01724nas a2200157 4500008004100000022001400041245007900055210006900134260007100203300001400274490000800288520112200296100001701418700001601435856011501451 2013 eng d a1089-563900aWhy does water accelerate organic reactions under heterogeneous condition?0 aWhy does water accelerate organic reactions under heterogeneous  a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcMAR a2446-24540 v1173 a

An exhaustive kinetic analysis has been carried out to offer the convincing evidence of the involvement of the oil water interface in guiding ``on water organic reaction'' mechanism. We have tuned the interface to prove its indispensable efficacy to make on water reaction a unique type among water mediated organic reactions. Sensitive techniques have established the preferential salvation of polarizable ions at the water surface. The experimental methods have been developed to control the molecular structure of oil water interface in situ. Temperature-dependent analyses have also been presented to understand the enthalpic and entropic modifications of the interfacial water molecules during a heterogeneous reaction. Both of our kinetic and thermodynamic outcomes have univocally established that the hydrogen-bonding ability of the surface water molecules plays a critical role in deciding the on water organic reaction mechanism. The results have important implications on understanding the role of small water molecules adjacent to the reactants during the reactions discussed in this investigation.

1 aManna, Arpan1 aKumar, Anil uhttps://library.ncl.res.in/content/why-does-water-accelerate-organic-reactions-under-heterogeneous-condition-002379nas a2200181 4500008004100000022001400041245013900055210006900194260007100263300001400334490000800348520164000356100001701996700002102013700001602034700001702050856013002067 2014 eng d a1520-610600aAtypical energetic and kinetic course of excited-state intramolecular proton transfer (ESIPT) in room-temperature protic ionic liquids0 aAtypical energetic and kinetic course of excitedstate intramolec a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcMAR a2487-24980 v1183 a

The excited-state intramolecular proton-transfer (ESIPT) process in 1,8-dihydroxyanthraquinone (18DHAQ) dye has been investigated in protic ionic liquid (PIL) solvents using photochemical measurements. The results demonstrate noteworthy modulations in both steady-state and time-resolved emission characteristics of excited normal (N*) and tautomeric (T*) forms of the dye. That the emission of T* increases unexpectedly upon increasing solvent viscosity indicates that subsequent to the initial forward ESIPT, there is also a relatively slower back ESIPT process involved for the excited dye. It is inferred that the propensity of this back ESIPT process is determined by the dynamics of the diffusive solvent relaxation, a process that is known to be strongly viscosity-dependent in ionic liquids. Evidence of both forward and back ESIPT for the dye has been obtained from femtosecond fluorescence up-conversion measurements. While an unusually fast forward ESIPT is clearly observed in all of the PILs studied, the uncommon back ESIPT process is distinctly indicated in PIL solvents having lower viscosities, certainly due to reasonably fast diffusive solvent relaxation in these solvents that causes a temporal modulation in the energies of the normal and tautomeric forms within a reasonably short time and thereby brings down the energy of N* compared to that of T*, triggering the back ESIPT process. Observation of solvent-viscosity-dependent back ESIPT is an intriguing finding for the present study as to the best of our knowledge, such a behavior has so far not been reported in the literature for the ESIPT reaction.

1 aManna, Arpan1 aSayed, Mhejabeen1 aKumar, Anil1 aPal, Haridas uhttps://library.ncl.res.in/content/atypical-energetic-and-kinetic-course-excited-state-intramolecular-proton-transfer-esipt-001584nas a2200157 4500008004100000022001400041245011200055210006900167260007700236300001400313490000700327520093000334100001701264700001601281856012901297 2014 eng d a1439-423500aInvoking pairwise interactions in water-promoted diels-alder reactions by using ionic liquids as cosolvents0 aInvoking pairwise interactions in waterpromoted dielsalder react aBOSCHSTRASSE 12, D-69469 WEINHEIM, GERMANYbWILEY-V C H VERLAG GMBHcOCT a3067-30770 v153 a

