1
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Nucleophilic Reactions Using Alkali Metal Fluorides Activated by Crown Ethers and Derivatives. Catalysts 2023. [DOI: 10.3390/catal13030479] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/02/2023] Open
Abstract
We review crown ether-facilitated nucleophilic reactions using metal salts, presenting the studies using kinetic measurements and quantum chemical methods. We focus on the mechanistic features, specifically on the contact ion-pair (CIP) mechanism of metal salts for nucleophilic processes promoted by crown ethers and derivatives. Experimental verification of the CIP form of the metal salt CsF complexed with [18-Crown-6] by H-NMR spectroscopy is described. The use of chiral crown ethers and derivatives for enantioselective nucleophilic processes is also discussed.
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2
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de Cózar A. Diastereoselectivity on Intramolecular Alder-ene Reaction of 1,6-Dienes. Chemphyschem 2022; 23:e202200377. [PMID: 35942565 PMCID: PMC10087545 DOI: 10.1002/cphc.202200377] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Revised: 08/07/2022] [Indexed: 01/04/2023]
Abstract
A detailed computational study of the intramolecular Alder-ene reaction of different 1,6-dienes at M06-2X(PCM)/TZ2P level of theory has been performed. We want to understand the influence of enophile-geminal substitution pattern in the cis : trans selectivity of the cyclization process. Our analysis of the reaction coordinate by means of activation strain model of chemical reactivity (ASM-distortion interaction model) reveals that the cis-selectivity observed for unactivated reagents is related with high stabilizing orbital interaction and lower strain energy, consequence of an early transition structure. On the other hand, the presence of activating groups increases the asynchronicity of the transition structures and reduces the activation barrier due to more stabilizing orbital and electrostatic interactions, favoring trans-selectivity.
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Affiliation(s)
- Abel de Cózar
- Departamento de Química Orgánica I, Facultad de Química, Universidad del País Vasco and Donostia International Physics Center (DIPC) P. K. 1072, 20018, San Sebastián-Donostia, Spain.,IKERBASQUE, Basque Foundation for Science, Plaza Euskadi 5, 48009, Bilbao, Spain
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3
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Hernández-Mancera JP, Rojas-Valencia N, Núñez-Zarur F. Rationalizing the Substituent Effects in Diels-Alder Reactions of Triazolinediones with Anthracene. J Phys Chem A 2022; 126:6657-6667. [PMID: 36122186 DOI: 10.1021/acs.jpca.2c04970] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this work we tackle the problem of the substituent effects in the Diels-Alder cycloadditions between triazolinediones (TADs) and anthracene. Experiments showed that aryl TADs substituted with electron-withdrawing groups (EWG) are more reactive than those substituted with electron-donating (EDG) or alkyl groups. However, the molecular origin of this preference is not yet understood. By a combination of methods including the activation strain model (ASM), energy decomposition analysis (EDA), molecular orbital (MO) theory, and conceptual density functional theory (CDFT), we disclosed the substituent effects of TADs. First, ASM/EDA analysis revealed that the reactivity of alkyl and aryl-substituted TADs is controlled by interaction energies, ΔEint, which are ultimately defined by orbital interactions between frontier molecular orbitals. Moreover, alkyl-TADs are also controlled by the extent of strain at the transition state. The MO analysis suggested that the rate acceleration for EWG-substituted TADs is due to a more favorable orbital interaction between the HOMO of anthracene and the LUMO of the TADs, which is corroborated by calculations of charge transfer at the transition states. From CDFT, the chemical potential of anthracene is higher than those of TADs, indicating a flow of electron density from anthracene to TADs, in agreement with the results from the electrophilicity index.
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Affiliation(s)
| | - Natalia Rojas-Valencia
- Facultad de Ciencias Básicas, Universidad de Medellín, Carrera 87 no. 30-65, 050026 Medellín, Colombia
| | - Francisco Núñez-Zarur
- Facultad de Ciencias Básicas, Universidad de Medellín, Carrera 87 no. 30-65, 050026 Medellín, Colombia
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4
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García-Aznar P, Escorihuela J. Computational insights into the inverse electron-demand Diels-Alder reaction of norbornenes with 1,2,4,5-tetrazines: norbornene substituents' effects on the reaction rate. Org Biomol Chem 2022; 20:6400-6412. [PMID: 35876298 DOI: 10.1039/d2ob01121b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The study of the reaction rates and mechanism of click chemistry reactions still remains an interesting challenge in organic chemistry. In this regard, the inverse electron demand Diels-Alder (IEDDA) reaction represents a promising metal-free alternative with enhanced reaction rates compared to other reactions of the click chemistry toolbox. Among the different types of dienophiles used in the IEDDA reactions, norbornenes have been widely used given their high stability and fast reaction rates. The inverse electron-demand Diels Alder reaction of 3,6-dipyridin-2-yl-1,2,4,5-tetrazine with a series of norbornene derivatives was studied with quantum mechanical calculations at the M06-2X/6-311+G(d,p) level of theory. The theoretical predictions were confirmed with the experimental data and analyzed with the use of the distortion/interaction model. The obtained results will help in obtaining a better understanding of the factors that affect the relative cycloaddition rates of norbornenes with tetrazines, which are crucial for selectively tuning their efficacy.
