Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Validation of a Computational Model for Predicting the Site for Electrophilic Substitution in Aromatic Systems
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Physical Chemistry (closed 20110630).ORCID iD: 0000-0003-2673-075X
Show others and affiliations
2010 (English)In: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 75, no 14, 4696-4705 p.Article in journal (Refereed) Published
Abstract [en]

We have investigated the scope and limitations of a method for predicting the regioisomer distribution in electrophilic aromatic substitution reactions that are under kinetic control. This method is based on calculation of the relative stabilities of the sigma-complex intermediates using density functional theory. Predictions from this method can be used quantitatively for halogenations; it agreed to an accuracy of about 1 kcal/mol with experimental observations in 10 of the 11 investigated halogenation reactions. For nitrations, the method gave useful predictions for heterocyclic substrates. The method failed for nitration of monosubstituted benzenes, and we expect that more elaborate model systems, including explicit solvent molecules, will be necessary to obtain quantitatively useful predictions for such cases. For Lewis acid promoted Friedel Crafts acylations, the method can be expected to give qualitatively correct predictions, that is, to point out the dominating isomer. For substrates where the regioisomeric outcome is highly dependent on the reaction conditions, the method can only be of qualitative use if the concentration of the free Lewis acid is high during the reaction. We have also compared the predictive capacity of the method to that of a modern reactivity index, the average local ionization energy, I(r). The latter method is found to predict the regisolectivity in halogenations and nitrations qualitatively correctly if the positions for the I(r) minima (I-S,I-min) are not too sterically hindered but fails for qualitative predictions of F C reactions. The downscaled I-S,I-min values also perform well for the quantitative prediction of regioisomer distributions of halogenations. The accuracy is slightly lower than that for the new method.

Place, publisher, year, edition, pages
2010. Vol. 75, no 14, 4696-4705 p.
Keyword [en]
FRIEDEL-CRAFTS ACYLATION, LOCAL IONIZATION ENERGIES, NITROGEN-HETEROCYCLES, CONJUGATED MOLECULES, STABLE CARBOCATIONS, RATE CONSTANTS, GROUND-STATES, NITRATION, BENZENE, MECHANISM
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-29508DOI: 10.1021/jo100310vISI: 000279569500004Scopus ID: 2-s2.0-77954549902OAI: oai:DiVA.org:kth-29508DiVA: diva2:394451
Note

QC 20110202. Detta är ett delarbete i en doktorsavhandling.

Available from: 2011-02-02 Created: 2011-02-02 Last updated: 2017-12-11Bibliographically 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

Open Access in DiVA

No full text

Other links

Publisher's full textScopus

Authority records BETA

Brinck, Tore

Search in DiVA

By author/editor
Liljenberg, MagnusBrinck, ToreRein, Tobias
By organisation
Physical Chemistry (closed 20110630)
In the same journal
Journal of Organic Chemistry
Chemical Sciences

Search outside of DiVA

GoogleGoogle Scholar

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 62 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf