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Gallegos M, Costales A, Martín Pendás Á. Does Steric Hindrance Actually Govern the Competition between Bimolecular Substitution and Elimination Reactions? J Phys Chem A 2022; 126:1871-1880. [PMID: 35290051 PMCID: PMC8958592 DOI: 10.1021/acs.jpca.2c00415] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Bimolecular nucleophilic substitution (SN2) and elimination (E2) reactions are prototypical examples of competing reaction mechanisms, with fundamental implications in modern chemical synthesis. Steric hindrance (SH) is often considered to be one of the dominant factors determining the most favorable reaction out of the SN2 and E2 pathways. However, the picture provided by classical chemical intuition is inevitably grounded on poorly defined bases. In this work, we try to shed light on the aforementioned problem through the analysis and comparison of the evolution of the steric energy (EST), settled within the IQA scheme and experienced along both reaction mechanisms. For such a purpose, the substitution and elimination reactions of a collection of alkyl bromides (R-Br) with the hydroxide anion (OH-) were studied in the gas phase at the M06-2X/aug-cc-pVDZ level of theory. The results show that, generally, EST recovers the appealing trends already anticipated by chemical intuition and organic chemistry, supporting the role that SH is classically claimed to play in the competition between SN2 and E2 reactions.
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Affiliation(s)
- Miguel Gallegos
- Department of Analytical and Physical Chemistry, University of Oviedo, E-33006 Oviedo, Spain
| | - Aurora Costales
- Department of Analytical and Physical Chemistry, University of Oviedo, E-33006 Oviedo, Spain
| | - Ángel Martín Pendás
- Department of Analytical and Physical Chemistry, University of Oviedo, E-33006 Oviedo, Spain
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2
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Ieritano C, Hopkins WS. "Thermometer" Ions Can Fragment Through an Unexpected Intramolecular Elimination: These Are Not the Fragments You Are Looking For. J Phys Chem Lett 2021; 12:5994-5999. [PMID: 34161734 DOI: 10.1021/acs.jpclett.1c01538] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Benzylpyridinium analogs are effective thermometer ions since monitoring the formation of the benzylium fragment produced from heterolytic cleavage of the C-N bond can be linked to the ion's internal energy. In this study, three para-substituted benzylpyridinium ions containing ethoxy (OEt), isopropoxy (OiPr) and tert-butoxy (OtBu) substitutents were synthesized and evaluated as chemical thermometers. Intriguingly, the product ion spectra of the three benzylpyridinium ions were dominated by m/z 107 instead of the anticipated benzylium species. Deuterium labeling suggested that the m/z 107 fragment resulted from an intramolecular elimination (Ei), which formed via a four-membered transition state (TS). The fragmentation pathway appears to be an anomaly within the mass spectrometry literature, as four-membered pericyclic TSs are usually accompanied by the formation of an exceptionally stable neutral molecule (e.g., CO2). Quantum-chemical calculations confirmed our hypothesis that stabilization of the strained TS is afforded by hyperconjugation (ΔG‡ tert-butoxy < isopropyoxy < ethoxy).
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Affiliation(s)
- Christian Ieritano
- Department of Chemistry, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
- Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
- Watermine Innovation, Waterloo, Ontario N0B 2T0, Canada
| | - W Scott Hopkins
- Department of Chemistry, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
- Waterloo Institute for Nanotechnology, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada
- Watermine Innovation, Waterloo, Ontario N0B 2T0, Canada
- Centre for Eye and Vision Research, Hong Kong Science Park, New Territories, 999077, Hong Kong
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Pal N, Saxena N, Mandal A. Synthesis, characterization, and physicochemical properties of a series of quaternary gemini surfactants with different spacer lengths. Colloid Polym Sci 2017. [DOI: 10.1007/s00396-017-4199-1] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Cheng J, Le Saux G, Gao J, Buffeteau T, Battie Y, Barois P, Ponsinet V, Delville MH, Ersen O, Pouget E, Oda R. GoldHelix: Gold Nanoparticles Forming 3D Helical Superstructures with Controlled Morphology and Strong Chiroptical Property. ACS NANO 2017; 11:3806-3818. [PMID: 28358490 DOI: 10.1021/acsnano.6b08723] [Citation(s) in RCA: 75] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
Plasmonic nanoparticles, particularly gold nanoparticles (GNPs) hold a great potential as structural and functional building blocks for three-dimensional (3D) nanoarchitectures with specific optical applications. However, a rational control of their assembly into nanoscale superstructures with defined positioning and overall arrangement still remains challenging. Herein, we propose a solution to this challenge by using as building blocks: (1) nanometric silica helices with tunable handedness and sizes as a matrix and (2) GNPs with diameter varying from 4 to 10 nm to prepare a collection of helical GNPs superstructures (called Goldhelices hereafter). These nanomaterials exhibit well-defined arrangement of GNPs following the helicity of the silica template. Strong chiroptical activity is evidenced by circular dichroism (CD) spectroscopy at the wavelength of the surface plasmon resonance (SPR) of the GNPs with a anisotropy factor (g-factor) of the order of 1 × 10-4, i.e., 10-fold larger than what is typically reported in the literature. Such CD signals were simulated using a coupled dipole method which fit very well the experimental data. The measured signals are 1-2 orders of magnitude lower than the simulated signals, which is explained by the disordered GNPs grafting, the polydispersity of the GNPs, and the dimension of the nanohelices. These Goldhelices based on inorganic templates are much more robust than previously reported organic-based chiroptical nanostructures, making them good candidates for complex hierarchical organization, providing a promising approach for light management and benefits in applications such as circular polarizers, chiral metamaterials, or chiral sensing in the visible range.
