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1.
Temperature dependences of the relative reactivity of substituted phenols RC6H4OH in the presence of potassium hydrogen carbonate and of potassium phenoxides RC6H4O−K+ toward 2,4-dinitrophenyl benzoate in dimethylformamide were studied using the competitive reactions technique. Correlation
analysis of the relative rate constants k
R/k
H and differences in the activation parameters (ΔΔH
≠ and ΔΔS
≠) of competitive reactions revealed the existence of two isokinetic series for each type of nucleophiles. The mechanism of
transesterification was interpreted in terms of an approach based on analysis of the effect of substituent in the nucleophile
on the activation parameters. 相似文献
2.
Dr. Tiziana Marino Prof. Nino Russo Prof. Marirosa Toscano 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(6):2185-2192
To elucidate the working mechanism of the “broad substrate specificity” by the Pseudomonas aeruginosa aryl sulfatase (PAS) enzyme, we present here a full quantum chemical study performed at the density functional level. This enzyme is able to catalyze the hydrolysis of the original p‐nitrophenyl‐sulfate (PNPS) substrate and the promiscuous p‐nitrophenyl‐phosphate (PNPP) one with comparable reaction kinetics. Based on the obtained results, a multistep mechanism including activation of the nucleophile, the nucleophilic attack, and the cleavage of the S? O (P? O) bond is proposed. Regarding the phosphate monoester, the results indicate that only some steps of the promiscuous reaction are identical to those in the native process. Differences concern mainly the last step in which the His115 residue acts as a general base to accept the proton by the O atom of the FGly51 in the PNPS, whereas in PNPP, the Asp317 protonated residue works as a general acid to deliver a proton by a water molecule to the oxygen atom of the C? O bond. The shapes of the relative potential‐ energy surface (PES) are similar in the two examined cases but the rate‐determining step is different (nucleophile attack vs. nucleophile activation). The influence of the dispersion contributions on the investigated reactions was also taken into account. 相似文献
3.
Kaliyaperumal Thanigaimani Annamalai Subashini Packianathan Thomas Muthiah Daniel E. Lynch Ray J. Butcher 《Acta Crystallographica. Section C, Structural Chemistry》2009,65(2):o42-o45
In the crystal structures of 2‐amino‐4,6‐dimethoxypyrimidinium 2,4,6‐trinitrophenolate (picrate), C6H10N3O2+·C6H2N3O7−, (I), and 2,4‐diamino‐5‐(4‐chlorophenyl)‐6‐ethylpyrimidin‐1‐ium (pyrimethaminium or PMN) picrate dimethyl sulfoxide solvate, C12H14ClN4+·C6H2N3O7−·C2H6OS, (II), the 2‐amino‐4,6‐dimethoxypyrimidine and PMN cations are protonated at one of the pyrimidine N atoms. The picrate anion interacts with the protonated cations through bifurcated N—H...O hydrogen bonds, forming R21(6) and R12(6) ring motifs. In (I), Z′ = 2. In (II), two inversion‐related PMN cations are connected through a pair of N—H...N hydrogen bonds involving the 4‐amino group and the uncharged N atom of the pyrimidine ring, forming a cyclic hydrogen‐bonded R22(8) motif. In addition to the pairing, the O atom of the dimethyl sulfoxide solvent molecule bridges the 2‐amino and 4‐amino groups on both sides of the paired bases, resulting in a self‐complementary …DADA… array of quadruple hydrogen‐bonding patterns. 相似文献
4.
Violetta Patroniak Wanda Radecka‐Paryzek Maciej Kubicki 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(9):o511-o513
The structure of a trifluoromethanesulfonate salt of a nontypical triply protonated linear tetramine, C7H23N43+·3CF3SO3−, with a layered crystal structure is presented. One N atom remains unprotonated. The conformation of the cation is enforced by intra‐ and intermolecular hydrogen bonds. The crystal structure is built of ca 10 Å deep layers, within which cations and anions are hydrogen bonded. Each layer is only weakly bound to its neighbours. This study shows a rare example of an unsymmetrically protonated polyamine and the relation between the lack of protonation, intramolecular hydrogen bonding and the conformation of the cation. 相似文献
5.
