Ethynamine - Ketenimine - Acetonitrile - Rearrangements: A computational Study of Flash Vacuum Pyrolysis Processes

Wentrup, Curt; Bégué, Didier; Leung-Toung, Régis

doi:10.26434/chemrxiv.5373964.v1

Cited by 5 publications

(4 citation statements)

References 37 publications

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“…[29] Therefore, such reactions commonly proceed by different, lower-energy mechanisms. [30,31] In our case, the formal 1,3-H shift 3a!5 takes place in the form of two consecutive 1,2-H shifts via the silaazomethine ylide 13 ( Figure 6).…”

Section: Levelsmentioning

confidence: 70%

Trimethylsilylnitrene and Its Surprising Rearrangement to N‐(Dimethylsilyl)methanimine via Silaziridine and Silaazomethine Ylide

Wentrup

Lüerssen

Silva

et al. 2018

Chemistry A European J

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Photolysis of trimethylsilyl azide at 254 nm in Ar matrix at 15 K generates the triplet ground state trimethylsilylnitrene 2 aT, observed by ESR spectroscopy (|D/hc|=1.540 cm ; |E/hc|=0.0002 cm ). Calculations at the CASPT2(14,13) level reveal the open-shell singlet nitrene 2 aS( A") is a discrete intermediate lying ≈38 kcal mol above the triplet. The normally expected rearrangement of the nitrene 2 aS to dimethylsilanimine 3 a has a high calculated barrier (33 kcal mol ), which explains why this product has never been observed. Instead, the singlet nitrene 2 aS inserts into a methyl C-H bond to yield silaziridine 12 via an activation barrier of only 6 kcal mol . Ring opening of 12 generates a 1-silaazomethine ylide 13, in which a facile 1,2-H shift yields N-(dimethylsilyl)methanimine 5, all with barriers well below the energy of the singlet nitrene.

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Section: Levelsmentioning

confidence: 70%

Trimethylsilylnitrene and Its Surprising Rearrangement to N‐(Dimethylsilyl)methanimine via Silaziridine and Silaazomethine Ylide

Wentrup

Lüerssen

Silva

et al. 2018

Chemistry A European J

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“…The ionic isomerization 14 •+ → 15 •+ has a very high calculated barrier of 114 kcal/mol, which makes it uncompetitive in comparison with the other processes considered in Scheme . Similarly high barriers are known for other “forbidden” pericyclic 1,3-H shifts, e.g., the isomerization of ketenimine to acetonitrile . Thus, the three routes to phenylnitrene 8a •+ via the phenylcyanamide 15 •+ , azabicyclo[4.2.0]octadiene 16 •+ , and phenylcarbodiimide 14 •+ ions remain preferred pathways.…”

Section: Resultsmentioning

confidence: 74%

Phenylnitrene Radical Cation and Its Isomers from Tetrazoles, Nitrile Imines, Indazole, and Benzimidazole

et al. 2019

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Phenylnitrene radical cations m/z 91, C 6 H 5 N, 8a •+ are observed in the mass spectra of 1-, 2-, and 5-phenyltetrazoles, even though no C−N bond is present in 5-phenyltetrazole. Calculations at the B3LYP/6-311G(d,p) level of theory indicate that initial formation of the C-phenylimidoylnitrene 13 •+ and/or benzonitrile imine radical cation 19 •+ from 1H-and 2H-5-phenyltetrazoles 11 and 12 is followed by isomerizations of 13 •+ to the phenylcyanamide ion 15 •+ over a low barrier. A cyclization of imidoylnitrene ion 13 •+ onto the benzene ring offers alternate, very facile routes to the phenylnitrene ion 8a •+ and the phenylcarbodiimide ion 14 •+ via the azabicyclooctadienimine 16 •+ . Eliminations of HNC or HCN from 14 •+ and 15 •+ again yield the phenylnitrene radical cation 8a •+ . A direct 1,3-H shift isomerizing phenylcarbodiimide ion 14 •+ to the phenylcyanamide ion 15 •+ requires a very high activation energy of 114 kcal/mol, and this reaction needs not be involved. The benzonitrile imine −3-phenyl-1H-diazirine−phenylimidoylnitrene−phenylcarbodiimide/phenylcyanamide rearrangement has parallels in thermal and photochemical processes, but the facile cyclization of imidoylnitrene 13 •+ to azabicyclooctadienimine 16 •+ is facilitated by the positive charge making the nitrene more electrophilic. Furthermore, the benzonitrile imine radical cation 19 •+ can cyclize to indazole 24 •+ , and a series of intramolecular rearrangements via hydrogen shifts, ring-openings and ring closures allow the interconversion of numerous ions of composition C 7 H 6 N 2•+ , including 19 •+ , 24 •+ , the benzimidazole ion 38 •+ and o-aminobenzonitrile ion 40 •+ , all of which can eliminate either HCN or HNC to yield the C 6 H 5 N •+ ions of phenylnitrene, 8a •+ , and/or iminocyclohexadienylidene, 34 •+ . Moreover, benzonitrile imine 19 •+ can behave like a benzylic carbenium ion, undergoing a novel ring expansion to cycloheptatetraenyldiazene 45 •+ . The N-phenylnitrile imine ion 2d •+ derived from 2-phenyltetrazole 1d cleaves efficiently to the phenylnitrene ion 8a •+ but may also cyclize to the indazole ion 24 •+ . The N-phenylimidoylnitrene 59 •+ derived from 1-phenyltetrazole 5d undergoes facile isomerization to the phenylcyanamide ion 15 •+ and hence phenylnitrene radical cation 8a •+ .

