Theoretical study of non-Hammett vs. Hammett behaviour in the thermolysis and photolysis of arylchlorodiazirines
dc.contributor.author
dc.date.accessioned
2019-05-06T11:28:46Z
dc.date.available
2019-05-06T11:28:46Z
dc.date.issued
2018-01-14
dc.identifier.issn
1463-9076
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dc.description.abstract
Arylchlorodiazirines (ACDA) are thermal and photochemical precursors of carbenes that form these molecules via nitrogen elimination. We have studied this reaction with multireference quantum chemical methods (CASSCF and CASPT2) for a series of ACDA derivatives with different substitution at the aromatic ring. The calculations explain the different reactivity trends found in the ground and excited state, with good correlation between the calculated barriers and the experimental reaction rates. The ground state mechanism can be described as a reverse cycloaddition with small charge transfer from the aromatic ring to the diazirine moiety. This is consistent with the lack of correlation between the Hammett a descriptors and the experimental rates. In contrast, the excited state reaction is the cleavage of a single C-N bond mediated by small barriers of 4-6 kcal mol(-1). The reaction path goes through a conical intersection with the ground state, which facilitates radiationless decay and explains the disappearance of the transient absorption signal measured experimentally. This leads to a diazomethane intermediate that ultimately yields the carbene. Electronically, excitation to S-1 is characterized initially by significant charge transfer from the phenyl ring to the diazirine. The charge transfer is reversed during the C-N cleavage reaction, and this explains the preferential stabilization of the excited-state minimum by polar solvents and electron-donating substituents. Therefore, our calculations reproduce and explain the relationship found experimentally between the Hammett sigma(+) parameters and the life time of S1 (Y. L. Zhang, et al. J. Am. Chem. Soc, 2009, 131, 16652-16653)
dc.description.sponsorship
We acknowledge financial support from the National Natural Science Foundation of China (grants 21773007 and 21303007 for QL); the Spanish Ministerio de Economía y Competitividad (Grants RYC-2011-09582 for AM and CTQ-2015-69363-P for LB); and the Departament d’Innovació, Universitats i Empresa (DIUE), Generalitat de Catalunya (Xarxa de Refere`ncia en Quı´mica Teo`rica i Computacional)
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8 p.
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application/pdf
dc.language.iso
eng
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Royal Society of Chemistry (RSC)
dc.relation
info:eu-repo/grantAgreement/MINECO//CTQ2015-69363-P/ES/OMPUTACION DEL ESTADO EXCITADO: DE ESPECTROS MOLECULARES A SISTEMAS MULTICROMOFORICOS/
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Reproducció digital del document publicat a: https://doi.org/10.1039/c7cp07281c
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Physical Chemistry Chemical Physics, 2018, vol. 20, núm. 2, p. 1181-1188
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Articles publicats (D-Q)
dc.rights
Reconeixement-NoComercial 4.0 Internacional
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dc.source
Peng, Xing-Liang Migani, Annapaola Li, Quansong Li, Ze-Sheng Blancafort San José, Lluís 2018 Theoretical study of non-Hammett vs. Hammett behaviour in the thermolysis and photolysis of arylchlorodiazirines Physical Chemistry Chemical Physics 20 2 1181 1188
dc.subject
dc.title
Theoretical study of non-Hammett vs. Hammett behaviour in the thermolysis and photolysis of arylchlorodiazirines
dc.type
info:eu-repo/semantics/article
dc.rights.accessRights
info:eu-repo/semantics/openAccess
dc.type.version
info:eu-repo/semantics/publishedVersion
dc.identifier.doi
dc.identifier.idgrec
029049
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dc.type.peerreviewed
peer-reviewed
dc.relation.ProjectAcronym
dc.identifier.eissn
1463-9084