Nitrene formation is the first step of the thermal and photochemical decomposition reactions of organic azides

Soto, Juan; Algarra, Manuel; Peláez, Daniel

doi:10.1039/d1cp05785e

Cited by 21 publications

(15 citation statements)

References 74 publications

(112 reference statements)

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“…To this end, we have performed ab initio quantum chemical calculations at the CASSCF and MS-CASPT2 levels, which are one of the most appropriate theoretical approximations to deal with this class of molecules and most importantly this type of reactions. 23 − 26 It will be shown that our work corroborates and explains in detail the assertions and conclusions given by Platz et al, 22 excepting the population of the second excited state of the diazo compound upon irradiation with the 350 nm light. In fact, we will demonstrate that the variation of the reactivity in changing the excitation wavelength is due to the absorption of the intermediate carbene ( EPC ) at 350 nm.…”

Section: Introductionsupporting

confidence: 90%

Photochemistry of 1-Phenyl-1-diazopropane and Its Diazirine Isomer: A CASSCF and MS-CASPT2 Study

Soto

2022

J. Phys. Chem. A

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In this work, we studied the wavelength (520 or 350 nm) dependence of the photochemical decomposition of 1-phenyl-1-diazopropane (PDP) and 1-phenyl-1-propyl diazirine (PED) by means of high-level ab initio quantum chemical calculations (CASSCF and MS-CASPT2) to obtain qualitative and quantitative results. It is found that the photochemistry of PDP is governed by nonradiative deactivation processes that can involve one or two S1/S0 conical intersections (CI1 and CI2) depending on the wavelength of the radiation; CI2 is only accessible at the shortest wavelength. It is demonstrated that the main intermediate of the photochemistry of the titled compounds is 1-ethyl-1-phenyl carbene (EPC). Upon irradiation of PDP with the 520 nm light, the carbene is always generated in its ground state as closed-shell singlet carbene. In contrast, the 350 nm radiation can directly decompose PDP into S1 carbene (open shell) and N2 when the conical intersection CI2 is avoided. Once the carbene is formed in the S1 state, it can experience excited state intramolecular proton transfer along a seam of crossing (ESIPT-SC) of the S1 and S0 states to yield the alkene derivative; that is, the proton transfer reaction takes places on a degenerate potential energy surface where the two electronic states have equal energy. In addition, it is found that EPC absorbs at 350 nm (double excitations); therefore, there is another possible route that can induce as well a slightly different photochemistry in changing the wavelength of the radiation because the shortest wavelength (when it is intense enough) decreases the amount of available EPC or generates a highly vibrationally excited state of the carbene; that is, after 350 nm excitation, the carbene intermediate can deactivate via radiation emission or can decay through a cascade of conical intersections to its first excited state (S1), where ESIPT-SC is operative again.

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Section: Introductionsupporting

confidence: 90%

Photochemistry of 1-Phenyl-1-diazopropane and Its Diazirine Isomer: A CASSCF and MS-CASPT2 Study

Soto

2022

J. Phys. Chem. A

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“…Open shell singlet nitrene 7 cannot be located on the PES at the chosen DFT level and triplet nitrene 7 is 6.2 kcal mol −1 higher in energy than azide 4 , but there is no experimental evidence for its formation, although nitrenes have been experimentally detected in thermal decompositions of organic azides [24] . Note that Peláez and co‐workers reported that the photochemical and thermal decomposition of organic azides is best described through the use of multiconfigurational CASSCF and MS‐CASPT2 electronic structure calculations [25] . Using these methods, the thermal and photochemical decomposition product is an open shell singlet nitrene, which isomerizes in an almost barrierless process to the corresponding imine derivative.…”

