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Salvitti C, Chiarotto I, Pepi F, Troiani A. Charge-Tagged N-Heterocyclic Carbenes (NHCs): Revealing the Hidden Side of NHC-Catalysed Reactions through Electrospray Ionization Mass Spectrometry. Chempluschem 2020; 86:209-223. [PMID: 33252194 DOI: 10.1002/cplu.202000656] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 11/16/2020] [Indexed: 01/08/2023]
Abstract
N-heterocyclic carbenes (NHCs) are key intermediates in a variety of chemical reactions. Owing to their transient nature, the interception and characterization of these reactive species have always been challenging. Similarly, the study of reaction mechanisms in which carbenes act as catalysts is still an active research field. This Minireview describes the contribution of electrospray ionization mass spectrometry (ESI-MS) to the detection of charge-tagged NHCs resulting from the insertion of an ionic group into the molecular scaffold. The use of different mass spectrometric techniques, combined with the charge-tagging strategy, allowed clarification of the involvement of NHCs in archetypal reactions and the study of their intrinsic chemistry.
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Affiliation(s)
- Chiara Salvitti
- Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Università di Roma, P.le Aldo Moro 5, Rome, Italy
| | - Isabella Chiarotto
- Dipartimento di Scienze di Base e Applicate per l'Ingegneria, Sapienza Università di Roma, Via Castro Laurenziano 7, Rome, Italy
| | - Federico Pepi
- Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Università di Roma, P.le Aldo Moro 5, Rome, Italy
| | - Anna Troiani
- Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Università di Roma, P.le Aldo Moro 5, Rome, Italy
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Pandit SA, Bhat SA, Rather MA, Ingole PP, Bhat MA. Mechanistic insight into the electrocatalytic performance of reduced graphene oxide supported palladium, silver and palladium-silver nanodeposits toward electro-dehalogenation of halocarbons in room temperature ionic liquids. Phys Chem Chem Phys 2020; 22:16985-16997. [PMID: 32676629 DOI: 10.1039/d0cp01932a] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Herein, we report the results from our extensive voltammetric investigations designed to explore, assess and explain the electrocatalytic performance of reduced graphene oxide supported metal nano-deposits toward the electro-dehalogenation of halocarbons in room temperature ionic liquids (RTILs). Specifically, we investigated the electro-reductive dechlorination of the model halocarbon, carbon tetrachloride over glassy carbon electrode (GCE) and palladium-graphene (Pd-Gr), silver-graphene (Ag-Gr) and palladium-silver-graphene (PdAg-Gr) nanocomposites in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][NTf2]). Analysis of the voltammetric data in light of Marcus-Hush formulation reveals that the electro-reductive cleavage of the C-Cl bond of CCl4 over GCE in [BMIM][NTf2] follows a sticky dissociative electron transfer (SDET) pathway. The significantly stronger interaction energy between electrogenerated Cl- and CCl3˙ (radical) fragments in RTILs makes electroreduction of CCl4 in [BMIM][NTf2] much easier than in organic solvents. The activation-driving force relationship for electro-catalytic dechlorination of CCl4 over Pd-Gr was observed to follow a modified sticky dissociative electron transfer model wherein apart from the ion-radical interaction, the adsorptive interaction of chlorinated species with the electrocatalytic surface needs to be taken into consideration to account for the apparent activation energy-driving force dependence. Interestingly the activation energy-driving force relationships for the electroreduction of CCl4 over Ag-Gr and PdAg-Gr were observed to fit a modified stepwise ET (MSET) pathway. In the MSET pathway, the adsorption and the implied free energy change of the electroreducible halocarbon significantly alter the solvent re-organization energy and the inherent barrier for the heterogeneous ET process. The adsorptive interaction and hence the electrocatalytic performance of PdAg-Gr were observed to be more than that observed for Ag-Gr. This is attributed to the Ag to Pd charge transfer in the PdAg-Gr nanodeposits. Our results besides underlining the positive influence of RTILs in facilitating the electroreductive detoxification of halocarbons, very well establish the mechanistic basis for the electrocatalytic performance of graphene based nanodeposits toward electrodehalogenation of halocarbons.
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Gehrke S, Hollóczki O. N-Heterocyclic Carbene Organocatalysis: With or Without Carbenes? Chemistry 2020; 26:10140-10151. [PMID: 32608090 PMCID: PMC7496998 DOI: 10.1002/chem.202002656] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2020] [Revised: 06/26/2020] [Indexed: 11/18/2022]
Abstract
In this work the mechanism of the aldehyde umpolung reactions, catalyzed by azolium cations in the presence of bases, was studied through computational methods. Next to the mechanism established by Breslow in the 1950s that takes effect through the formation of a free carbene, we have suggested that these processes can follow a concerted asynchronous path, in which the azolium cation directly reacts with the substrate, avoiding the formation of the carbene intermediate. We hereby show that substituting the azolium cation, and varying the base or the substrate do not affect the preference for the concerted reaction mechanism. The concerted path was found to exhibit low barriers also for the reactions of thiamine with model substrates, showing that this path might have biological relevance. The dominance of the concerted mechanism can be explained through the specific structure of the key transition state, avoiding the liberation of the highly reactive, and thus unstable carbene lone pair, whereas activating the substrate through hydrogen-bonding interactions. Polar and hydrogen-bonding solvents, as well as the presence of the counterions of the azolium salts facilitate the reaction through carbenes, bringing the barriers of the two reaction mechanisms closer, in many cases making the concerted path less favorable. Thus, our data show that by choosing the exact components in a reaction, the mechanism can be switched to occur with or without carbenes.
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Affiliation(s)
- Sascha Gehrke
- Mulliken Center for Theoretical ChemistryUniversity of BonnBeringstr. 4+653115BonnGermany
| | - Oldamur Hollóczki
- Mulliken Center for Theoretical ChemistryUniversity of BonnBeringstr. 4+653115BonnGermany
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de Oliveira Marcionilio SML, Crisafulli R, Medeiros GA, de Sousa Tonhá M, Garnier J, Neto BAD, Linares JJ. Influence of hydrodynamic conditions on the degradation of 1-butyl-3-methylimidazolium chloride solutions on boron-doped diamond anodes. CHEMOSPHERE 2019; 224:343-350. [PMID: 30826704 DOI: 10.1016/j.chemosphere.2019.02.128] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/23/2018] [Revised: 02/20/2019] [Accepted: 02/21/2019] [Indexed: 06/09/2023]
Abstract
This study assessed the influence of hydrodynamic conditions on the degradation process of 1-butyl-3-methylimidazolium chloride (BMImCl) solution on a boron-doped diamond anode in a filter-type electrochemical reactor configuration. The results show that this parameter did not significantly affect this process when operating in the laminar regime. However, in the transition regime (Re ≥ 2000), higher flow rates resulted in a faster removal of BMImCl and total organic carbon, making the process more efficient. Following BMImCl degradation, nitrates were generated at the cathode, then reduced at the cathode to ammonium; combination with free chloride produced at the anode led to the transformation of chloride into combined chlorine forms instead of more toxic oxianions such as chlorate and perchlorate. Thus, the flow rate can be a key parameter for defining operating conditions in which the target BMImCl is more effectively degraded with reduced generation of undesirable secondary products.
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Affiliation(s)
| | - Rudy Crisafulli
- Instituto de Química, Universidade de Brasília, Campus Darcy Ribeiro, 70910-900, Brasília, DF, Brazil
| | - Gisele A Medeiros
- Instituto de Química, Universidade de Brasília, Campus Darcy Ribeiro, 70910-900, Brasília, DF, Brazil
| | - Myller de Sousa Tonhá
- Laboratório de Geoquímica, Instituto de Geociências, Universidade de Brasília, Campus Darcy Ribeiro, 70910-900, Brasília, DF, Brazil
| | - Jeremie Garnier
- Laboratório de Geoquímica, Instituto de Geociências, Universidade de Brasília, Campus Darcy Ribeiro, 70910-900, Brasília, DF, Brazil
| | - Brenno A D Neto
- Instituto de Química, Universidade de Brasília, Campus Darcy Ribeiro, 70910-900, Brasília, DF, Brazil
| | - José J Linares
- Instituto de Química, Universidade de Brasília, Campus Darcy Ribeiro, 70910-900, Brasília, DF, Brazil.
