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Predicting Regioselectivity in Nucleophilic Aromatic Substitution
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).ORCID iD: 0000-0003-2673-075X
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2012 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 77, no 7, 3262-3269 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated practical and computationally efficient methods for the quantitative prediction of regioisomer distribution in kinetically controlled nucleophilic aromatic substitution reactions. One of the methods is based on calculating the relative stabilities of the isomeric sigma-complex intermediates using DFT. We show that predictions from this method can be used quantitatively both for anionic nucleophiles with F- as leaving group, as well as for neutral nucleophiles with HF as leaving group. The sigma-complex approach failed when the leaving group was Cl/HCl or Br/HBr, both for anionic and neutral nucleophiles, because of difficulties in finding relevant sigma-complex structures. An approach where we assumed a concerted substitution step and used such transition state structures gave quantitatively useful results. Our results are consistent with other theoretical works, where a stable sigma-complex has been identified in some cases, whereas others have been indicated to proceed via a concerted substitution step.

Place, publisher, year, edition, pages
2012. Vol. 77, no 7, 3262-3269 p.
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-93912DOI: 10.1021/jo202569nISI: 000302388000023Scopus ID: 2-s2.0-84859611539OAI: oai:DiVA.org:kth-93912DiVA: diva2:525140
Note

QC 20120507. Artikeln ingår som ett delarbete i en doktorsavhandling.

Available from: 2012-05-07 Created: 2012-05-03 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Quantum Chemical Studies of Aromatic Substitution Reactions
Open this publication in new window or tab >>Quantum Chemical Studies of Aromatic Substitution Reactions
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Stockholm: Universitetsservice US AB, Stockholm, 2017. 74 p.
Series
TRITA-CHE-Report, ISSN 1654-1081
National Category
Physical Chemistry
Research subject
Theoretical Chemistry and Biology
Identifiers
urn:nbn:se:kth:diva-206964 (URN)978-91-7729-324-8 (ISBN)
Public defence
2017-06-07, Sal F3, Lindstedtsvägen 26, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 20170510

Available from: 2017-05-10 Created: 2017-05-10 Last updated: 2017-05-10Bibliographically approved

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Brinck, Tore

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