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Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C[combining umlaut]–OH)
We report the gas-phase preparation of cyanohydroxycarbene by high-vacuum flash pyrolysis of ethyl 2-cyano-2-oxoacetate and subsequent trapping of the pyrolysate in an inert argon matrix at 3 K. After irradiation of the matrix with green light for a few seconds singlet trans-cyanohydroxycarbene rear...
Autores principales: | , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
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Royal Society of Chemistry
2018
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6345350/ https://www.ncbi.nlm.nih.gov/pubmed/30774874 http://dx.doi.org/10.1039/c8sc03720e |
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author | Eckhardt, André K. Erb, Frederik R. Schreiner, Peter R. |
author_facet | Eckhardt, André K. Erb, Frederik R. Schreiner, Peter R. |
author_sort | Eckhardt, André K. |
collection | PubMed |
description | We report the gas-phase preparation of cyanohydroxycarbene by high-vacuum flash pyrolysis of ethyl 2-cyano-2-oxoacetate and subsequent trapping of the pyrolysate in an inert argon matrix at 3 K. After irradiation of the matrix with green light for a few seconds singlet trans-cyanohydroxycarbene rearranges to its cis-conformer. Prolonged irradiation leads to the formation of cyanoformaldehyde and isomeric isocyanoformaldehyde. Cis- and trans-cyanohydroxycarbene were characterized by matching matrix IR and UV/Vis spectroscopic data with ab initio coupled cluster and TD-DFT computations. Trans-cyanohydroxycarbene undergoes a conformer-specific [1,2]H-tunnelling reaction through a 33.3 kcal mol(–1) barrier (the highest penetrated barrier of all H-tunnelling reactions observed to date) to cyanoformaldehyde with a half-life of 23.5 ± 0.5 d; this is the longest half-life reported for an H-tunnelling process to date. During the tunnelling reaction the cis-conformer remains unchanged over the same period of time and the Curtin–Hammett principle does not apply. NIR irradiation of the O–H stretching overtone does not enhance the tunnelling rate via vibrational activation. Push–pull stabilisation of hydroxycarbenes through σ- and π-withdrawing groups therefore is even more stabilizing than push–push substitution. |
format | Online Article Text |
id | pubmed-6345350 |
institution | National Center for Biotechnology Information |
language | English |
publishDate | 2018 |
publisher | Royal Society of Chemistry |
record_format | MEDLINE/PubMed |
spelling | pubmed-63453502019-02-15 Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C[combining umlaut]–OH) Eckhardt, André K. Erb, Frederik R. Schreiner, Peter R. Chem Sci Chemistry We report the gas-phase preparation of cyanohydroxycarbene by high-vacuum flash pyrolysis of ethyl 2-cyano-2-oxoacetate and subsequent trapping of the pyrolysate in an inert argon matrix at 3 K. After irradiation of the matrix with green light for a few seconds singlet trans-cyanohydroxycarbene rearranges to its cis-conformer. Prolonged irradiation leads to the formation of cyanoformaldehyde and isomeric isocyanoformaldehyde. Cis- and trans-cyanohydroxycarbene were characterized by matching matrix IR and UV/Vis spectroscopic data with ab initio coupled cluster and TD-DFT computations. Trans-cyanohydroxycarbene undergoes a conformer-specific [1,2]H-tunnelling reaction through a 33.3 kcal mol(–1) barrier (the highest penetrated barrier of all H-tunnelling reactions observed to date) to cyanoformaldehyde with a half-life of 23.5 ± 0.5 d; this is the longest half-life reported for an H-tunnelling process to date. During the tunnelling reaction the cis-conformer remains unchanged over the same period of time and the Curtin–Hammett principle does not apply. NIR irradiation of the O–H stretching overtone does not enhance the tunnelling rate via vibrational activation. Push–pull stabilisation of hydroxycarbenes through σ- and π-withdrawing groups therefore is even more stabilizing than push–push substitution. Royal Society of Chemistry 2018-10-31 /pmc/articles/PMC6345350/ /pubmed/30774874 http://dx.doi.org/10.1039/c8sc03720e Text en This journal is © The Royal Society of Chemistry 2019 http://creativecommons.org/licenses/by-nc/3.0/ This article is freely available. This article is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported Licence (CC BY-NC 3.0) |
spellingShingle | Chemistry Eckhardt, André K. Erb, Frederik R. Schreiner, Peter R. Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C[combining umlaut]–OH) |
title | Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C[combining umlaut]–OH)
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title_full | Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C[combining umlaut]–OH)
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title_fullStr | Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C[combining umlaut]–OH)
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title_full_unstemmed | Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C[combining umlaut]–OH)
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title_short | Conformer-specific [1,2]H-tunnelling in captodatively-stabilized cyanohydroxycarbene (NC–C[combining umlaut]–OH)
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title_sort | conformer-specific [1,2]h-tunnelling in captodatively-stabilized cyanohydroxycarbene (nc–c[combining umlaut]–oh) |
topic | Chemistry |
url | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6345350/ https://www.ncbi.nlm.nih.gov/pubmed/30774874 http://dx.doi.org/10.1039/c8sc03720e |
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