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Affiliation(s)
- Jiaji Cheng
- Chimie et Biologie des Membranes et des Nanoobjets (CBMN), CNRS - Université Bordeaux - Bordeaux INP, UMR 5248 , Allée St Hilaire, Bat B14, 33607 Pessac, France
| | - Guillaume Le Saux
- Chimie et Biologie des Membranes et des Nanoobjets (CBMN), CNRS - Université Bordeaux - Bordeaux INP, UMR 5248 , Allée St Hilaire, Bat B14, 33607 Pessac, France
| | - Jie Gao
- Chimie et Biologie des Membranes et des Nanoobjets (CBMN), CNRS - Université Bordeaux - Bordeaux INP, UMR 5248 , Allée St Hilaire, Bat B14, 33607 Pessac, France
| | - Thierry Buffeteau
- Institut des Sciences Moléculaires (ISM), Université Bordeaux-CNRS, UMR 5255 , 351 Cours de la Libération, 33405 Talence, France
| | - Yann Battie
- Laboratoire de Chimie et Physique - Approche Multi-échelles des milieux Complexes (LCP-A2MC), Université de Lorraine , 1 Boulevard Arago, 57078 Metz, France
| | - Philippe Barois
- Centre de Recherche Paul Pascal (CRPP), Université Bordeaux-CNRS-UPR 8641 , Avenue du Dr Albert Schweitzer, 33600 Pessac, France
| | - Virginie Ponsinet
- Centre de Recherche Paul Pascal (CRPP), Université Bordeaux-CNRS-UPR 8641 , Avenue du Dr Albert Schweitzer, 33600 Pessac, France
| | - Marie-Hélène Delville
- Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), CNRS-UPR 9048 , 87 avenue du Dr. A. Schweitzer, 33608 Pessac, France
| | - Ovidiu Ersen
- Institut de Physique et de Chimie des Matériaux de Strasbourg, UMR 7504 CNRS-Université de Strasbourg , 23 Rue du Loess, 67034 Strasbourg, France
| | - Emilie Pouget
- Chimie et Biologie des Membranes et des Nanoobjets (CBMN), CNRS - Université Bordeaux - Bordeaux INP, UMR 5248 , Allée St Hilaire, Bat B14, 33607 Pessac, France
| | - Reiko Oda
- Chimie et Biologie des Membranes et des Nanoobjets (CBMN), CNRS - Université Bordeaux - Bordeaux INP, UMR 5248 , Allée St Hilaire, Bat B14, 33607 Pessac, France
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Sauers RR. Single Electron Transfer and SN2 Reactions: The Importance of Ionization Potential of Nucleophiles. J Chem Theory Comput 2015; 6:602-6. [PMID: 26613295 DOI: 10.1021/ct900611g] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Affiliation(s)
- Ronald R Sauers
- Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903
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Manet S, Karpichev Y, Dedovets D, Oda R. Effect of Hofmeister and alkylcarboxylate anionic counterions on the Krafft temperature and melting temperature of cationic gemini surfactants. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2013; 29:3518-3526. [PMID: 23346886 DOI: 10.1021/la304341x] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/01/2023]
Abstract
The effect of counterions was investigated to probe the principal ionic effects on the solubility in water and melting behavior of cationic gemini surfactants. We focused on two types of counterions: (1) small inorganic counterions that are typically taken from the Hofmeister series were studied to focus on the effect of ion type and (2) n-alkylcarboxylate counterions were studied to focus on the effect of the hydrophobicity of counterions. The Krafft temperature (Tk) and melting temperature (Tm) were obtained by conductivity measurements, calorimetric measurements, and optical microscopy observation. The results clearly indicate that Tk, which represents the solubility of surfactants, is not determined by a single parameter of ions such as the hydration free energy, as is too often assumed, but rather by the combined effects between the hydrophobicity of anions associated with other effects such as the polarizability, dehydrated ion size, and ionic morphology. In parallel, our observation demonstrated that all of the surfactants showed a transition from a crystalline phase to a thermotropic liquid-crystalline phase at around ca. 70 °C, which transformed to an isotropic liquid phase at around ca. 150 °C, and that the transition temperatures depended strongly on the counterion type. The counterion effects on the solubilization and melting behaviors were then compared with micellization properties that have been reported previously. These results provide new insight into understanding the effect of ions on the delicate balance of forces controlling the solution properties and aggregate morphology of charged amphiphilic molecules. Specifically, the solubilization properties of these cationic surfactants with various counterions were determined mainly by the subtle interplay between the hydration of counterions and the dissociation energies (stability of crystallinity) of the ion pair.