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“…The direct rearrangement of HNCO → HOCN constitutes a 1,3-H shift and requires an activation energy of 98.7 (92.6) kcal/mol. It is endothermic and passes through a transition state TS10 with a nearly linear NCO moiety of the same type as the transition states described for other “linear” 1,3-H shifts, e.g., of aminoacetylene to ketenimine, H 2 N–CCH → HNCCH 2 , and of ketenimine to acetonitrile, H 2 CCNH → H 3 CCN . An IRC graph for the reaction of HNCO → HOCN via TS10 is shown in Figure b.…”

Section: Resultsmentioning

confidence: 84%

CHNO – Formylnitrene, Cyanic, Isocyanic, Fulminic, and Isofulminic Acids and their Interrelationships at DFT and CASPT2 Levels of Theory

Bégué,

Lafargue-Dit-Hauret,

Dargelos

et al. 2023

J. Phys. Chem. A

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Fulminic and cyanic acids played a decisive role in the conception of isomerism 200 years ago. Cyanic (HOCN), isocyanic (HNCO), and fulminic (HCNO) acids have been detected in several interstellar sources, but isofulminic acid (HONC) is little known. Here we examine the interrelationships between the four acids and formylnitrene, HC(O)N, at the CASPT2 and three DFT levels. Formylnitrene has a triplet ground state, T 0 , a closed shell singlet (CSS), S 0 , and an open-shell singlet (OSS), S 1 , lying ∼7 and 27 kcal/ mol above T 0 , respectively. The CSS is weakly stabilized by a 12 kcal/mol bond between the N and the O atoms. A conical intersection 12 kcal/mol above T 0 permits easy T 0 −S 0 interchange. Formyl azide and formylnitrene (T 0 and S 0 ) are isomerized thermally to HNCO. HOCN is best obtained via dissociation of the nitrene (or of HNCO) to H • + NCO • radicals ∼46 kcal/mol above the T 0 nitrene. Isofulminic acid, HONC, isomerizes readily to cyanic acid, HOCN, in thermal and photochemical reactions. Fulminic acid, HCNO, can isomerize to HNCO via CSS formylnitrene. Easy tautomerization prevents the preparation of HOCN in quantity. The barrier to isomerization is strongly reduced in small hydrogen-bonded aggregates so that trace amounts of HOCN can exist in equilibrium with HNCO.

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Ethynamine - Ketenimine - Acetonitrile - Rearrangements: A computational Study of Flash Vacuum Pyrolysis Processes

Cited by 5 publications

References 37 publications

Trimethylsilylnitrene and Its Surprising Rearrangement to N‐(Dimethylsilyl)methanimine via Silaziridine and Silaazomethine Ylide

Trimethylsilylnitrene and Its Surprising Rearrangement to N‐(Dimethylsilyl)methanimine via Silaziridine and Silaazomethine Ylide

Phenylnitrene Radical Cation and Its Isomers from Tetrazoles, Nitrile Imines, Indazole, and Benzimidazole

CHNO – Formylnitrene, Cyanic, Isocyanic, Fulminic, and Isofulminic Acids and their Interrelationships at DFT and CASPT2 Levels of Theory

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