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Magnus Thesis 20170507 Utan Spikblad Quantum Chemical Studies of Aromatic Substitution Reactions Magnus Liljenberg KTH Royal Institute of Technology School of Chemical Science and Engineering Department of Chemistry Applied Physical Chemistry SE-100 44 Stockholm, Sweden I ISBN 978-91-7729-324-8 ISSN 1654-1081 TRITA-CHE-Report 2017:11 Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm framlägges till offentlig granskning för avläggande av doktorsexamen i kemivetenskap onsdagen den 7 juni 2017 kl 13:00 i sal F3, KTH, Lindstedtsvägen 26, Stockholm. Avhandlingen försvaras på engelska. Opponent är Leif Eriksson, Göteborgs Universitet. © Magnus Liljenberg, 2017 Universitetsservice US AB, Stockholm II To Ingrid, my beloved wife III Magnus Liljenberg, 2017: ”Quantum Chemical Studies of Aromatic Substitution Reactions”, KTH Chemical Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden. Abstract In this thesis, density functional theory (DFT) is used to investigate the mechanisms and reactivities of electrophilic and nucleophilic aromatic substitution reactions (SEAr and SNAr respectively). For SEAr, the σ-complex intermediate is preceded by one (halogenation) or two (nitration) π-complex intermediates. Whereas the rate-determining transition state (TS) for nitration resembles the second π-complex, the corresponding chlorination TS is much closer to the σ-complex. The last step, the expulsion of the proton, is modeled with an explicit solvent molecule in combination with PCM and confirmed to be a nearly barrierless process for nitration/chlorination and involves a substantial energy barrier for iodination. It is also shown for nitration that the gas phase structures and energetics are very different from those in polar solvent. The potential energy surface for SNAr reactions differs greatly depending on leaving group; the σ-complex intermediate exist for F-/HF, but for Cl-/HCl or Br-/HBr the calculations indicate a concerted mechanism. These mechanistic results form a basis for the investigations of predictive reactivity models for aromatic substitution reactions. For SEAr reactions, the free energy of the rate-determining TS reproduces both local (regioselectivity) and global reactivity (substrate selectivity) with good to excellent accuracy. - - For SNAr reactions good accuracies are obtained for Cl /HCl or Br /HBr as leaving group, using TS structures representing a one-step concerted mechanism. The σ-complex intermediate can be used as a reactivity indicator for the TS energy, and for SEAr the accuracy of this method varies in a way that can be rationalized with the Hammond postulate. It is more accurate the later the rate-determining TS, that is the more deactivated the reaction. For - SNAr reactions with F /HF as leaving group, the same method gives excellent accuracy for both local and global reactivity irrespective of the degree of activation. Keywords: electrophilic aromatic substitution, nucleophilic aromatic substitution, quantum chemistry, mechanism, reactivity, prediction model. IV Sammanfattning på svenska I denna avhandling har beräkningskemiska metoder använts för att undersöka mekanismen och reaktiviteten hos elektrofil och nukleofil aromatisk substitution (SEAr respektive SNAr). För SEAr föregås σ-komplexet av en π- komplexintermediär vid halogeneringar och av två stycken vid nitreringar. Medan det hastighetsbestämmande övergångstillståndet vid nitreringar liknar det andra π-komplexet så är motsvarande kloreringsstruktur mycket mer lik σ-komplexet. Reaktionens sista steg, avspjälkningen av en proton, modellerades med en explicit lösningsmedelsmolekyl tillsammans med en PCM modell, och det bekräftades teoretiskt att för nitrering och halogenering så sker detta i det närmaste utan energibarriär. För jodering så var denna barriär däremot betydande. För nitrering så är såväl gasfasstrukturerna som energiförhållandena mycket olika de i polära lösningsmedel. Vidare skiljer sig potentialenergiytan för SNAr reaktioner kraftigt åt beroende på lämnande grupp, σ-complex intermediären finns med F-/HF, men för Cl-/HCl eller Br- /HBr så indikerar beräkningarna en enstegsreaktion utan intermediärer. Dessa mekanistiska resultat utgör basen då prediktiva reaktivitetsmodeller för aromatisk substitution undersöktes. För SEAr gav den fria energin för det hastighetsbestämmande övergångstillståndet både lokal (regioselektivitet) och global reaktivitet (substratselektivitet) med god till utmärkt noggrannhet. För SNAr erhölls god noggrannhet med Cl¯/HCl och Br¯/HBr som lämnande grupper då sådana övergångsstrukturer som representerar en enstegsreaktion användes. Reaktionsintermediären (σ-komplexet) kan användas som reaktivitetsindikator till energin för det hastighetsbestämmande övergångstillståndet, och för SEAr