The IR spectrum of triplet phenylnitrene. On the origin of didehydroazepine in low temperature matrices

Hayes, James C.; Sheridan, Robert S.

doi:10.1021/ja00171a038

Cited by 108 publications

(105 citation statements)

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“…Note that a benzazirine analogous to 6 was not detected upon photolysis of phenyl azide in an Ar matrix. 31,32 As seen in Fig. 1, the electronic absorption (EA) spectrum of triplet nitrene 4 is well reproduced by CASSCF/CASPT2 calculations.…”

Section: Resultssupporting

confidence: 53%

Matrix isolation and computational study of the photochemistry of p-azidoaniline

Pritchina

Gritsan

Bally

2006

Phys. Chem. Chem. Phys.

152

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The photochemistry of p-azidoaniline was studied in argon matrices in the absence and presence of oxygen. With the help of quantum chemical calculations we were able to characterize the triplet p-aminophenylnitrene as well as the cis-and trans-p-aminophenylnitroso oxides. It was found that the latter two isomers can be interconverted by selective irradiation and that they are ultimately converted into p-nitroaniline. Although restricted wavefunctions of the nitroso oxides are unstable, CASSCF calculations turned up no evidence for the claimed diradical character of these compounds. Also we found no evidence for dioxaziridines as intermediates of the conversion of the nitroso oxides to p-nitroaniline. IntroductionGreat progress has been made in understanding the photochemistry of aryl azides over the past few years. 1,2 Singlet phenylnitrene and a series of its simple derivatives have been detected directly and the effects of substituents on the spectra and the decay kinetics of singlet aryl nitrenes have been examined systematically. 2 Thereby it was found that groups which act as strong p donors dramatically accelerate the rate of intersystem crossing. This could be the reason why photolysis of p-azidoaniline (1) and p-azidodimethylaniline, unlike that of phenyl azide and most of its derivatives, gives only products of triplet nitrene reactions. 3,4 For instance, in the presence of oxygen at ambient temperature p-nitroaniline (2) and p-nitrosoaniline (3) are formed in quantitative yield upon photolysis of 1 (Scheme 1). 3,5 Since the early seventies it has been known that triplet arylnitrenes react with oxygen by formation of adducts. [5][6][7][8][9] In an early study on 1,4-diazidobenzene, two types of adducts (diamagnetic and paramagnetic) were detected in glassy matrices. 6 It was proposed that the diamagnetic adduct is an arylnitroso oxide, R-NQO 1 -O À , and the paramagnetic species is a ''spin isomer'' thereof, the triplet aryliminodioxy diradical, R-N-O -O . 6,10 Although subsequent studies did not confirm the formation of triplet adducts of arylnitrenes with oxygen, 3,5,7,8 speculations about the occurrence of aryliminodioxy diradicals in the photooxidation of aryl azides continue to surface occasionally in the literature. 11 This paper is devoted to a comprehensive experimental and computational study of the reactions of triplet arylnitrenes with oxygen in order to unambiguously identify the resulting adducts by their experimentally observed spectra, and to understand their properties. It should be noted that the earlier assignments of a strong near-UV absorption to arylnitroso oxides 3,5,7-9 were never supported by calculations. p-Azidoaniline was used in our matrix isolation study because, as noted above, it gives exclusively products of triplet nitrene reactions in solution, and we thought that this would also simplify the photochemistry in Ar matrices. In addition, the reaction of triplet p-aminophenylnitrene (4) with oxygen in solution and in glassy matrices has previously been studied. 5 2 Experim...

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Section: Resultssupporting

confidence: 53%

Matrix isolation and computational study of the photochemistry of p-azidoaniline

Pritchina

Gritsan

Bally

2006

Phys. Chem. Chem. Phys.

152

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“…Prolonged UV irradiation produces ketenimine 6 d' with the characteristic broad C=C=N stretching vibration [9] at 1878.1 cm…”

Section: Resultsmentioning

confidence: 99%

3,4,5,6‐Tetrafluorophenylnitren‐2‐yl: A Ground‐State Quartet Triradical

Grote

Finke

Koßmann

et al. 2010

Chemistry A European J

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The photochemistry of 2-iodo-3,4,5,6-tetrafluorophenyl azide (7 d) has been investigated in argon and neon matrices at 4 K, and the products characterized by IR and EPR spectroscopy. The primary photochemical step is loss of a nitrogen molecule and formation of phenyl nitrene 1 d. Further irradiation with UV or visible light results in mixtures of 1 d with azirine 5 d', ketenimine 6 d', nitreno radical 2 d, and azirinyl radical 9. The relative amounts of these products strongly depend on the matrix and on the irradiation conditions. Nitreno radical 2 d with a quartet ground state was characterized by EPR spectroscopy. Electronic structure calculations in combination with the experimental results allow for a detailed understanding of the properties of this unusual new type of organic high-spin molecules.

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“…Once formed, the triplet nitrene can absorb a second photon and regain the singlet manifold by intersystem crossing. 11 It has thus been shown that virtually all of the original azide will be converted to the aza- cycloheptatetraene, unless carefully selected monochromatic light is used for the photolysis.…”

Section: Introductionmentioning

confidence: 99%

4H-Azepin-4-ones from 4-azidophenols in low-temperature matrices

Dunkin¹,

Gallivan²,

Lynch³

1997

J. Chem. Soc., Perkin Trans. 2

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In an attempt to develop a synthetic approach to 4H-azepin-4-ones in exceptionally mild conditions, 4-azidophenols have been photolysed in N 2 matrices at 12-14 K and subjected to flash vacuum pyrolysis (FVP) with subsequent trapping of the products in N 2 matrices. The reactions were followed by IR spectroscopy. The compounds studied were 4-azidophenol, which was prepared in a purer form than achieved by earlier workers, 4-azido-2-nitrophenol, the previously unknown 2,6-dichloro and 2,6-dibromo and 2-chloro-6-methyl derivatives of 4-azidophenol, and a heterocyclic analogue, 5-azido-8-hydroxyquinoline. In all cases, IR spectra indicated that the expected ring expansion to give azepinones occurred, while in some conditions intermediate hydroxyazacyclohepta-1,2,4,6-tetraenes could also be detected. For several of the azidophenols, photolyses and pyrolyses were attempted on a larger scale (50 mg or more) in a specially constructed low-temperature cell. These reactions were monitored by diffuse reflection IR spectroscopy (DRIFTS), which showed that the desired azepinones were formed at low temperature. Attempts to isolate the azepinones by warming to room temperature, however, resulted only in polymeric products. Preparative scale pyrolyses in conventional FVP equipment also gave polymers.

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The IR spectrum of triplet phenylnitrene. On the origin of didehydroazepine in low temperature matrices

Cited by 108 publications

References 0 publications

Matrix isolation and computational study of the photochemistry of p-azidoaniline

Matrix isolation and computational study of the photochemistry of p-azidoaniline

3,4,5,6‐Tetrafluorophenylnitren‐2‐yl: A Ground‐State Quartet Triradical

4H-Azepin-4-ones from 4-azidophenols in low-temperature matrices

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