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Affiliation(s)
- Pablo García-Aznar
- Departamento de Química Orgánica, Facultad de Farmacia, Universitat de València, Avda. Vicente Andrés Estellés, s/n, Burjassot 46100, València, Spain.
| | - Jorge Escorihuela
- Departamento de Química Orgánica, Facultad de Farmacia, Universitat de València, Avda. Vicente Andrés Estellés, s/n, Burjassot 46100, València, Spain.
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5
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Oh Y, Yun W, Lee S, Kim DW. Kinetics and Quantum Chemical Analysis of Intramolecular S
N
2 Reactions by Using Metal Salts and Promoted by Crown Ethers: Contact Ion Pair vs. Separated Nucleophile Mechanism. ChemistrySelect 2022. [DOI: 10.1002/slct.202104431] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Affiliation(s)
- Young‐Ho Oh
- Department of Applied Chemistry Kyung Hee University 1732, Deogyeong-daero, Giheung-gu Yongin-si Gyeonggi-do 17104, Republic of Korea
| | - Wonhyuk Yun
- Department of Chemistry and Chemical Engineering Inha University 100 Inha-ro, Nam-gu Incheon 402-751, Republic of Korea
| | - Sungyul Lee
- Department of Applied Chemistry Kyung Hee University 1732, Deogyeong-daero, Giheung-gu Yongin-si Gyeonggi-do 17104, Republic of Korea
| | - Dong Wook Kim
- Department of Chemistry and Chemical Engineering Inha University 100 Inha-ro, Nam-gu Incheon 402-751, Republic of Korea
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6
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Savoo N, Rhyman L, Ramasami P. Theoretical study of a derivative of chlorophosphine with aliphatic and aromatic Grignard reagents: S N2@P or the novel S N2@Cl followed by S N2@C? RSC Adv 2022; 12:9130-9138. [PMID: 35424871 PMCID: PMC8985194 DOI: 10.1039/d2ra00258b] [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] [Received: 01/13/2022] [Accepted: 03/15/2022] [Indexed: 11/21/2022] Open
Abstract
The proposed SN2 reactions of a hindered organophosphorus reactant with aliphatic and aromatic nucleophiles [Ye et al., Org. Lett., 2017, 19, 5384–5387] were studied theoretically in order to explain the observed stereochemistry of the products.
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Affiliation(s)
- Nandini Savoo
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit 80837, Mauritius
| | - Lydia Rhyman
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit 80837, Mauritius
- Centre for Natural Product Research, Department of Chemical Sciences, University of Johannesburg, Doornfontein Campus, Johannesburg 2028, South Africa
| | - Ponnadurai Ramasami
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit 80837, Mauritius
- Centre for Natural Product Research, Department of Chemical Sciences, University of Johannesburg, Doornfontein Campus, Johannesburg 2028, South Africa
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7
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Li W, Lu Z, Hammond GB, Xu B. Unbalanced-Ion-Pair-Catalyzed Nucleophilic Fluorination Using Potassium Fluoride. Org Lett 2021; 23:9640-9644. [PMID: 34851641 DOI: 10.1021/acs.orglett.1c03887] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
An unbalanced ion pair promoter (e.g., tetrabutylammonium sulfate), consisting of a bulky and charge-delocalized cation and a small and charge-localized anion, greatly accelerates nucleophilic fluorinations using easy handling KF. We also successfully converted an inexpensive and commercially available ion-exchange resin to the polymer-supported ion pair promoter (A26-SO42-), which could be reused after filtration. Moreover, A26-SO42- can be used in continuous flow conditions. In our conditions, water is well-tolerated.
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Affiliation(s)
- Wangbing Li
- Key Laboratory of Science and Technology of Eco-Textiles, Ministry of Education, College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, 201620, China
| | - Zhichao Lu
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Gerald B Hammond
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Bo Xu
- Key Laboratory of Science and Technology of Eco-Textiles, Ministry of Education, College of Chemistry, Chemical Engineering and Biotechnology, Donghua University, Shanghai, 201620, China
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8
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Otsuka M, Miyaguchi H. Theoretical evaluation of the hydrolysis of conventional nerve agents and novichok agents. Chem Phys Lett 2021. [DOI: 10.1016/j.cplett.2021.139116] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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9
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Vermeeren P, Hamlin TA, Bickelhaupt FM. Chemical reactivity from an activation strain perspective. Chem Commun (Camb) 2021; 57:5880-5896. [PMID: 34075969 PMCID: PMC8204247 DOI: 10.1039/d1cc02042k] [Citation(s) in RCA: 57] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Accepted: 05/25/2021] [Indexed: 12/14/2022]
Abstract
Chemical reactions are ubiquitous in the universe, they are at the core of life, and they are essential for industrial processes. The drive for a deep understanding of how something occurs, in this case, the mechanism of a chemical reaction and the factors controlling its reactivity, is intrinsically valuable and an innate quality of humans. The level of insight and degree of understanding afforded by computational chemistry cannot be understated. The activation strain model is one of the most powerful tools in our arsenal to obtain unparalleled insight into reactivity. The relative energy of interacting reactants is evaluated along a reaction energy profile and related to the rigidity of the reactants' molecular structure and the strength of the stabilizing interactions between the deformed reactants: ΔE(ζ) = ΔEstrain(ζ) + ΔEint(ζ). Owing to the connectedness between the activation strain model and Kohn-Sham molecular orbital theory, one is able to obtain a causal relationship between both the sterics and electronics of the reactants and their mutual reactivity. Only when this is accomplished one can eclipse the phenomenological explanations that are commonplace in the literature and textbooks and begin to rationally tune and optimize chemical transformations. We showcase how the activation strain model is the ideal tool to elucidate fundamental organic reactions, the activation of small molecules by metallylenes, and the cycloaddition reactivity of cyclic diene- and dipolarophiles.
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Affiliation(s)
- Pascal Vermeeren
- Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
| | - Trevor A Hamlin
- Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands.
| | - F Matthias Bickelhaupt
- Department of Theoretical Chemistry, Amsterdam Institute of Molecular and Life Sciences (AIMMS), Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV Amsterdam, The Netherlands. and Institute for Molecules and Materials (IMM), Radboud University, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands
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10
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Inter- and Intra-Molecular Organocatalysis of S N2 Fluorination by Crown Ether: Kinetics and Quantum Chemical Analysis. Molecules 2021; 26:molecules26102947. [PMID: 34063489 PMCID: PMC8156096 DOI: 10.3390/molecules26102947] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Revised: 05/05/2021] [Accepted: 05/12/2021] [Indexed: 11/29/2022] Open
Abstract
We present the intra- and inter-molecular organocatalysis of SN2 fluorination using CsF by crown ether to estimate the efficacy of the promoter and to elucidate the reaction mechanism. The yields of intramolecular SN2 fluorination of the veratrole substrates are measured to be very small (<1% in 12 h) in the absence of crown ether promoters, whereas the SN2 fluorination of the substrate possessing a crown ether unit proceeds to near completion (~99%) in 12 h. We also studied the efficacy of intermolecular rate acceleration by an independent promoter 18-crown-6 for comparison. We find that the fluorinating yield of a veratrole substrate (leaving group = −OMs) in the presence of 18-crown-6 follows the almost identical kinetic course as that of intramolecular SN2 fluorination, indicating the mechanistic similarity of intra- and inter-molecular organocatalysis of the crown ether for SN2 fluorination. The calculated relative Gibbs free energies of activation for these reactions, in which the crown ether units act as Lewis base promoters for SN2 fluorination, are in excellent agreement with the experimentally measured yields of fluorination. The role of the metal salt CsF is briefly discussed in terms of whether it reacts as a contact ion pair or as a “free” nucleophile F−.
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11
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Otsuka M, Miyaguchi H. Evaluation of the possibility of binary synthesis of VX by theoretical calculation. Chem Phys Lett 2020. [DOI: 10.1016/j.cplett.2020.137808] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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12
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Transition-State Expansion: A Quantitative Model for Counterion Effects in Ionic Reactions. iScience 2020; 23:101593. [PMID: 33083752 PMCID: PMC7554029 DOI: 10.1016/j.isci.2020.101593] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2020] [Revised: 08/03/2020] [Accepted: 09/17/2020] [Indexed: 11/21/2022] Open
Abstract
Ionic reactions are the most common reactions used in chemical synthesis. In relatively low dielectric constant solvents (e.g., dichloromethane, toluene), ions usually exist as ion pairs. Despite the importance of counterions, a quantitative description of how the paired 'counterion' affects the reaction kinetic is still elusive. We introduce a general and quantitative model, namely transition-state expansion (TSE), that describes how the size of a counterion affects the transition-state structure and the kinetics of an ionic reaction. This model could rationalize the counterion effects in nucleophilic substitutions and gold-catalyzed enyne cycloisomerizations. A quantitative model for counterion effects was introduced 'Transition State Expansion' was used to describes how the size of a counterion affects the kinetics
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13
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Bettens T, Alonso M, De Proft F, Hamlin TA, Bickelhaupt FM. Ambident Nucleophilic Substitution: Understanding Non-HSAB Behavior through Activation Strain and Conceptual DFT Analyses. Chemistry 2020; 26:3884-3893. [PMID: 31957943 PMCID: PMC7154642 DOI: 10.1002/chem.202000272] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Indexed: 01/31/2023]
Abstract
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 SN 2 reaction channels of archetypal ambident nucleophiles CN- , OCN- , and SCN- with CH3 Cl (SN 2@C) and SiH3 Cl (SN 2@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 SN 2@C and SN 2@Si reactions. We provide simple rules for predicting the ambident reactivity of nucleophiles based on our Kohn-Sham molecular orbital analysis.