Section: Resultsmentioning

confidence: 99%

Glycine Imine—The Elusive α‐Imino Acid Intermediate in the Reductive Amination of Glyoxylic Acid

et al. 2023

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Simple unhindered aldimines tend to hydrolyze or oligomerize and are therefore spectroscopically not well characterized. Herein we report the formation and spectroscopic characterization of the simplest imino acid, namely glycine imine, by cryogenic matrix isolation IR and UV/Vis spectroscopy. Glycine imine forms after UV irradiation of 2‐azidoacetic acid by N2 extrusion in anti‐(E,E)‐ and anti‐(Z,Z)‐conformation that can be photochemically interconverted. In matrix isolation pyrolysis experiments with 2‐azidoacetic acid, glycine imine cannot be trapped as it further decarboxylates to aminomethylene. In aqueous solution glycine imine is hydrolyzed to hydroxy glycine and hydrated glyoxylic acid. At higher concentrations or in the presence of FeIISO4 as a reducing agent glycine imine undergoes self‐reduction by oxidative decarboxylation chemistry. Glycine imine may be seen as one of the key reaction intermediates connecting prebiotic amino acid and sugar formation chemistry.

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“…[24] Peláez und Mitarbeiter berichteten, dass die photochemische und thermische Zersetzung organischer Azide und deren elektronische Struktur am besten durch die Verwendung von Multikonfigurationsmethoden, wie CAS-SCF und MS-CASPT2, beschrieben wird. [25] Unter Verwendung dieser Methoden ist das thermische und photochemische Zersetzungsprodukt ein offenschaliges Singulett-Nitren, das in einem nahezu barrierefreien Prozess zum entsprechenden Imin-Derivat isomerisiert. Die geschätzte Obergrenze für die Nitren-Imin-Isomerisierung liegt bei weniger als 1 kcal mol À 1 .…”

Section: Ergebnisse Und Diskussionunclassified

Glycinimin – Das schwer fassbare α‐Iminosäure‐Intermediat bei der Reduktiven Aminierung der Glyoxylsäure

et al. 2023

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Einfache ungehinderte Aldimine neigen dazu, zu hydrolysieren oder zu oligomerisieren und sind daher spektroskopisch nicht gut charakterisiert. Wir berichten hier über die Bildung und spektroskopische Charakterisierung der einfachsten Iminosäure, nämlich Glycinimin, mittels kryogener Matrixisolation, IR‐ und UV/Vis‐Spektroskopie. Glycinimin bildet sich nach UV‐Bestrahlung von 2‐Azidoessigsäure durch N2‐Freisetzung in anti‐(E,E)‐ und anti‐(Z,Z)‐Konformationen, die photochemisch ineinander umgewandelt werden können. In Pyrolyseversuchen gekoppelt mit Matrixisolation von 2‐Azidoessigsäure kann Glycinimin nicht isoliert werden, da es weiter zu Aminomethylen decarboxyliert. In wässriger Lösung wird Glycinimin zu Hydroxyglycin und hydratisierter Glyoxylsäure hydrolysiert. Bei höheren Konzentrationen oder in Gegenwart von FeIISO4 als Reduktionsmittel reduziert sich Glycinimin durch oxidative Decarboxylierung selbst. Glycinimin kann als ein Schlüsselintermediat zwischen präbiotischer Aminosäure‐ und Zuckerbildung angesehen werden.

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Nitrene formation is the first step of the thermal and photochemical decomposition reactions of organic azides

Abstract: In this work, the decomposition of a prototypical azide, isopropyl azide, both in the ground and excited states, has been investigated through the use of multiconfigurational CASSCF and MS-CASPT2 electronic...

Cited by 21 publications

References 74 publications

Photochemistry of 1-Phenyl-1-diazopropane and Its Diazirine Isomer: A CASSCF and MS-CASPT2 Study

Photochemistry of 1-Phenyl-1-diazopropane and Its Diazirine Isomer: A CASSCF and MS-CASPT2 Study

Glycine Imine—The Elusive α‐Imino Acid Intermediate in the Reductive Amination of Glyoxylic Acid

Glycinimin – Das schwer fassbare α‐Iminosäure‐Intermediat bei der Reduktiven Aminierung der Glyoxylsäure

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