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Liu Yun-Yun, Qiu Fang-Zhou, Zhu Jun, Ren Yi, Lau Kai-Chung
The modified G4(MP2) method was applied to explore microsolvation effects on the reactivity of four solvated normal oxy-nucleophiles YO(-)(CH3OH) n=1,2 (Y = CH3, C2H5, FC2H4, ClC2H4), and five α-oxy-nucleophiles YO(-)(CH3OH) n=1,2 (Y = HO, CH3O, F, Cl, Br), in gas-phase SN2 reactions towards the substrate CH3Cl. Based on a Brønsted-type plot, our calculations reveal that the overall activation barriers of five microsolvated α-oxy-nucleophiles are obviously smaller than the prediction from the correlation line constructed by four normal microsolvated ones to different degrees, and clearly demonstrate the existence of an α-effect in the presence of one or two methanol molecule(s)...
June 2017: Journal of Molecular Modeling
Xiaowen Tang, Ruiming Zhang, Yanwei Li, Qingzhu Zhang, Wenxing Wang
The hydrolysis dechlorination mechanism of a chiral organochlorinepollutant, 1,2-dichloropropane (DCP), catalyzed by haloalkane dehalogenase LinB has been investigated by using a combined quantum mechanics/molecular mechanics method. LinB was confirmed to be enantioselective towards the catabolism of the racemic mixture. Based on the SN2 nucleophilic substitution mechanism, the dechlorination process was identified as the rate-determining step in LinB-catalyzed degradation of 1,2-dichloropropane, the Boltzmann-weighted average potential barrier of which is 18...
May 12, 2017: Bioorganic Chemistry
Dan Han, Baolai Jiang, Ji Feng, Yadong Yin, Wenshou Wang
Visible light-responsive reversible color switching systems are attractive to many applications since visible light has superior penetration and causes far less damages to organic molecules than UV. Here we report that self-doping of Sn2+ in SnO2-x nanocrystals red shifts their absorption to visible region and simultaneously produces oxygen vacancies, which can effectively scavenge photogenerated holes and thus enable color switching of redox dyes using visible light. Wavelength selective switching can also be achieved by coupling the photocatalytic activity of the SnO2-x NCs with the color switching kinetics of different redox dyes...
May 16, 2017: Angewandte Chemie
Balázs Olasz, István Szabó, Gábor Czakó
Bimolecular nucleophilic substitution (SN2) and proton transfer are fundamental processes in chemistry and F(-) + CH3I is an important prototype of these reactions. Here we develop the first full-dimensional ab initio analytical potential energy surface (PES) for the F(-) + CH3I system using a permutationally invariant fit of high-level composite energies obtained with the combination of the explicitly-correlated CCSD(T)-F12b method, the aug-cc-pVTZ basis, core electron correlation effects, and a relativistic effective core potential for iodine...
April 1, 2017: Chemical Science
Shaun G Ard, Nicholas S Shuman, Oscar Martinez, Nicholas R Keyes, Albert A Viggiano, Hua Guo, Jürgen Troe
The pressure and temperature dependences of the reactions of Fe(+) with methyl halides CH3X (X = Cl, Br, I) in He were measured in a selected ion flow tube over the ranges 0.4 to 1.2 Torr and 300-600 K. FeX(+) was observed for all three halides and FeCH3(+) was observed for the CH3I reaction. FeCH3X(+) adducts (for all X) were detected in all reactions. The results were interpreted assuming two-state reactivity with spin-inversions between sextet and quartet potentials. Kinetic modeling allowed for a quantitative representation of the experiments and for extrapolation to conditions outside the experimentally accessible range...
May 19, 2017: Journal of Physical Chemistry. A
Mojgan Heshmat, Timofei Privalov
Using transition-state (TS) calculations, we examined how Lewis acid complexation activates carbonyl compounds in the context of hydrogenation of carbonyl compounds by H2 in Lewis basic (ethereal) solvents containing the Lewis acid of the type (C6F5)3B. We found out that Lewis acid complexation does not activate a ketone sufficiently enough for the direct addition of H2 to O=C unsaturated bond; but, calculations speak quite in favor of the possibly facile heterolytic cleavage of H2 at the activated Lewis acidic carbonyl carbon with the assistance of Lewis basic solvent (1,4-dioxane or THF)...
May 5, 2017: Chemistry: a European Journal
Jana L Markley, Paul R Hanson
The development of a P-tether-mediated, iterative SN2'-cuprate alkylation protocol for the formation of 1,3-skipped polyol stereotetrads is reported. This two-directional synthetic strategy builds molecular complexity from simple, readily prepared C2-symmetric dienediols and unites the chemistry of both temporary phosphite-borane tethers and temporary phosphate tethers-through an oxidative "function switch" of the P-tether itself-to generate intermediates that were previously inaccessible via either method alone...