Rate constants and derived activation parameters of organic reactions in aqueous media, in particular Diels-Alder reactions, are sensitive to the presence of cosolvents in water. To enhance the solubility window of water, we introduced ionic liquids as cosolvents in the aqueous Diels-Alder reaction between anthracene-9-carbinol and N-ethylmaleimide. The reactive potentials of the organic compounds are parameterized by using semi-empirical quantum chemical methods. The principle of Savage-Wood additivity of group interactions is used to quantify the pairwise group interactions among chemically inert ionic liquids and organic reactants, both at initial and transition states of the reaction. The present approach shows promise, as the use of simple calculations from easily available kinetic data can help researchers to understand the versatility of green ionic-liquid alternatives to volatile organic solvents.

1 aManna, Arpan1 aKumar, Anil uhttps://library.ncl.res.in/content/invoking-pairwise-interactions-water-promoted-diels-alder-reactions-using-ionic-liquids-003636nas a2200193 4500008004100000022001400041245012000055210006900175260007100244300001600315490000800331520288200339100002103221700001703242700002103259700001603280700001703296856012903313 2014 eng d a1520-610600aObservation of the marcus inverted region for bimolecular photoinduced electron-transfer reactions in viscous media0 aObservation of the marcus inverted region for bimolecular photoi a1155 16TH ST, NW, WASHINGTON, DC 20036 USAbAMER CHEMICAL SOCcSEP a10704-107150 v1183 a

The general observation of Marcus inverted region (MIR) for bimolecular electron-transfer (ET) reactions in different viscous media, e.g., micelles, reverse micelles, vesicles, ionic liquids, DNA scaffold, etc. has been doubted in some recent publications arguing limitations in SternVolmer (SV) analysis to account for the static and transient stages of quenching in these slow diffusing media. Thus, following a theoretical treatment based on a spherically symmetric diffusion equation coupled with conventional Marcus ET description, it has been suggested that the MIR observed in viscous media arises due to the inadequate consideration of different quenching regimes and also due to the differential excited-state lifetimes of the fluorophores used than a genuine one (J. Am. Chem. Soc. 2012, 134, 11396). However, the overall treatment in this study is severely compromised by setting the minimum solvent reorganization energy (?s) to (lambda) to similar to 0.96 eV while fitting the experimental data, which unambiguously suggests that the inversion in ET rate will never appear in the exergonicity (-Delta G(0)) range of 0.16 to 0.71 eV, as is the case for the studied ET systems. Besides, the applicability of the conventional Marcus ET model (instead of Sumi-Marcus two-dimensional ET model) in such extremely viscous media with exceptionally slow solvent response is highly debatable and perhaps is the main cause of the failure in fitting the experimental data quite satisfactorily. In the present study involving ultrafast ET quenching for coumarin derivatives by dimethylaniline donor in viscous ionic liquid media, we demonstrate clear MIR for the intrinsic ET rates, directly obtained from the ultrafast decay components of 110 ps, a time scale in which diffusion of reactants is negligible and the ET rates are either faster than or, at the most, competitive with the solvent reorganization. The appearance of MIR at ?Delta G(0) similar to-0.5 eV, significantly lower than expected from the lambda(s) value, further substantiate the nonapplicability of conventional ET description but certainly advocate for the applicability of the SumiMarcus two-dimensional ET model in such media. Moreover, no obvious correlation has experimentally been observed between the excited-state lifetimes of the coumarin derivatives and the ET rates for a large number of dyes used in the present study. On the basis of the present results and drawing inferences from reported literatures in viscous media, we conclude that not only is the appearance of MIR very genuine but also the mechanistic model necessary to account the observed facts for the bimolecular ET reactions in a viscous medium is the two-dimensional ET description, which deals with an extremely slow relaxing solvent coordinate and a fast relaxing intramolecular coordinate to describe the ET reactions.