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Affiliation(s)
- Tom Bettens
- Eenheid Algemene Chemie (ALGC)Vrije Universiteit BrusselPleinlaan 21050BrusselsBelgium
| | - Mercedes Alonso
- Eenheid Algemene Chemie (ALGC)Vrije Universiteit BrusselPleinlaan 21050BrusselsBelgium
| | - Frank De Proft
- Eenheid Algemene Chemie (ALGC)Vrije Universiteit BrusselPleinlaan 21050BrusselsBelgium
| | - Trevor A. Hamlin
- Department of Theoretical ChemistryAmsterdam Institute of Molecular and Life Sciences (AIMMS)Amsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081HVAmsterdamThe Netherlands
| | - F. Matthias Bickelhaupt
- Department of Theoretical ChemistryAmsterdam Institute of Molecular and Life Sciences (AIMMS)Amsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081HVAmsterdamThe Netherlands
- Institute for Molecules and Materials (IMM)Radboud University NijmegenHeyendaalseweg 1356525AJNijmegenThe Netherlands
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14
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Understanding chemical reactivity using the activation strain model. Nat Protoc 2020; 15:649-667. [PMID: 31925400 DOI: 10.1038/s41596-019-0265-0] [Citation(s) in RCA: 160] [Impact Index Per Article: 40.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2019] [Accepted: 10/29/2019] [Indexed: 12/20/2022]
Abstract
Understanding chemical reactivity through the use of state-of-the-art computational techniques enables chemists to both predict reactivity and rationally design novel reactions. This protocol aims to provide chemists with the tools to implement a powerful and robust method for analyzing and understanding any chemical reaction using PyFrag 2019. The approach is based on the so-called activation strain model (ASM) of reactivity, which relates the relative energy of a molecular system to the sum of the energies required to distort the reactants into the geometries required to react plus the strength of their mutual interactions. Other available methods analyze only a stationary point on the potential energy surface, but our methodology analyzes the change in energy along a reaction coordinate. The use of this methodology has been proven to be critical to the understanding of reactions, spanning the realms of the inorganic and organic, as well as the supramolecular and biochemical, fields. This protocol provides step-by-step instructions-starting from the optimization of the stationary points and extending through calculation of the potential energy surface and analysis of the trend-decisive energy terms-that can serve as a guide for carrying out the analysis of any given reaction of interest within hours to days, depending on the size of the molecular system.
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15
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Savoo N, Laloo JZA, Rhyman L, Ramasami P, Bickelhaupt FM, Poater J. Activation Strain Analyses of Counterion and Solvent Effects on the Ion-Pair S N 2 Reaction of NH 2 - and CH 3 Cl. J Comput Chem 2019; 41:317-327. [PMID: 31713259 DOI: 10.1002/jcc.26104] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Revised: 10/21/2019] [Accepted: 10/21/2019] [Indexed: 11/09/2022]
Abstract
We have computationally studied the bimolecular nucleophilic substitution (SN 2) reactions of Mn NH2 (n-1) + CH3 Cl (M+ = Li+ , Na+ , K+ , and MgCl+ ; n = 0, 1) in the gas phase and in tetrahydrofuran solution at OLYP/6-31++G(d,p) using polarizable continuum model implicit solvation. We wish to explore and understand the effect of the metal counterion M+ and of solvation on the reaction profile and the stereochemical preference, that is, backside (SN 2-b) versus frontside attack (SN 2-f). The results were compared to the corresponding ion-pair SN 2 reactions involving F- and OH- nucleophiles. Our analyses with an extended activation strain model of chemical reactivity uncover and explain various trends in SN 2 reactivity along the nucleophiles F- , OH- , and NH 2 - , including solvent and counterion effects. © 2019 Wiley Periodicals, Inc.
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Affiliation(s)
- Nandini Savoo
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit, 80837, Mauritius
| | - Jalal Z A Laloo
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit, 80837, Mauritius
| | - Lydia Rhyman
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit, 80837, Mauritius.,Department of Chemical Sciences, University of Johannesburg, Doornfontein Campus, Johannesburg, 2028, South Africa
| | - Ponnadurai Ramasami
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit, 80837, Mauritius.,Department of Chemical Sciences, University of Johannesburg, Doornfontein Campus, Johannesburg, 2028, South Africa
| | - F Matthias Bickelhaupt
- Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, NL-1081 HV, Amsterdam, The Netherlands.,Institute for Molecules and Materials, Radboud University Nijmegen, NL-6525 AJ, Nijmegen, The Netherlands
| | - Jordi Poater
- Departament de Química Inorgànica i Orgànica & IQTCUB, Universitat de Barcelona, 08028, Barcelona, Spain.,ICREA, 08010, Barcelona, Spain
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16
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Boughlala Z, Fonseca Guerra C, Bickelhaupt FM. Alkali Metal Cation Affinities of Neutral Maingroup-Element Hydrides across the Periodic Table. J Phys Chem A 2019; 123:9137-9148. [PMID: 31294982 PMCID: PMC6816011 DOI: 10.1021/acs.jpca.9b03814] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
![]()
We have carried out
an extensive quantum chemical exploration of
gas-phase alkali metal cation affinities (AMCAs) of archetypal neutral
bases across the periodic system using relativistic density functional
theory. One objective of this work is to provide an intrinsically
consistent set of values of the 298 K AMCAs of all neutral maingroup-element
hydrides XHn of groups 15–18 along
the periods 1–6. Our main purpose is to understand these trends
in terms of the underlying bonding mechanism using Kohn–Sham
molecular orbital theory together with a canonical energy decomposition
analysis (EDA). We compare the trends in XHn AMCAs with the trends in XHn proton
affinities (PAs). We also examine the differences between the trends
in AMCAs of the neutral XHn bases with
those in the corresponding anionic XHn–1– bases. Furthermore, we analyze how the cation
affinity of our neutral Lewis bases changes along the group-1 cations
H+, Li+, Na+, K+, Rb+, and Cs+.
