = 3, T = 100(2)K], comparison of the Shannon and Prewitt radii and Pauling electronegativities of Al3+ and Ga3+, and insight from density functional theory calculations, which predicted Ebeta - Ealpha = 0.32 kcal mol(-1).     

Crystal Structure Analysis of a New Coumarin Derivative

The title compound (6,6‐dimethyl‐cis‐6H,6aH,7H,12bH,13H‐bis[1]benzopyrano[4,3‐b:4',3'‐d]pyran‐13‐one) crystallizes in monoclinic space group P2₁ /c with Z = 4. The unit cell dimensions are a = 8.6231(2) Å, b =10.0260(2) Å, c = 19.8376(2) Å, and β = 102.1(1)°, V = 1674.51(5) ų , D_cal = 1.326 Mg/m³. The coumarin moiety is in the planar conformation, the dioxadecalin moiety is cis fused and within the dioxadecalin moiety both the rings are in half cahir/sofa conformations. The structure has many C‐H … O type interactions.