Probing the reactivity of microhydrated α‐nucleophile in the anionic gas‐phase SN2 reaction
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Wen‐Yang Zhao Jie Yu Si‐Jia Ren Xi‐Guang Wei Fang‐Zhou Qiu Peng‐Hui Li He Li Yi‐Peng Zhou Chang‐Zhen Yin An‐Pu Chen Hao Li Lei Zhang Jun Zhu Yi Ren Kai‐Chung Lau 《Journal of computational chemistry》2015,36(11):844-852
To probe the kinetic performance of microsolvated α‐nucleophile, the G2(+)M calculations were carried out for the gas‐phase SN2 reactions of monohydrated and dihydrated α‐oxy‐nucleophiles XO?(H2O)n = 1,2 (X = HO, CH3O, F, Cl, Br), and α‐sulfur‐nucleophile, HSS?(H2O)n = 1,2, toward CH3Cl. We compared the reactivities of hydrated α‐nucleophiles to those of hydrated normal nucleophiles. Our calculations show that the α‐effect of monohydrated and dihydrated α‐oxy‐nucleophiles will become weaker than those of unhydrated ones if we apply a plot of activation barrier as a function of anion basicity. Whereas the enhanced reactivity of monohydrated and dihydrated ROO? (R = H, Me) could be observed if compared them with the specific normal nucleophiles, RO? (R = H, Me). This phenomena can not be seen in the comparisons of XO?(H2O)n = 1,2 (X = F, Cl, Br) with ClC2H4O?(H2O)n = 1,2, a normal nucleophile with similar gas basicity to XO?(H2O)n = 1,2. These results have been carefully analyzed by natural bond orbital theory and activation strain model. Meanwhile, the relationships between activation barriers with reaction energies and the ionization energies of α‐nucleophile are also discussed. © 2015 Wiley Periodicals, Inc. 相似文献
6.
Kasthuri Balasubramani Packianathan Thomas Muthiah Urszula Rychlewska Agnieszka Plutecka 《Acta Crystallographica. Section C, Structural Chemistry》2005,61(10):o586-o588
The title compound, 2,4‐diamino‐5‐(4‐chlorophenyl)‐6‐ethylpyrimidine‐1,3‐diium dinitrate, C12H15ClN42+·2NO3−, contains two crystallographically independent pyrimethamine (PMN) molecules, which differ in the relative orientations of the pyrimidine and benzene rings and of the ethyl substitutents. In both pyrimethamine molecules, all the pyrimidine N atoms are protonated, unlike most related compounds, in which only one pyrimidine N atom is protonated. The two pyrimethamine moieties are bridged by a variety of N—H⋯O(nitrate) interactions, including some three‐centre hydrogen bonds. 相似文献
7.
Balasubramanian Sridhar Krishnan Ravikumar 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(5):o265-o267
Ropinirole hydrochloride, or diethyl[2‐(2‐oxo‐2,3‐dihydro‐1H‐indol‐4‐yl)ethyl]ammonium chloride, C16H25N2O+·Cl−, belongs to a class of new non‐ergoline dopamine agonists which bind specifically to D2‐like receptors with a selectivity similar to that of dopamine (D3 > D2 > D4). The N atom in the ethylamine side chain is protonated and there is a hydrogen bond between it and the Cl− ion. In the crystal structure, two cations and two anions form inversion‐related cyclic dimers via N—H⋯Cl hydrogen bonds. 相似文献
8.
Montserrat Alfonso Yi Wang Helen Stoeckli-Evans 《Acta Crystallographica. Section C, Structural Chemistry》2001,57(10):1184-1188
5,6-Bis(2-pyridyl)pyrazine-2,3-dicarboxylic acid exists as an inner-salt zwitterion, 3-carboxy-5-(2-pyridinio)-6-(2-pyridyl)pyrazine-2-carboxylate, (Ia), C16H10N4O4. The adjacent pyridine and pyridinium rings are almost coplanar due to the presence of an intramolecular hydrogen bond involving the pyridine N atom and the NH H atom of the pyridinium group. In the crystal of (Ia), symmetry-related molecules are hydrogen bonded via the carboxylic acid OH group and one of the carboxylate O atoms to form a polymer, which exhibits a channel-type structure. In the HCl, HClO4 and HPF6 salts, 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium chloride 2.25-hydrate, (II), C16H11N4O4+·Cl−·2.25H2O, 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium perchlorate trihydrate, (IIIa), C16H11N4O4+·ClO4−·3H2O, and 6-carboxy-5-carboxylatopyrazine-2,3-diyldi-2-pyridinium hexafluorophosphate trihydrate, (IIIb), C16H11N4O4+·PF6−·3H2O, both pyridine rings are protonated. In the perchlorate form, and in the isomorphous hexafluorophosphate form, the molecule possesses C2 symmetry, with has a symmetrical intramolecular hydrogen bond involving the adjacent carboxylate and carboxylic acid substituents. In the crystals of the chloride and perchlorate (or hexafluorophosphate) salts, hydrogen-bonded polymers are formed which are three-dimensional and one-dimensional, respectively. 相似文献
9.