May 4, 2017: Organic Letters
Maciej Giedyk, Joanna Turkowska, Sandra Lepak, Marcin Marculewicz, Keith Ó Proinsias, Dorota Gryko
Vitamin B12 is a natural cobalt complex that, while reduced to the "supernucleophilic" Co(I) form, can easily react with electrophiles via an SN2 mechanism. It is also shown to react via an SN2' mechanism with allylic compounds allowing for photochemical deprotection of (allyloxy)arenes. A sustainable alternative to commonly used noble metal-catalyzed deprotection reactions is presented.
April 28, 2017: Organic Letters
Peng Peng, Richard R Schmidt
Inverting glycosyltransferases enforce in the active site an intramolecular, acid-base catalyzed glycosidation that, due to proximity of the donor anomeric carbon and the acceptor hydroxyl group, follows an SN2-type reaction. Spacers, tethering donor and acceptor via nonreacting functional groups, led in intramolecular glycosidations to excellent yields and, independent of the donor anomeric configuration, to either the α- or the β-anomer. The requirement of a demanding protecting group pattern confines the application of this efficient method...
April 25, 2017: Accounts of Chemical Research
Jenner Bonanata, Lucía Turell, Laura Antmann, Gerardo Ferrer-Sueta, Santiago Botasini, Eduardo Méndez, Beatriz Alvarez, E Laura Coitiño
Human serum albumin (HSA) has a single reduced cysteine residue, Cys34, whose acidity has been controversial. Three experimental approaches (pH-dependence of reactivity towards hydrogen peroxide, ultraviolet titration and infrared spectroscopy) are used to determine that the pKa value in delipidated HSA is 8.1 ± 0.2 at 37°C and 0.1M ionic strength. Molecular dynamics simulations of HSA in the sub-microsecond timescale show that while sulfur exposure to solvent is limited and fluctuating in the thiol form, it increases in the thiolate, stabilized by a persistent hydrogen-bond (HB) network involving Tyr84 and bridging waters to Asp38 and Gln33 backbone...
April 21, 2017: Free Radical Biology & Medicine
Marcus Brauns, Marvin Mantel, Julie Schmauck, Marian Guder, Martin Breugst, Joerg Pietruszka
Optimized protecting group for allylboronates allows the use of ketones to synthesize all isomers of quaternary homoallylic alcohols with high enantioselectivities. All symmetric isomers of the allylboronate can be prepared in high yields and diastereoselectivities using SN2' reactions. The improved reactivity of the novel protecting group is verified via 1H-NMR kinetics. Mechanistic studies using DFT calculations are conducted to investigate the new findings. Thus, the stereochemical outcome and enhanced reactivity can be rationalized...
April 19, 2017: Chemistry: a European Journal
Doyoung Kim, Min Woo Ha, Suckchang Hong, Cheonhyoung Park, Byungsoo Kim, Jewon Yang, Hyeung-Geun Park
A new efficient synthetic method for chiral α-azido-α-alkylmalonates and α-aryloxy-α-alkylmalonates was developed. The enantioselective α-alkylation of diphenylmethyl tert-butyl α-bromomalonate under phase-transfer catalytic conditions [(S,S)-3,4,5-trifluorophenyl-NAS bromide, 50% KOH, toluene, and -40 °C) provided the corresponding α-bromo-α-alkylmalonates in high chemical yields (≤98%) and high optical yields (≤99% ee). The resulting α-alkylated products were converted to α-azido-α-alkylmalonates (≤96%, ≤97% ee) and α-aryloxy-α-alkylmalonates (≤79%, ≤93% ee) by SN2 substitution with sodium azide and aryloxides, respectively...
May 5, 2017: Journal of Organic Chemistry
Shuai Wang, Madison L McCrea-Hendrick, Cory M Weinstein, Christine A Caputo, Elke Hoppe, James C Fettinger, Marilyn M Olmstead, Philip P Power
The tin(II) hydride [Ar((i)Pr6)Sn(μ-H)]2(Ar((i)Pr6) = C6H3-2,6(C6H2-2,4,6-(i)Pr3)2) (1a) reacts with 2 equiv of ethylene or t-butylethylene at ca. 25 °C to yield Sn2(Ar((i)Pr6))2R2(R = ethyl or t-butylethyl), which exist either as a symmetric distannene Ar((i)Pr6)(R)SnSn(R)Ar((i)Pr6) (2a or 5a) or an unsymmetric stannylstannylene Ar((i)Pr6)SnSnR2Ar((i)Pr6) (3a). In contrast, the less crowded Sn(II) hydride [Ar((i)Pr4)Sn(μ-H)]2 (Ar((i)Pr4) = C6H3-2,6(C6H3-2,6-(i)Pr2)2) (1b) reacts with excess ethylene to give Ar((i)Pr4)(CH2CH3)2Sn(CH2CH2)Sn(CH2CH3)(CHCH2)Ar((i)Pr4) (4) featuring five ethylene equivalents, one of which is dehydrogenated to an vinyl, -CH═CH2, group...