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Affiliation(s)
- Zakaria Boughlala
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM) , Vrije Universiteit Amsterdam , De Boelelaan 1083 , NL-1081 HV Amsterdam , The Netherlands
| | - Célia Fonseca Guerra
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM) , Vrije Universiteit Amsterdam , De Boelelaan 1083 , NL-1081 HV Amsterdam , The Netherlands.,Leiden Institute of Chemistry , Leiden University , PO Box 9502, NL-2300 RA Leiden , The Netherlands
| | - F Matthias Bickelhaupt
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM) , Vrije Universiteit Amsterdam , De Boelelaan 1083 , NL-1081 HV Amsterdam , The Netherlands.,Institute of Molecules and Materials , Radboud University , Heyendaalseweg 135 , NL-6525 AJ Nijmegen , The Netherlands
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17
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Effect of solvent polarity on the potential energy surface in the SN2 reaction of F− + CH3Cl. COMPUT THEOR CHEM 2019. [DOI: 10.1016/j.comptc.2019.01.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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18
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Larrañaga O, de Cózar A. Effect of an α-Methyl Substituent on the Dienophile on Diels-Alder endo: exo Selectivity. ChemistryOpen 2019; 8:49-57. [PMID: 30652065 PMCID: PMC6333242 DOI: 10.1002/open.201800237] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2018] [Revised: 11/23/2018] [Indexed: 11/29/2022] Open
Abstract
A detailed computational study of the Diels‐Alder reaction of cyclopentadiene with acrylonitrile, methylacrylate and their α‐methylated counterparts methacrylonitrile and methyl methacrylate at the M06‐2X(PCM)/TZVP level of theory has been performed. We want to understand the excellent exo‐selectivities observed experimentally due the presence of this substituent. To this end, analysis of the reaction coordinate by means of activation strain model of chemical reactivity (ASM‐distortion interaction model) including solvation effects and NBO second order perturbation energy have been carried out.
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Affiliation(s)
- Olatz Larrañaga
- Departamento de Química Orgánica I Facultad de Química Universidad del País Vasco and Donostia International Physics Center (DIPC) P. K. 1072 E-20018 San Sebastián-Donostia Spain
| | - Abel de Cózar
- Departamento de Química Orgánica I Facultad de Química Universidad del País Vasco and Donostia International Physics Center (DIPC) P. K. 1072 E-20018 San Sebastián-Donostia Spain.,IKERBASQUE Basque Foundation for Science E-48013 Bilbao Spain
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19
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Laloo JZA, Savoo N, Laloo N, Rhyman L, Ramasami P. ExcelAutomat 1.3: Fragment analysis based on the distortion/interaction-activation strain model. J Comput Chem 2018; 40:619-624. [DOI: 10.1002/jcc.25546] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2018] [Revised: 06/27/2018] [Accepted: 07/07/2018] [Indexed: 12/15/2022]
Affiliation(s)
- Jalal Z. A. Laloo
- Computational Chemistry Group, Department of Chemistry, Faculty of Science; University of Mauritius; Réduit 80837 Mauritius
| | - Nandini Savoo
- Computational Chemistry Group, Department of Chemistry, Faculty of Science; University of Mauritius; Réduit 80837 Mauritius
| | - Nassirah Laloo
- School of Innovative Technologies and Engineering, Department of Creative Arts, Film and Media Technologies, University of Technology; Mauritius, La Tour Koenig, Pointe-aux-Sables 11129 Mauritius
| | - Lydia Rhyman
- Computational Chemistry Group, Department of Chemistry, Faculty of Science; University of Mauritius; Réduit 80837 Mauritius
- Department of Applied Chemistry; University of Johannesburg, Doornfontein Campus; Johannesburg 2028 South Africa
| | - Ponnadurai Ramasami
- Computational Chemistry Group, Department of Chemistry, Faculty of Science; University of Mauritius; Réduit 80837 Mauritius
- Department of Applied Chemistry; University of Johannesburg, Doornfontein Campus; Johannesburg 2028 South Africa
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20
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Satpathy L, Sahu PK, Behera PK, Mishra BK. Solvent Effect on the Potential Energy Surfaces of the F - + CH 3CH 2Br Reaction. J Phys Chem A 2018; 122:5861-5869. [PMID: 29909618 DOI: 10.1021/acs.jpca.8b02687] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Although substantial work has been undertaken on reaction pathways involved in base-promoted elimination reactions and bimolecular nucleophilic substitution reaction of F- on CH3CH2X (X = Cl, Br, I), the effect of solvents with varying dielectric constants on the stereochemistry of each of the reaction species involved across the reaction profile have not yet been clearly understood. The present investigation reports the effect of solvents on the potential energy surfaces (PES) and structures of the species appearing in the reaction pathway of F- with bromoethane. The PESs in the gas phase have been computed at MP2 level and CCSD(T) level. The performance of several hybrid density functional, such as B3LYP, M06, M06L, BHandH, X3LYP, M05, M05-2X, and M06-2X have also been investigated toward describing the elimination and nucleophilic substitution reactions. With respect to MAE values and to make the computation cost-effective, we have explored the implicit continuum solvent model, CPCM in solvents like cyclohexane, methanol, acetonitrile, dimethyl sulfoxide and water. The reactant complexes proceed through the subsequent steps to produce fluoroethane as the substitution product and ethylene as one of the elimination products. For elimination reaction both syn and anti elimination have been explored. The calculated relatives energies values, which are negative in the gas phase, are found to be positive in polar solvents since the point charge in the separated reactants are more stabilized than the dispersed charge in the transient complex, which has also been analyzed through NBO analysis.