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Affiliation(s)
- Sabine Manet
- UMR 5248 CBMN, CNRS-Université de Bordeaux, Institut Européen de Chimie et Biologie, 2 rue Robert Escarpit, F-33607 Pessac, France
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Gargouri M, Chaudière J, Manigand C, Maugé C, Bathany K, Schmitter JM, Gallois B. The epimerase activity of anthocyanidin reductase from Vitis vinifera and its regiospecific hydride transfers. Biol Chem 2010; 391:219-227. [PMID: 20030585 DOI: 10.1515/bc.2010.015] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Anthocyanidin reductase (ANR) from Vitis vinifera catalyzes an NADPH-dependent double reduction of anthocyanidins producing a mixture of (2S,3R)- and (2S,3S)-flavan-3-ols. At pH 7.5 and 30 degrees C, the first hydride transfer to anthocyanidin is irreversible, and no intermediate is released during catalysis. ANR reverse activity was assessed in the presence of excess NADP(+). Analysis of products by reverse phase and chiral phase HPLC demonstrates that ANR acts as a flavan-3-ol C(3)-epimerase under such conditions, but this is only observed with 2R-flavan-3-ols, not with 2S-flavan-3-ols produced by the enzyme in the forward reaction. In the presence of deuterated coenzyme 4S-NADPD, ANR transforms anthocyanidins into dideuterated flavan-3-ols. The regiospecificity of deuterium incorporation into catechin and afzelechin - derived from cyanidin and pelargonidin, respectively - was analyzed by liquid chromatography coupled with electro- spray ionization-tandem mass spectrometry (LC/ESI-MS/MS), and it was found that deuterium was always incorporated at C(2) and C(4). We conclude that C(3)-epimerization should be achieved by tautomerization between the two hydride transfers and that this produces a quinone methide intermediate which serves as C(4) target of the second hydride transfer, thereby avoiding any stereospecific modification of carbon 3. The inversion of C(2) stereochemistry required for 'reverse epimerization' suggests that the 2S configuration induces an irreversible product dissociation.
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Affiliation(s)
- Mahmoud Gargouri
- Chimie et Biologie des Membranes et des Nanoobjets UMR CNRS 5248, Bâtiment B8, Avenue des Facultés, Université Bordeaux 1, F-33405 Talence Cedex, France.,Laboratoire de Physiologie Moléculaire des Plantes, Centre de Biotechnologie de Borj-Cedria, B.P. 901, 2050 Hamman-Lif, Tunisia
| | - Jean Chaudière
- Chimie et Biologie des Membranes et des Nanoobjets UMR CNRS 5248, Bâtiment B8, Avenue des Facultés, Université Bordeaux 1, F-33405 Talence Cedex, France
| | - Claude Manigand
- Chimie et Biologie des Membranes et des Nanoobjets UMR CNRS 5248, Bâtiment B8, Avenue des Facultés, Université Bordeaux 1, F-33405 Talence Cedex, France
| | - Chloé Maugé
- Chimie et Biologie des Membranes et des Nanoobjets UMR CNRS 5248, Bâtiment B8, Avenue des Facultés, Université Bordeaux 1, F-33405 Talence Cedex, France
| | - Katell Bathany
- Chimie et Biologie des Membranes et des Nanoobjets UMR CNRS 5248, Bâtiment B8, Avenue des Facultés, Université Bordeaux 1, F-33405 Talence Cedex, France
| | - Jean-Marie Schmitter
- Chimie et Biologie des Membranes et des Nanoobjets UMR CNRS 5248, Bâtiment B8, Avenue des Facultés, Université Bordeaux 1, F-33405 Talence Cedex, France
| | - Bernard Gallois
- Chimie et Biologie des Membranes et des Nanoobjets UMR CNRS 5248, Bâtiment B8, Avenue des Facultés, Université Bordeaux 1, F-33405 Talence Cedex, France
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Chen X, Walthall DA, Brauman JI. Geometry dependence of the ring-opening E2 reaction in lactones. J Phys Chem A 2010; 114:1392-7. [PMID: 19860403 DOI: 10.1021/jp906968d] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Gas phase bimolecular elimination reactions (E2) of lactones, with and without alkyl substitution on the omega carbon, have been studied. The comparison between the substituted and corresponding unsubstituted lactones reveals, without complications from ring strain, the effect of geometric distortion from the periplanar geometry preferred for E2 reactions. The four- and five-membered ring lactones show a significant effect from the distortion, while the six- and seven-membered rings show relatively little. The geometric distortion is clearly much more important than the ring strain. The kinetic energy dependence of the E2 reaction as well as the proton transfer reaction between fluoride and a partially deuterated delta-valerolactone has also been investigated.
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Affiliation(s)
- Xin Chen
- Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA
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