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A pragmatic procedure for predicting regioselectivity in nucleophilic substitution of aromatic fluorides
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).ORCID iD: 0000-0003-2673-075X
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2011 (English)In: Tetrahedron Letters, ISSN 0040-4039, E-ISSN 1359-8562, Vol. 52, 3150-3153 p.Article in journal (Refereed) Published
Abstract [en]

The scope and limitations of a method for predicting the regioisomer distribution in kinetically controlled nucleophilic substitution reactions of aromatic fluorides have been investigated. This method is based on calculating the relative stabilities of the isomeric σ-complex intermediates using DFT. A wide set of substrates and anionic nucleophiles have been investigated. Predictions from this method can be used quantitatively—these agree to an average accuracy of ±0.5 kcal/mol with experimental observations in eleven of the twelve investigated reactions.

Place, publisher, year, edition, pages
Elsevier, 2011. Vol. 52, 3150-3153 p.
Keyword [en]
Nucleophilic substitution; Regioselectivity; Computational; sigma-Complex; DFT
National Category
Physical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-204496DOI: 10.1016/j.tetlet.2011.04.032ISI: 000292350800023Scopus ID: 2-s2.0-79956042668OAI: oai:DiVA.org:kth-204496DiVA: diva2:1084963
Note

Artikeln ingår som ett delarbete i en doktorsavhandling. QC 20170411

Available from: 2017-03-27 Created: 2017-03-27 Last updated: 2017-05-10Bibliographically 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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