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Gehrke S, Hollóczki O. Hydrogen Bonding of N‐Heterocyclic Carbenes in Solution: Mechanisms of Solvent Reorganization. Chemistry 2018; 24:11594-11604. [DOI: 10.1002/chem.201802286] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2018] [Revised: 06/07/2018] [Indexed: 11/05/2022]
Affiliation(s)
- Sascha Gehrke
- Mulliken Center for Theoretical ChemistryUniversity of Bonn Beringstr. 4+6 53115 Bonn Germany
- Max Planck Institute for Chemical Energy Conversion Stiftstrasse 34-36 45470 Muelheim an der Ruhr Germany
| | - Oldamur Hollóczki
- Mulliken Center for Theoretical ChemistryUniversity of Bonn Beringstr. 4+6 53115 Bonn Germany
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Affiliation(s)
- Navjeet Kaur
- Department of Chemistry, Banasthali University, Banasthali, Rajasthan, India
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Dunn MH, Konstandaras N, Cole ML, Harper JB. Targeted and Systematic Approach to the Study of pKa Values of Imidazolium Salts in Dimethyl Sulfoxide. J Org Chem 2017. [DOI: 10.1021/acs.joc.7b00716] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Michelle H. Dunn
- School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Nicholas Konstandaras
- School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Marcus L. Cole
- School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia
| | - Jason B. Harper
- School of Chemistry, University of New South Wales, Sydney, New South Wales 2052, Australia
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8
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Advances in the Knowledge of N-Heterocyclic Carbenes Properties. The Backing of the Electrochemical Investigation. Catalysts 2016. [DOI: 10.3390/catal6110178] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
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9
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Axelsson A, Ta L, Sundén H. Direct Highly Regioselective Functionalization of Carbohydrates: A Three-Component Reaction Combining the Dissolving and Catalytic Efficiency of Ionic Liquids. European J Org Chem 2016. [DOI: 10.1002/ejoc.201600536] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Anton Axelsson
- Chemistry and Chemical Engineering; Chalmers University of Technology; Kemivägen 10 41296 Göteborg Sweden
| | - Linda Ta
- Chemistry and Chemical Engineering; Chalmers University of Technology; Kemivägen 10 41296 Göteborg Sweden
| | - Henrik Sundén
- Chemistry and Chemical Engineering; Chalmers University of Technology; Kemivägen 10 41296 Göteborg Sweden
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Butler BJ, Thomas DS, Hook JM, Harper JB. NMR spectroscopy to follow reaction progress in ionic liquids. MAGNETIC RESONANCE IN CHEMISTRY : MRC 2016; 54:423-428. [PMID: 25287592 DOI: 10.1002/mrc.4161] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/08/2014] [Revised: 09/05/2014] [Accepted: 09/15/2014] [Indexed: 06/03/2023]
Abstract
In order to understand reaction outcomes in ionic liquids, it is crucial to be able to follow the progress of these reactions. This review highlights the advantages of NMR spectroscopy over other analytical techniques in following reaction progress in ionic liquids, particularly addressing the practical aspects of the methodology and highlighting the range of processes that can be readily followed. Copyright © 2014 John Wiley & Sons, Ltd.
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Affiliation(s)
- Bradley J Butler
- School of Chemistry, University of New South Wales (UNSW), Sydney, NSW, 2052, Australia
| | - Donald S Thomas
- Nuclear Magnetic Resonance Facility, Mark Wainwright Analytical Centre, University of New South Wales (UNSW), Sydney, NSW, 2052, Australia
| | - James M Hook
- Nuclear Magnetic Resonance Facility, Mark Wainwright Analytical Centre, University of New South Wales (UNSW), Sydney, NSW, 2052, Australia
| | - Jason B Harper
- School of Chemistry, University of New South Wales (UNSW), Sydney, NSW, 2052, Australia
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Butler BJ, Harper JB. The effect of the structure of the cation of an ionic liquid on the rate of reaction at a phosphorus centre. J PHYS ORG CHEM 2016. [DOI: 10.1002/poc.3554] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Bradley J. Butler
- School of Chemistry University of New South Wales, UNSW Sydney 2052 Australia
| | - Jason B. Harper
- School of Chemistry University of New South Wales, UNSW Sydney 2052 Australia
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Hollóczki O. Unveiling the peculiar hydrogen bonding behavior of solvated N-heterocyclic carbenes. Phys Chem Chem Phys 2016; 18:126-40. [DOI: 10.1039/c5cp05369b] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
After fitting a molecular mechanical force field for imidazol-2-ylidenes, MD simulations revealed carbene–carbene and three-center hydrogen bonds of carbenes. The practical importance of these structures is also highlighted.
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Affiliation(s)
- Oldamur Hollóczki
- Mulliken Center for Theoretical Chemistry
- University of Bonn
- D-53115 Bonn
- Germany
- Department of Inorganic and Analytical Chemistry
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13
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Gehrke S, Hollóczki O. A molecular mechanical model for N-heterocyclic carbenes. Phys Chem Chem Phys 2016; 18:22070-80. [PMID: 27426687 DOI: 10.1039/c6cp02624a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this work a set of force fields for nine synthetically relevant and/or structurally interesting N-heterocyclic carbenes is presented, allowing facile substitution and the simulation of numerous carbene catalysts in solution by classical MD.
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Affiliation(s)
- Sascha Gehrke
- Mulliken Center for Theoretical Chemistry
- University of Bonn
- D-53115 Bonn
- Germany
- Max Planck Institute for Chemical Energy Conversion
| | - Oldamur Hollóczki
- Mulliken Center for Theoretical Chemistry
- University of Bonn
- D-53115 Bonn
- Germany
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Stability and organocatalytic efficiency of N-heterocyclic carbenes electrogenerated in organic solvents from imidazolium ionic liquids. Electrochim Acta 2015. [DOI: 10.1016/j.electacta.2014.11.135] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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15
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Butler BJ, Harper JB. The effect of an ionic liquid on the rate of reaction at a phosphorus centre. NEW J CHEM 2015. [DOI: 10.1039/c4nj01224k] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Rate constant of a substitution at phosphorus varies with amount of ionic liquid present; enthalpic benefit offsets entropic cost.
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Affiliation(s)
- Bradley J. Butler
- School of Chemistry
- University of New South Wales
- UNSW Sydney 2052
- Australia
| | - Jason B. Harper
- School of Chemistry
- University of New South Wales
- UNSW Sydney 2052
- Australia
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Ta L, Axelsson A, Bijl J, Haukka M, Sundén H. Ionic liquids as precatalysts in the highly stereoselective conjugate addition of α,β-unsaturated aldehydes to chalcones. Chemistry 2014; 20:13889-93. [PMID: 25201607 DOI: 10.1002/chem.201404288] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Indexed: 11/06/2022]
Abstract
Imidazolium-based ionic liquids (ILs) serve both as recyclable reaction media and as precatalysts for the N-heterocyclic carbene-catalyzed conjugate addition of α,β-unsaturated aldehydes to chalcones. The reaction produces a broad scope of 1,6-ketoesters incorporating an anti-diphenyl moiety in high yields and with high stereoselectivity. In recycling experiments, the IL can be reused up to five times with retained reactivity and selectivity. Moreover, the 1,6-ketoesters form self-assembled organogels in aliphatic hydrocarbons. The reaction protocol is robust, easily operated, scalable and highly functionalized compounds can be obtained from inexpensive and readily accessible starting materials.
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Affiliation(s)
- Linda Ta
- Chemistry and Biological Engineering, Chalmers University of Technology, Kemivägen 10, 412 96 Gothenburg (Sweden)
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Thomas M, Brehm M, Hollóczki O, Kirchner B. How Can a Carbene be Active in an Ionic Liquid? Chemistry 2013; 20:1622-9. [DOI: 10.1002/chem.201303329] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2013] [Revised: 11/14/2013] [Indexed: 11/10/2022]
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Tanaka K, Chujo Y. Chemicals-Inspired Biomaterials: Developing Biomaterials Inspired by Material Science Based on POSS. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2013. [DOI: 10.1246/bcsj.20130182] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Affiliation(s)
- Kazuo Tanaka
- Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University
| | - Yoshiki Chujo
- Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University
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Jeon JH, Tanaka K, Chujo Y. POSS fillers for modulating the thermal properties of ionic liquids. RSC Adv 2013. [DOI: 10.1039/c2ra22683a] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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Tanner EEL, Hawker RR, Yau HM, Croft AK, Harper JB. Probing the importance of ionic liquid structure: a general ionic liquid effect on an SNAr process. Org Biomol Chem 2013; 11:7516-21. [DOI: 10.1039/c3ob41634h] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Tanner EEL, Yau HM, Hawker RR, Croft AK, Harper JB. Does the cation really matter? The effect of modifying an ionic liquid cation on an SN2 process. Org Biomol Chem 2013; 11:6170-5. [DOI: 10.1039/c3ob41038b] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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22
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Keaveney ST, Harper JB. Towards reaction control using an ionic liquid: biasing outcomes of reactions of benzyl halides. RSC Adv 2013. [DOI: 10.1039/c3ra42820f] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
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