Direct Observation of Singlet Phenylnitrene and Measurement of Its Rate of Rearrangement

Gritsan, Nina P.; Yuzawa, Tetsuro; Platz, Matthew S.

doi:10.1021/ja963753n

Cited by 104 publications

(119 citation statements)

References 32 publications

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“…Figure 6 displays the typical kinetics of the decay of singlet 2-fluorophenylnitrene (2b) and the formation of products (ketenimine 4b and triplet nitrene 6b) at different temperatures. All other substituted singlet phenylnitrenes studied in this work and previously 23,26,33 exhibited rates of nitrene decay that were equal to the rates of product formation. At low temperatures where triplet nitrenes are formed in higher yields, slow growths in absorption similar to those displayed in Figure 6G were observed on microsecond time scales due to triplet nitrene dimerization to form azobenzenes which absorb in the UV region.…”

Section: Resultssupporting

confidence: 70%

“…The spectrum of singlet nitrene 2b is similar to the spectra of singlet 2,6-difluorophenylnitrene (2e) ( Figure 1, spectrum 1) and parent singlet phenylnitrene 2a. 8,23 Unique kinetic results were obtained upon LFP of azide 1b. Figure 6 displays the typical kinetics of the decay of singlet 2-fluorophenylnitrene (2b) and the formation of products (ketenimine 4b and triplet nitrene 6b) at different temperatures.…”

Section: Resultsmentioning

confidence: 97%

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A Laser Flash Photolysis and Quantum Chemical Study of the Fluorinated Derivatives of Singlet Phenylnitrene

et al. 2001

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Laser flash photolysis (LFP, Nd:YAG laser, 35 ps, 266 nm, 10 mJ or KrF excimer laser, 10 ns, 249 nm, 50 mJ) of 2-fluoro, 4-fluoro, 3,5-difluoro, 2,6-difluoro, and 2,3,4,5,6-pentafluorophenyl azides produces the corresponding singlet nitrenes. The singlet nitrenes were detected by transient absorption spectroscopy, and their spectra are characterized by sharp absorption bands with maxima in the range of 300-365 nm. The kinetics of their decay were analyzed as a function of temperature to yield observed decay rate constants, k(OBS). The observed rate constant in inert solvents is the sum of k(R) + k(ISC) where k(R) is the absolute rate constant of rearrangement of singlet nitrene to an azirine and k(ISC) is the absolute rate constant of nitrene intersystem crossing (ISC). Values of k(R) and k(ISC) were deduced after assuming that k(ISC) is independent of temperature. Barriers to cyclization of 4-fluoro-, 3,5-difluoro-, 2-fluoro-, 2,6-difluoro-, and 2,3,4,5,6-pentafluorophenylnitrene in inert solvents are 5.3 +/- 0.3, 5.5 +/- 0.3, 6.7 +/- 0.3, 8.0 +/- 1.5, and 8.8 +/- 0.4 kcal/mol, respectively. The barrier to cyclization of parent singlet phenylnitrene is 5.6 +/- 0.3 kcal/mol. All of these values are in good quantitative agreement with CASPT2 calculations of the relative barrier heights for the conversion of fluoro-substituted singlet aryl nitrenes to benzazirines (Karney, W. L. and Borden, W. T. J. Am. Chem. Soc. 1997, 119, 3347). A single ortho-fluorine substituent exerts a small but significant bystander effect on remote cyclization that is not steric in origin. The influence of two ortho-fluorine substituents on the cyclization is pronounced. In the case of the singlet 2-fluorophenylnitrene system, evidence is presented that the benzazirine is an intermediate and that the corresponding singlet nitrene and benzazirine interconvert. Ab initio calculations at different levels of theory on a series of benzazirines, their isomeric ketenimines, and the transition states converting the benzazirines to ketenimines were performed. The computational results are in good qualitative and quantitative agreement with the experimental findings.

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Section: Resultssupporting

confidence: 70%

Section: Resultsmentioning

confidence: 97%

A Laser Flash Photolysis and Quantum Chemical Study of the Fluorinated Derivatives of Singlet Phenylnitrene

et al. 2001

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“…Figure 11.7 also demonstrates the electronic absorption spectrum of ketenimine 51 (spectrum 2), recorded on a nanosecond time scale at ambient temperature. 195 The assignment of the transient absorption in Figure 11.7 to the 1 52 was supported by the calculation of its electronic absorption spectrum. Indeed, the spectrum of 1 52 ( 1 A 2 ) calculated at the CASPT2 level is in good agreement with the transient spectrum of Figure 11.7 .…”

Section: Photochemistry Of Phenyl Azidementioning

confidence: 73%

Photochemistry of Azides: The Azide/Nitrene Interface

Gritsan

Platz

2009

Organic Azides

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“…In regard to the latter, they can be used as photoaffinity labels for biomolecules, [3,4] photoresist linking agents, [5] and in the preparation of light activated polymer surfaces [6,7]. In regard to the former, the course of photochemical decomposition of phenyl azides has been established by laser flash photolysis (LFP) methods [8][9][10][11][12] and both time-resolved infrared [13] and Raman [14] spectroscopy to proceed via the singlet nitrene, which may undergo either a rapid ring expansion reaction to form didehydroazepine or intersystem crossing (ISC) to form the triplet which subsequently dimerizes [8][9][10][11][12]. At ambient temperatures, singlet phenyl nitrenes have lifetimes of about 1 ns.…”

Section: Introductionmentioning

confidence: 99%

Synthesis, properties and X‐ray structure of 5‐azido‐2‐methoxy‐1,3‐xylyl‐18‐crown‐5

Yonekawa¹,

Goodpaster²,

Abel³

et al. 2006

Journal of Heterocyclic Chem

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5-Azido-2-methoxy-1,3-xylyl-18-crown-5 has been prepared by reacting p-toluenesulfonyl azide with the carbanion generated from the reaction of 5-bromo-2-methoxy-1,3-xylyl-18-crown-5 with n-butyl lithium. The asymmetric N 3 stretch of this product has been observed as a single band at 2110 cm -1 in dichloromethane solution. Addition of solid NaSCN, KSCN and CsSCN shifts this band to 2115, 2113 and 2112 cm -1 , respectively. Computational studies of this azide at the B3LYP-6-31G* level in the presence and absence of Na + predicted these bands to be at 2173 cm -1 and 2184 cm -1. For the salt-containing solutions, additional bands were observed at 2066 cm -1 , 2056 cm -1 and 2055 cm -1 , respectively, which are in the range expected for CN stretches. The X-ray structure of this azide has been determined. The terminal and internal N-N bond lengths were found to be 1.127(2) and 1.245(2) , respectively, which is the usual pattern for aromatic azides. The crown ether is looped over the face of the aromatic ring resulting in an angle of 38.94° between the plane defined by the aromatic ring and that defined by the five ring oxygen atoms. In addition, the CH 3 group is rotated out of the plane of the phenyl ring with C1-C18-O181-C182 and C17-C18-O181-C182 dihedral angles of 93.81(14)° and -90.54(14)°, respectively.

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Direct Observation of Singlet Phenylnitrene and Measurement of Its Rate of Rearrangement

Cited by 104 publications

References 32 publications

A Laser Flash Photolysis and Quantum Chemical Study of the Fluorinated Derivatives of Singlet Phenylnitrene

A Laser Flash Photolysis and Quantum Chemical Study of the Fluorinated Derivatives of Singlet Phenylnitrene

Photochemistry of Azides: The Azide/Nitrene Interface

Synthesis, properties and X‐ray structure of 5‐azido‐2‐methoxy‐1,3‐xylyl‐18‐crown‐5

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