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Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine
Benzene imine (1) ⇌ 1H-azepine (2) isomerization occurs through sequential valence and endo–exo isomerism. Quantum chemical and quasiclassical trajectory (QCT) simulations reveal the coupled reaction pathway – ring-expansion followed by N-inversion to the most stable isomer, exo-1H-azepine (Exo-2)....
Autores principales: | , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
The Royal Society of Chemistry
2021
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8769061/ https://www.ncbi.nlm.nih.gov/pubmed/35173935 http://dx.doi.org/10.1039/d1sc04855d |
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author | Mandal, Nilangshu Das, Ankita Hajra, Chandralekha Datta, Ayan |
author_facet | Mandal, Nilangshu Das, Ankita Hajra, Chandralekha Datta, Ayan |
author_sort | Mandal, Nilangshu |
collection | PubMed |
description | Benzene imine (1) ⇌ 1H-azepine (2) isomerization occurs through sequential valence and endo–exo isomerism. Quantum chemical and quasiclassical trajectory (QCT) simulations reveal the coupled reaction pathway – ring-expansion followed by N-inversion to the most stable isomer, exo-1H-azepine (Exo-2). Direct-dynamics produce a mixture of endo- and exo-1H-azepine stereoisomers and govern the endo-1H-azepine (Endo-2) ⇌ exo-1H-azepine (Exo-2) ratio. Exo-2 is computationally identified as the most stable product while Endo-2 is fleetingly stable with a survival time (S(T)) ∼50 fs. N-Methyl substitution exclusively results in an exo-1-methyl-1H-azepine isomer. F-substitution at the N-site increases the barrier for N-inversion and alters the preference by stabilizing Endo-2. Interestingly, the exo-1-fluoro-1H-azepine (minor product) is formed through bifurcation via non-statistical dynamics. A highly concaved Arrhenius plot for 1a → 2a highlights the influence of heavy-atom tunneling on valence isomerism, particularly at low temperatures. Heavy-atom tunneling also results in a normal N–H(D) secondary KIE above 100 K even though the increase in hybridization from sp(2) to sp(3) at nitrogen should cause an inverse KIE classically. |
format | Online Article Text |
id | pubmed-8769061 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2021 |
publisher | The Royal Society of Chemistry |
record_format | MEDLINE/PubMed |
spelling | pubmed-87690612022-02-15 Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine Mandal, Nilangshu Das, Ankita Hajra, Chandralekha Datta, Ayan Chem Sci Chemistry Benzene imine (1) ⇌ 1H-azepine (2) isomerization occurs through sequential valence and endo–exo isomerism. Quantum chemical and quasiclassical trajectory (QCT) simulations reveal the coupled reaction pathway – ring-expansion followed by N-inversion to the most stable isomer, exo-1H-azepine (Exo-2). Direct-dynamics produce a mixture of endo- and exo-1H-azepine stereoisomers and govern the endo-1H-azepine (Endo-2) ⇌ exo-1H-azepine (Exo-2) ratio. Exo-2 is computationally identified as the most stable product while Endo-2 is fleetingly stable with a survival time (S(T)) ∼50 fs. N-Methyl substitution exclusively results in an exo-1-methyl-1H-azepine isomer. F-substitution at the N-site increases the barrier for N-inversion and alters the preference by stabilizing Endo-2. Interestingly, the exo-1-fluoro-1H-azepine (minor product) is formed through bifurcation via non-statistical dynamics. A highly concaved Arrhenius plot for 1a → 2a highlights the influence of heavy-atom tunneling on valence isomerism, particularly at low temperatures. Heavy-atom tunneling also results in a normal N–H(D) secondary KIE above 100 K even though the increase in hybridization from sp(2) to sp(3) at nitrogen should cause an inverse KIE classically. The Royal Society of Chemistry 2021-12-14 /pmc/articles/PMC8769061/ /pubmed/35173935 http://dx.doi.org/10.1039/d1sc04855d Text en This journal is © The Royal Society of Chemistry https://creativecommons.org/licenses/by-nc/3.0/ |
spellingShingle | Chemistry Mandal, Nilangshu Das, Ankita Hajra, Chandralekha Datta, Ayan Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine |
title | Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine |
title_full | Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine |
title_fullStr | Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine |
title_full_unstemmed | Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine |
title_short | Stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine |
title_sort | stereoelectronic and dynamical effects dictate nitrogen inversion during valence isomerism in benzene imine |
topic | Chemistry |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8769061/ https://www.ncbi.nlm.nih.gov/pubmed/35173935 http://dx.doi.org/10.1039/d1sc04855d |
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