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Affiliation(s)
- Lopamudra Satpathy
- Centre of Studies in Surface Science and Technology, School of Chemistry , Sambalpur University , Jyoti Vihar 768 019 , India
| | - Prabhat K Sahu
- Computational Modeling Research Laboratory , School of Chemistry Sambalpur University , Jyoti Vihar 768 019 , India
| | - Pradipta K Behera
- Centre of Studies in Surface Science and Technology, School of Chemistry , Sambalpur University , Jyoti Vihar 768 019 , India
| | - Bijay K Mishra
- Centre of Studies in Surface Science and Technology, School of Chemistry , Sambalpur University , Jyoti Vihar 768 019 , India
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21
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Hamlin TA, Swart M, Bickelhaupt FM. Nucleophilic Substitution (S N 2): Dependence on Nucleophile, Leaving Group, Central Atom, Substituents, and Solvent. Chemphyschem 2018; 19:1315-1330. [PMID: 29542853 PMCID: PMC6001448 DOI: 10.1002/cphc.201701363] [Citation(s) in RCA: 118] [Impact Index Per Article: 19.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Indexed: 11/12/2022]
Abstract
The reaction potential energy surface (PES), and thus the mechanism of bimolecular nucleophilic substitution (SN 2), depends profoundly on the nature of the nucleophile and leaving group, but also on the central, electrophilic atom, its substituents, as well as on the medium in which the reaction takes place. Here, we provide an overview of recent studies and demonstrate how changes in any one of the aforementioned factors affect the SN 2 mechanism. One of the most striking effects is the transition from a double-well to a single-well PES when the central atom is changed from a second-period (e. g. carbon) to a higher-period element (e.g, silicon, germanium). Variations in nucleophilicity, leaving group ability, and bulky substituents around a second-row element central atom can then be exploited to change the single-well PES back into a double-well. Reversely, these variations can also be used to produce a single-well PES for second-period elements, for example, a stable pentavalent carbon species.
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Affiliation(s)
- Trevor A. Hamlin
- Department of Theoretical Chemistry andAmsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081 HVAmsterdamThe Netherlands
| | - Marcel Swart
- Department of Theoretical Chemistry andAmsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081 HVAmsterdamThe Netherlands
- Institut de Química Computacional I Catàlisi and Department de QuímicaUniversitat de Girona17003GironaSpain
- ICREAPg. Lluís Companys 2308010BarcelonaSpain
| | - F. Matthias Bickelhaupt
- Department of Theoretical Chemistry andAmsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081 HVAmsterdamThe Netherlands
- Institute of Molecules and Materials (IMM)Radboud UniversityHeyendaalseweg 1356525 AJNijmegenThe Netherlands
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22
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Hamlin TA, van Beek B, Wolters LP, Bickelhaupt FM. Nucleophilic Substitution in Solution: Activation Strain Analysis of Weak and Strong Solvent Effects. Chemistry 2018; 24:5927-5938. [PMID: 29457865 PMCID: PMC5947303 DOI: 10.1002/chem.201706075] [Citation(s) in RCA: 42] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Indexed: 12/23/2022]
Abstract
We have quantum chemically studied the effect of various polar and apolar solvents on the shape of the potential energy surface (PES) of a diverse collection of archetypal nucleophilic substitution reactions at carbon, silicon, phosphorus, and arsenic by using density functional theory at the OLYP/TZ2P level. In the gas phase, all our model SN 2 reactions have single-well PESs, except for the nucleophilic substitution reaction at carbon (SN 2@C), which has a double-well energy profile. The presence of the solvent can have a significant effect on the shape of the PES and, thus, on the nature of the SN 2 process. Solvation energies, charges on the nucleophile or leaving group, and structural features are compared for the various SN 2 reactions in a spectrum of solvents. We demonstrate how solvation can change the shape of the PES, depending not only on the polarity of the solvent, but also on how the charge is distributed over the interacting molecular moieties during different stages of the reaction. In the case of a nucleophilic substitution at three-coordinate phosphorus, the reaction can be made to proceed through a single-well [no transition state (TS)], bimodal barrier (two TSs), and then through a unimodal transition state (one TS) simply by increasing the polarity of the solvent.