varierade noggrannheten för denna metod på ett sätt som kan förklaras med hjälp av Hammonds postulat. Denna metod är mer noggrann ju senare det hastighetsbestämmande övergångstillståndet ligger, d v s ju mer deaktiverad reaktionen är. För SNAr med F¯/HF som lämnande grupp erhölls utmärkt noggrannhet för både lokal och global reaktivitet med samma metod, oberoende av reaktionens aktiveringsgrad. V Abbreviations ALIE Average local ionization Energy AM1 Austin Model 1 (a semi-empirical method) B3LYP Becke’s three-parameter exchange functional together with the Lee–Yang–Parr correlation functional CAS Complete active space CC Coupled cluster CCSD(T) Coupled cluster with singles, doubles, and noniterative triples excitations CI Configuration interaction DFA Density functional approximation DFT Density functional theory FMO Frontier molecular orbital GGA Generalized gradient approximation GMP Good manufacturing practice GVB Generalized valence bond HF Hartree-Fock HOMO Highest occupied molecular orbital IRC Intrinsic reaction coordinate IRMPD Infrared multi photon dissociation KIE Kinetic isotope effect KS Kohn–Sham LCAO Linear combination of atomic orbitals LDA Local density approximation LUMO Lowest unoccupied molecular orbital MAD Mean Absolute Deviation M06-2X Minnesota exchange correlation functional published 2006 with double amount of exact exchange MC-SCF Multiconfigurational self-consistent field MEP Minimum energy path MINDO Modified intermediate neglect of differential overlap (a semi- empirical method) MNDO Modified neglect of diatomic overlap (a semi-empirical method) MO Molecular orbital MP2 Second-order Møller–Plesset perturbation theory MR-CI Multireference configuration interaction MM Molecular mechanics PCM Polarizable continuum model PES Potential energy surface VI QM Quantum mechanics SEAr Electrophilic aromatic substitution SNAr Nucleophilic aromatic substitution SET Single-electron transfer TS Transition state VB Valence bond VII List of Publications This thesis is based on the following papers, referred to in the text by their Roman numerals I-VI: I. Validation of a computational model for predicting the site for electrophilic substitution in aromatic systems Magnus Liljenberg, Tore Brinck, Björn Herschend, Tobias Rein, Glen Rockwell and Mats Svensson J. Org. Chem. 2010, 75, 4696-4705 II. A pragmatic procedure for predicting regioselectivity in nucleophilic substitution of aromatic fluorides Magnus Liljenberg, Tore Brinck, Björn Herschend, Tobias Rein, Glen Rockwell and Mats Svensson Tetrahedron Lett. 2011, 52, 3150-3153 III. Predicting regioselectivity in nucleophilic aromatic substitution Magnus Liljenberg, Tore Brinck, Björn Herschend, Tobias Rein, Simone Tomasi and Mats Svensson J. Org. Chem. 2012, 77, 3262-3269 IV. Utilizing the σ-complex stability for quantifying reactivity in nucleophilic substitution of aromatic fluorides Magnus Liljenberg, Tore Brinck, Tobias Rein and Mats Svensson Beilstein J. Org. Chem. 2013, 9, 791-799 V. Theoretical investigation of regioselectivity in electrophilic aromatic nitration Magnus Liljenberg, Joakim Halldin Stenlid and Tore Brinck Manuscript VI. Investigation into rate-determining factors in electrophilic aromatic halogenation Magnus Liljenberg, Joakim Halldin Stenlid and Tore Brinck Manuscript Papers not included in this thesis: I. The use of quantum chemistry for mechanistic analyses of SEAr reactions Tore Brinck and Magnus Liljenberg Arene chemistry: reaction mechanisms and methods for aromatic compounds. Edited by Jacques Mortier, Wiley 2016 (ISBN: 978-1-118-75201-2), chapter 4, 83-105 VIII Author´s contributions Paper (I)-(II). I performed all the calculations and wrote parts of the manuscript. Paper (III)-(IV). I formulated the research problem together with T. Brinck, performed most of the calculations and wrote parts of the manuscript. Paper (V)-(VI). I formulated the research problem, performed most of the calculations and wrote a major part of the manuscript. IX Table of Contents Abstract ......................................................................................................... IV Sammanfattning på svenska ........................................................................... V Abbreviations ................................................................................................ VI List of Publications .................................................................................... VIII Author´s contributions .................................................................................. IX Table of Contents ........................................................................................... X Introduction ....................................................................................................
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