Yong Wang Dong‐Xia Zhu Zhong‐Min Su Kui‐Zhan Shao Ya‐Hui Zhao 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(1):m70-m72
The novel title ZnII coordination polymer, poly[bis(μ‐6‐thioxo‐1,6‐dihydropyridine‐3‐carboxylato‐κ2S:O)zinc(II)], [Zn(C6H4NO2S)2]n, consists of two crystallographically independent zinc centers and two 6‐mercaptonicotinate (Hmna−) ligands. Each ZnII atom is four‐coordinated and lies at the center of a distorted tetrahedral ZnS2O2 coordination polyhedron, bridged by four Hmna− ligands to form a two‐dimensional (4,4)‐network. Each Hmna− ion acts as a bridging bidentate ligand, coordinating to two ZnII atoms through the S atom and a carboxyl O atom. The metal centers reside on twofold rotation axes. The coordination mode of the S atoms and N—H...O hydrogen‐bonding interactions between the protonated N atoms and the uncoordinated carboxyl O atoms give the extended structure a wavelike form. 相似文献
10.
Yu Lu Ruihua Zhao Jiandong Guo Zheyuan Liu Wasihun Menberu Prof. Zhi-Xiang Wang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(15):3939-3949
Acceptorless dehydrogenative coupling (ADC) reactions generally involve a nucleophile (e.g., amine) as a coupling partner. Intriguingly, it has been reported that nitriles could also act as nucleophiles in ADC reactions, achieving the α-olefination of nitriles with primary or secondary alcohols by employing a manganese or ruthenium pincer complex as the catalyst, respectively. Although different mechanisms have been postulated for the two catalytic systems, the results of our DFT mechanistic study, reported herein, have allowed us to propose a unified mechanism to account for both nitrile α-olefinations. The reactions take place in four stages, namely alcohol dehydrogenation, nitrile activation to generate a nucleophilic metal species, coupling of an aldehyde or ketone with the metal species to form a C−C bond and to transfer a nitrile (Cα−)H atom to the carbonyl group, and dehydration by transferring the protonic (N−)H to the hydroxy group. A notable feature of the coupling stage is the activation of water or alcohol to give an intermediate featuring an OH−- or OR−-like group that activates a nitrile Cα−H bond. Moreover, the mechanism can even be applied to the base (KOtBu, modeled by the (KOtBu)4 cluster)-catalyzed Knoevenagel condensation of nitriles with ketones, which further indicates the generality of the mechanism and the resemblance of the metal pincer complexes to the (KOtBu)4 base. We expect these in-depth mechanistic insights and the finding of the resemblance of the metal pincer complexes to the (KOtBu)4 cluster could assist the development of new ADC reactions. 相似文献
11.
Lusbely M. Belandria Asilo J. Mora Gerzon E. Delgado Alexander Briceo 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(2):o88-o91
The title salt, C6H12NO2+·C6H7O4− or ISO+·CBDC−, is an ionic ensemble assisted by hydrogen bonds. The amino acid moiety (ISO or piperidine‐4‐carboxylic acid) has a protonated ring N atom (ISO+ or 4‐carboxypiperidinium), while the semi‐protonated acid (CBDC− or 1‐carboxycyclobutane‐1‐carboxylate) has the negative charge residing on one carboxylate group, leaving the other as a neutral –COOH group. The –+NH2– state of protonation allows the formation of a two‐dimensional crystal packing consisting of zigzag layers stacked along a separated by van der Waals distances. The layers extend in the bc plane connected by a complex network of N—H...O and O—H...O hydrogen bonds. Wave‐like ribbons, constructed from ISO+ and CBDC− units and described by the graph‐set symbols C33(10) and R33(14), run alternately in opposite directions along c. Intercalated between the ribbons are ISO+ cations linked by hydrogen bonds, forming rings described by the graph‐set symbols R66(30) and R42(18). A detailed analysis of the structures of the individual components and the intricate hydrogen‐bond network of the crystal structure is given. 相似文献
12.
Ondej Kaman
ubomír Smr
ok Rbert Gyepes David Havlí
ek 《Acta Crystallographica. Section C, Structural Chemistry》2012,68(2):o57-o60
The triclinic structure of the title compound, C6H8N+·H2PO4−, with three symmetry‐independent structural units (Z′ = 3), is formed of separate organic and inorganic layers alternating along the b axis. The building blocks of the inorganic layer are deformed H2PO4 tetrahedra assembled into infinite ladders by short and hence strong hydrogen bonds. The anilinium cations forming the organic layer are not hydrogen bonded to one another, but they are anchored by four N—H...O crosslinks between the dihydrogen phosphate chains of adjacent ladders. Two H atoms of each –NH3 group then form one normal and one bifurcated N—H...O hydrogen bond to the P=O oxygens of two tetrahedra of one chain, while the third H atom is hydrogen bonded to the nearest O atom of an adjacent chain belonging to another dihydrogen phosphate ladder. 相似文献
13.
M.F. Semmelhack G.R. Clark J.L. Garcia J.J. Harrison Y. Thebtaranonth W. Wulff A. Yamashita 《Tetrahedron》1981,37(23):3957-3965
The electrophilic reactivity of arenes coordinated to the chromium tricarbonyl unit has been developed into several distinct methods for coupling carbon nucleophiles with aromatic rings. Addition of the nucleophile produces stable η5-cyclohexadienyl chromium complexes which can be oxidized to induce loss of the endo hydrogen and the metal, overall nucleophilic substitution for hydrogen. Alternatively, the intermediate can be protonated and the resulting cyclohexa-1,3-diene can be detached from the chromium, effecting nucleophilic addition with reduction of one double bond. If a halogen (F, Cl) is present as a ring substituent, and if the nucleophile can migrate about the arene ligand, then loss of halide can occur parallel with classical nucleophilic aromatic substitution for halogen in electron-deficient haloarenes.With substituted arenes, the regioselectivity of addition becomes important and is often very high. Particularly useful are strong resonance donor substituents (RO-, R2N-, F-) where selectivity for meta attack is high. Indole provides an excellent example of selective activation, as the six-membered ring complexes selectively and is then susceptible to nucleophilic substitution, predominantly at the 4 and 7 positions.Substitution for halogen is a somewhat limited process and depends upon the nature of the nucleophile. Very reactive nucleophiles add to unsubstituted positions and are often slow to isomerize to the ipso position from which loss of halide can occur. 相似文献
14.
Genivaldo Júlio Perptuo Jan Janczak 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(5):o271-o273
Crystals of the title compound, C4H8N5+·C2F3O2−, are built up of singly protonated 2,4‐diamino‐6‐methyl‐1,3,5‐triazin‐1‐ium cations and trifluoroacetate anions. The CF3 group of the anion is disordered. The oppositely charged ions interact via almost linear N—H...O hydrogen bonds, forming a CF3COO−...C4H8N5+ unit. Two units related by an inversion centre interact through a pair of N—H...N hydrogen bonds, forming planar (CF3COO−...C4H8N5+...C4H8N5+·CF3COO−) aggregates that are linked by a pair of N—H...O hydrogen bonds into chains running along the c axis. 相似文献
15.
A. A. Zaitsev I. A. Vatsadze I. L. Dalinger V. V. Kachala Yu. V. Nelyubina S. A. Shevelev 《Russian Chemical Bulletin》2009,58(10):2109-2117
The method for preparation of 1-(2,4-dinitrophenyl)-4-methyl-3,5-dinitropyrazole has been developed. Due to the larger CH-acidity
of 4-Me-group compared to 1,4-dimethyl-3,5-dinitropyrazole, 1-(2,4-dinitrophenyl)-4-methyl-3,5-dinitropyrazole is capable
of reacting with substituted benzaldehydes to afford 4-[(E)-2-arylvinyl]-1-(2,4-dinitrophenyl)-3,5-dinitropyrazoles. Under the action of nucleophiles, dinitrophenyl group is detached
from the former compounds leading to previously unknown N-unsubstituted 4-[(E)-2-arylvinyl]-3,5-dinitropyrazoles. 相似文献
16.