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Affiliation(s)
- Trevor A. Hamlin
- Department of Theoretical ChemistryAmsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081 HVAmsterdamThe Netherlands
| | - Bas van Beek
- Department of Theoretical ChemistryAmsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081 HVAmsterdamThe Netherlands
| | - Lando P. Wolters
- Department of Theoretical ChemistryAmsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081 HVAmsterdamThe Netherlands
| | - F. Matthias Bickelhaupt
- Department of Theoretical ChemistryAmsterdam Center for Multiscale Modeling (ACMM)Vrije Universiteit AmsterdamDe Boelelaan 10831081 HVAmsterdamThe Netherlands
- Institute of Molecules and Materials (IMM)Radboud University NijmegenHeyendaalseweg 1356525 AJNijmegenThe Netherlands
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23
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van Bochove MA, Roos G, Fonseca Guerra C, Hamlin TA, Bickelhaupt FM. How Mg 2+ ions lower the S N2@P barrier in enzymatic triphosphate hydrolysis. Chem Commun (Camb) 2018. [PMID: 29537051 DOI: 10.1039/c8cc00700d] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Our quantum chemical activation strain analyses demonstrate how Mg2+ lowers the barrier of the enzymatic triphosphate hydrolysis through two distinct mechanisms: (a) weakening of the leaving-group bond, thereby decreasing activation strain; and (b) transition state (TS) stabilization through enhanced electrophilicity of the triphosphate PPP substrate, thereby strengthening the interaction with the nucleophile.
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Affiliation(s)
- Marc A van Bochove
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling, Vrije Universiteit Amsterdam, De Boelelaan 1083, NL-1081 HV Amsterdam, The Netherlands.
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24
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Laloo JZA, Rhyman L, Larrañaga O, Ramasami P, Bickelhaupt FM, de Cózar A. Ion-Pair S N 2 Reaction of OH - and CH 3 Cl: Activation Strain Analyses of Counterion and Solvent Effects. Chem Asian J 2018; 13:1138-1147. [PMID: 29437289 DOI: 10.1002/asia.201800082] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Revised: 02/12/2018] [Indexed: 11/10/2022]
Abstract
We have theoretically studied the non-identity SN 2 reactions of Mn OH(n-1) +CH3 Cl (M+ =Li+ , Na+ , K+ , and MgCl+ ; n=0, 1) in the gas phase and in THF solution at the OLYP/6-31++G(d,p) level using polarizable continuum model (PCM) implicit solvation. We want to explore and understand the effect of the metal counterion M+ and solvation on the reaction profile and the stereoselectivity of these processes. To this end, we have explored the potential energy surfaces of the backside (SN 2-b) and frontside (SN 2-f) pathways. To explain the computed trends, we have carried out analyses with an extended activation strain model (ASM) of chemical reactivity that includes the treatment of solvation effects.
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Affiliation(s)
- Jalal Z A Laloo
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit, 80837, Mauritius
| | - Lydia Rhyman
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit, 80837, Mauritius.,Department of Applied Chemistry, University of Johannesburg, Doornfontein Campus, Johannesburg, 2028, South Africa
| | - Olatz Larrañaga
- Departamento de Química Orgánica I, Facultad de Química, Universidad del País Vasco (UPV/EHU) and Donostia International Physics Center (DIPC), P. K. 1072, 20018, San Sebastián-Donostia, Spain
| | - Ponnadurai Ramasami
- Computational Chemistry Group, Department of Chemistry, Faculty of Science, University of Mauritius, Réduit, 80837, Mauritius.,Department of Applied Chemistry, University of Johannesburg, Doornfontein Campus, Johannesburg, 2028, South Africa
| | - F Matthias Bickelhaupt
- Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081, HV, Amsterdam, The Netherlands.,Institute of Molecules and Materials, Radboud University, Heyendaalseweg 135, 6525, AJ, Nijmegen, The Netherlands
| | - Abel de Cózar
- Departamento de Química Orgánica I, Facultad de Química, Universidad del País Vasco (UPV/EHU) and Donostia International Physics Center (DIPC), P. K. 1072, 20018, San Sebastián-Donostia, Spain.,Department of Theoretical Chemistry, Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081, HV, Amsterdam, The Netherlands.,IKERBASQUE, Basque Foundation for Science, 48013, Bilbao, Spain
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25
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Levandowski BJ, Hamlin TA, Helgeson RC, Bickelhaupt FM, Houk KN. Origins of the Endo and Exo Selectivities in Cyclopropenone, Iminocyclopropene, and Triafulvene Diels-Alder Cycloadditions. J Org Chem 2018; 83:3164-3170. [PMID: 29470085 PMCID: PMC6314817 DOI: 10.1021/acs.joc.8b00025] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The endo and exo stereoselectivities of Diels-Alder reactions of cyclopropenone, iminocyclopropene, and substituted triafulvenes with butadiene were rationalized using density functional theory calculations. When cyclopropenone is the dienophile, there is a 1.8 kcal/mol preference for the exo cycloaddition with butadiene, while the reaction of 3-difluoromethylene triafulvene with butadiene favors the endo cycloaddition by 2.8 kcal/mol. The influence of charge transfer and secondary orbital interactions on the stereoselectivity of Diels-Alder reactions involving triafulvenes and heteroanalogs is discussed. The predicted stereoselectivity correlates with both the charge and highest occupied molecular orbital (HOMO) coefficient at the C3 carbon of the triafulvene motif.