April 28, 2017: Journal of the American Chemical Society
Emanuel Hupf, Marian Olaru, Ciprian I Rat, Christian B Hübschle, Enno Lork, Simon Grabowsky, Stefan Mebs, Jens Beckmann
The nucleophilic substitution reaction of second order (SN2) at a silicon atom is scrutinized using snapshots along a pseudo-reaction coordinate. Phosphine and fluoride represent both attacking and leaving groups in the modeled SN2 reaction. In the experimentally obtained 5-Ph2P-Ace-6-SiMe2F (1) the phosphine moiety and the fluorosilane moiety are forced into immediate proximity through an acenaphthyl scaffold, i.e. they exhibit peri-interactions that serve as the model of the reactant ion-molecule complex and starting point for a theoretical PES scan...
April 10, 2017: Chemistry: a European Journal
Xu Liu, Jing Xie, Jiaxu Zhang, Li Yang, William L Hase
Influences of solvent molecules on SN2 reaction dynamics of microsolvated F(-)(H2O)n with CH3I, for n = 0-3, are uncovered by direct chemical dynamics simulations. The direct substitution mechanism, which is important without microsolvation, is quenched dramatically upon increasing hydration. The water molecules tend to force reactive encounters to proceed through the prereaction collision complex leading to indirect reaction. In contrast to F(-)(H2O), reaction with higher hydrated ions shows a strong propensity for ion desolvation in the entrance channel, diminishing steric hindrance for nucleophilic attack...
April 20, 2017: Journal of Physical Chemistry Letters
Frédéric G Terrade, Jan van Krieken, Bastiaan J V Verkuijl, Elisabeth Bouwman
Despite being a simple dehydration reaction, the industrially relevant conversion of lactic acid to acrylic acid is particularly challenging. For the first time, the catalytic cracking of lactide and poly(lactic acid) to acrylic acid under mild conditions is reported with up to 58 % yield. This transformation is catalyzed by strong acids in the presence of bromide or chloride salts and proceeds through simple SN 2 and elimination reactions.
April 4, 2017: ChemSusChem
Li Yang, Xu Liu, Jiaxu Zhang, Jing Xie
Systematic studies of microsolvation in the gas phase have enriched our knowledge of solvent effects. Here, the dynamics of a prototype SN2 reaction of a hydrated fluoride ion with methyl iodide is uncovered employing direct dynamics simulations that show strikingly distinct features from those determined for an unsolvated system. An indirect scattering is found to prevail, which occurs dominantly by forming hydrated F(-)(H2O)-HCH2I and F(-)(H2O)-CH3I pre-reaction complexes at low energies, but proceeds through their water-free counterparts at higher energies...
April 12, 2017: Physical Chemistry Chemical Physics: PCCP
Debashis Majee, Soumen Biswas, Shaikh M Mobin, Sampak Samanta
A facile, green, metal-free new one-pot synthetic strategy has been developed for easy access to a wide array of medicinally promising functionalized pyridines having an ester, a nitrile or an acetyl group at the C-3 position in good to excellent yields via a domino SN2/elimination/6π-aza-electrocyclization/aromatization reaction of several 4-aryl/hetero-aryl-substituted 5-membered cyclic sulfamidate imines with a broad range of MBH acetates of acrylate/acrylonitrile/MVK in 2-MeTHF promoted by DABCO as an organobase under an O2 atmosphere...
April 11, 2017: Organic & Biomolecular Chemistry
Viktor Tajti, Gábor Czakó
We compute benchmark structures, frequencies, and relative energies for the stationary points of the potential energy surface of the F(-) + CH3CH2Cl reaction using explicitly correlated ab initio levels of theory. CCSD(T)-F12b geometries and harmonic vibrational frequencies are obtained with the aug-cc-pVTZ and aug-cc-pVDZ basis sets, respectively. The benchmark relative energies are determined using a high-level composite method based on CCSD(T)-F12b/aug-cc-pVQZ frozen-core energies, CCSD(T)-F12b/cc-pCVTZ-F12 core electron correlation effects, and CCSD(T)-F12b/aug-cc-pVDZ zero-point energy corrections...
April 3, 2017: Journal of Physical Chemistry. A
Zhen Zhang, Cheng Li, Shao-Hua Wang, Fu-Min Zhang, Xue Han, Yong-Qiang Tu, Xiao-Ming Zhang
A novel and efficient tandem SN2' nucleophilic substitution/oxidative radical cyclization reaction of aryl substituted allylic alcohols with 1,3-dicarbonyl compounds has been developed by using Mn(OAc)3 as an oxidant, which enables the expeditious synthesis of polysubstituted dihydrofuran (DHF) derivatives in moderate to high yields. The use of weakly acidic hexafluoroisopropanol (HFIP) as the solvent rather than AcOH has successfully improved the yields and expanded the substrate scope of this type of radical cyclization reactions...
April 11, 2017: Organic & Biomolecular Chemistry
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