Jan Janczak Genivaldo Julio Perptuo 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(6):o349-o352
The crystal structure of the title melaminium salt, bis(2,4,6‐triamino‐1,3,5‐triazin‐1‐ium) dl ‐malate tetrahydrate, 2C3H7N6+·C4H4O52−·4H2O, consists of singly protonated melaminium residues, dl ‐malate dianions and water molecules. The melaminium residues are connected into chains by four N—H⃛N hydrogen bonds, and these chains form a stacking structure along the c axis. The dl ‐malate dianions form hydrogen‐bonded chains and, together with hydrogen‐bonded water molecules, form a layer parallel to the (100) plane. The conformation of the malate ion is compared with an ab initio molecular‐orbital calculation. The oppositely charged moieties, i.e. the stacks of melaminium chains and hydrogen‐bonded dl ‐malate anions and water molecules, form a three‐dimensional polymeric structure, in which N—H⃛O hydrogen bonds stabilize the stacking. 相似文献
17.
Yu‐Hong Xue Duan‐Jun Xu Jian‐Ming Gu 《Acta Crystallographica. Section C, Structural Chemistry》2003,59(10):m387-m389
The crystal structure of the title compound, [Co(C4H2O4)(C7H6N2)3]n, consists of polymeric chains of the CoII complex. Two maleate dianions and three benzimidazole ligands coordinate to the CoII atom with a distorted octahedral geometry. The maleate dianions bridge neighbouring CoII atoms via both terminal carboxylic acid groups, one of which is monodentate and the other bidentate, to form a helical structure of alternating maleate dianions and CoII atoms, with a pitch height of 9.2667 (17) Å. The absolute structure has been determined, and the crystal contains only right‐handed helices. Intrahelical N—H⋯O hydrogen bonds stabilize the helical structure, while interhelical N—H⋯O hydrogen bonds link neighbouring helices to form the supramolecular structure. 相似文献
18.
Vinogradov V. M. Dalinger I. L. Starosotnikov A. M. Shevelev S. A. 《Russian Chemical Bulletin》2001,50(3):464-469
A new procedure was developed for the preparation of 4,6-dinitro-3-R-benzo[d]isoxazoles (R are derivatives of the aldehyde group) based on 2,4,6-trinitrophenylacetaldehyde. The resulting compounds are characterized by the regiospecific substitution of the nitro group at position 4 under the action of anionic nucleophiles RS–, RO–, F–, or N3
–, which allowed the development of a new method for the preparation of previously unknown 4-Nu-6-nitro-3-R-benzo[d]isoxazoles (Nu is the residue of a nucleophile). At the same time, oxidative nucleophilic substitution under the action of anions of some -dicarbonyl compounds leads to the replacement of the hydrogen atom at position 7 with the corresponding C-nucleophiles. 相似文献
19.
20.
Tom Bettens Dr. Mercedes Alonso Prof. Dr. Frank De Proft Dr. Trevor A. Hamlin Prof. Dr. F. Matthias Bickelhaupt 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(17):3884-3893
The ability to understand and predict ambident reactivity is key to the rational design of organic syntheses. An approach to understand trends in ambident reactivity is the hard and soft acids and bases (HSAB) principle. The recent controversy over the general validity of this principle prompted us to investigate the competing gas-phase SN2 reaction channels of archetypal ambident nucleophiles CN−, OCN−, and SCN− with CH3Cl (SN2@C) and SiH3Cl (SN2@Si), using DFT calculations. Our combined analyses highlight the inability of the HSAB principle to correctly predict the reactivity trends of these simple, model reactions. Instead, we have successfully traced reactivity trends to the canonical orbital-interaction mechanism and the resulting nucleophile–substrate interaction energy. The HOMO–LUMO orbital interactions set the trend in both SN2@C and SN2@Si reactions. We provide simple rules for predicting the ambident reactivity of nucleophiles based on our Kohn–Sham molecular orbital analysis. 相似文献