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Affiliation(s)
- Brian J Levandowski
- Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095 , United States
| | - Trevor A Hamlin
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM) , Vrije Universiteit Amsterdam , 1081 HV Amsterdam , The Netherlands
| | - Roger C Helgeson
- Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095 , United States
| | - F Matthias Bickelhaupt
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM) , Vrije Universiteit Amsterdam , 1081 HV Amsterdam , The Netherlands
- Institute for Molecules and Materials (IMM) , Radboud University , 6525 AJ Nijmegen , The Netherlands
| | - K N Houk
- Department of Chemistry and Biochemistry , University of California , Los Angeles , California 90095 , United States
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26
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Boughlala Z, Fonseca Guerra C, Bickelhaupt FM. Alkali Metal Cation Affinities of Anionic Main Group-Element Hydrides Across the Periodic Table. Chem Asian J 2017; 12:2604-2611. [DOI: 10.1002/asia.201700956] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2017] [Indexed: 11/10/2022]
Affiliation(s)
- Zakaria Boughlala
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM); Vrije Universiteit Amsterdam; De Boelelaan 1083 1081 HV Amsterdam NL
| | - Célia Fonseca Guerra
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM); Vrije Universiteit Amsterdam; De Boelelaan 1083 1081 HV Amsterdam NL
- Leiden Institute of Chemistry; Leiden University; PO Box 9502 2300 RA Leiden NL
| | - F. Matthias Bickelhaupt
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM); Vrije Universiteit Amsterdam; De Boelelaan 1083 1081 HV Amsterdam NL
- Institute of Molecules and Materials; Radboud University; Heyendaalseweg 135 6525 AJ Nijmegen NL
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27
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Bickelhaupt FM, Houk KN. Das Distortion/Interaction‐Activation‐Strain‐Modell zur Analyse von Reaktionsgeschwindigkeiten. Angew Chem Int Ed Engl 2017. [DOI: 10.1002/ange.201701486] [Citation(s) in RCA: 176] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- F. Matthias Bickelhaupt
- Department of Theoretical Chemistry und Amsterdam Center for Multiscale Modeling (ACMM) Vrije Universiteit Amsterdam De Boelelaan 1083 1081 HV Amsterdam Niederlande
- Institute of Molecules and Materials (IMM) Radboud University Heyendaalseweg 135 6525 AJ Nijmegen Niederlande
| | - Kendall N. Houk
- Department of Chemistry and Biochemistry und Department of Chemical and Biomolecular Engineering University of California Los Angeles CA 90095-1569 USA
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28
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Bickelhaupt FM, Houk KN. Analyzing Reaction Rates with the Distortion/Interaction-Activation Strain Model. Angew Chem Int Ed Engl 2017; 56:10070-10086. [PMID: 28447369 PMCID: PMC5601271 DOI: 10.1002/anie.201701486] [Citation(s) in RCA: 938] [Impact Index Per Article: 134.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2017] [Revised: 04/10/2017] [Indexed: 12/21/2022]
Abstract
The activation strain or distortion/interaction model is a tool to analyze activation barriers that determine reaction rates. For bimolecular reactions, the activation energies are the sum of the energies to distort the reactants into geometries they have in transition states plus the interaction energies between the two distorted molecules. The energy required to distort the molecules is called the activation strain or distortion energy. This energy is the principal contributor to the activation barrier. The transition state occurs when this activation strain is overcome by the stabilizing interaction energy. Following the changes in these energies along the reaction coordinate gives insights into the factors controlling reactivity. This model has been applied to reactions of all types in both organic and inorganic chemistry, including substitutions and eliminations, cycloadditions, and several types of organometallic reactions.
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Affiliation(s)
- F Matthias Bickelhaupt
- Department of Theoretical Chemistry and Amsterdam Center for Multiscale Modeling (ACMM), Vrije Universiteit Amsterdam, De Boelelaan 1083, 1081 HV, Amsterdam, The Netherlands.,Institute of Molecules and Materials (IMM), Radboud University, Heyendaalseweg 135, 6525 AJ, Nijmegen, The Netherlands
| | - Kendall N Houk
- Department of Chemistry and Biochemistry and Department of Chemical and Biomolecular Engineering, University of California, Los Angeles, CA, 90095-1569, USA
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