1 aKumbhakar, Manoj1 aManna, Arpan1 aSayed, Mhejabeen1 aKumar, Anil1 aPal, Haridas uhttps://library.ncl.res.in/content/observation-marcus-inverted-region-bimolecular-photoinduced-electron-transfer-reactions-001454nas a2200265 4500008004100000022001400041245006900055210006700124260006700191300001200258490000700270520059600277653002300873653002500896653000900921653001800930653001500948653002900963653001400992100002101006700001701027700002501044700001601069856010301085 2015 eng d a0894-323000aWater-promoted diels-alder reaction in quaternary ammonium salts0 aWaterpromoted dielsalder reaction in quaternary ammonium salts a111 RIVER ST, HOBOKEN 07030-5774, NJ USAbWILEY-BLACKWELLcNOV a665-6730 v283 a

{Prevailing classification of salts based on their effect in solubility and stability of proteins in aqueous solution predicts that tetraalkylammonium salts, guanidinium chloride (GnCl), LiClO4 act as salting-in (S/I) and LiCl, NaCl act as salting-out (S/O) in aqueous conditions. In the same context the behaviour of GnCl, LiClO4 and LiCl are contradictory in polar solvents like ethylene glycol and formamide. In these solvents, expected salt effect shows just opposite nature from their usual expectation. However, in the aqueous solution salts like tetraalkylammonium halide (R4NX

10aDelta G(solvation)10aDiels-Alder reaction10ak(s)10akinetic study10asolubility10atetraalkylammonium salts10aviscosity1 aNagare, Amit, S.1 aManna, Arpan1 aSonawane, Pramod, D.1 aKumar, Anil uhttps://library.ncl.res.in/content/water-promoted-diels-alder-reaction-quaternary-ammonium-salts-001555nas a2200157 4500008004100000245009100041210006900132260000800201300001400209490000700223520099800230100002101228700001701249700001601266856011501282 2016 eng d00aCan a diels-alder reaction accelerate in a supersaturated solvent at room temperature?0 aCan a dielsalder reaction accelerate in a supersaturated solvent cAUG a8355-83630 v403 a

A new supersaturated solvent is proposed to accelerate the Diels–Alder reaction between cyclopentadiene and methyl acrylate by several times. The proposed supersaturated solvent consists of various carbohydrates, organic acid and organic ketone in water, beyond their solubility limits in water, at room temperature. The results demonstrate that the presence of excess –OH groups from the carbohydrates plays a pivotal role leading to the increased reactivity and selectivity of the Diels–Alder reaction. The role of hydrogen bond accelerators and polarity of the solvent have been analyzed through a comparative study of the same reaction in similar green solvents. Collision-controlled reaction theory has been invoked to understand the role of encounter complexes to accelerate such a reaction at the molecular level in such highly viscous supersaturated solvent. No detrimental effects from the high viscosity of the new solvent medium on the reaction kinetics was been noted.

1 aNagare, Amit, S.1 aManna, Arpan1 aKumar, Anil uhttps://library.ncl.res.in/content/can-diels-alder-reaction-accelerate-supersaturated-solvent-room-temperature01274nas a2200229 4500008004100000022001400041245010000055210006900155260007500224300001400299490000700313520045900320653002500779653001500804653001800819653001300837653002200850100001900872700001700891700001600908856012000924 2016 eng d a1439-423500aSpectacular rate enhancement of the diels-alder reaction at the ionic liquid/n-hexane interface0 aSpectacular rate enhancement of the dielsalder reaction at the i aPOSTFACH 101161, 69451 WEINHEIM, GERMANYbWILEY-V C H VERLAG GMBHcJUL a1969-19720 v173 a

The use of the ionic liquid/n-hexane interface as a new class of reaction medium for the Diels-Alder reaction gives large rate enhancements of the order of 10(6) to 10(8) times and high stereoselectivity, as compared to homogeneous media. The rate enhancement is attributed to the H-bonding abilities and polarities of the ionic liquids, whereas the hydrophobicity of ionic liquids was considered to be the factor in controlling stereoselectivity.

10aDiels-Alder reaction10aInterfaces10aionic liquids10akinetics10astereoselectivity1 aBeniwal, Vijay1 aManna, Arpan1 aKumar, Anil uhttps://library.ncl.res.in/content/spectacular-rate-enhancement-diels-alder-reaction-ionic-liquidn-hexane-interface