Naphthalene radical cation

Besides a parent ion, the mass spectra of benzo- and dibenzothiepins show the corresponding naphthalene or phenanthrene radical cations as the base peak.2-16 The mass spectra of 1-benzo-thiepin 1-oxides and 1,1-dioxides show the same naphthalene radical cation, formed by loss of sulfur monoxide or sulfur dioxide, respectively.14 In contrast, in the mass spectrum of 2,7-di-terf-butylthiepin peaks resulting from the loss of sulfur are not found.17... 

As an example of the application of the solid-state methods described above, we show the spectra of the naphthalene radical cation in different media236 (Figure 26). Note the increase in spectroscopic resolution and the extension of the range of observation into the UV when using argon matrices. 

Other restricted media in which radical cations of organic substrates are formed are zeolites. Typical anisotropic features of the naphthalene radical cation were observed after exposure of naphthalene to aluminated H ZSM-5 (n = 3, 3.4) calcined under oxygen at 773 K. These spectra contain an overlapping feature, which was assigned to isolated electrons. These signals persist over several weeks at room temperature29. 

A few examples in which aromatic cation radicals have been isolated as crystalline salts, actually consist of mixed valence units. For example, crystal structure analysis showed that the naphthalene radical cation (NAP) + forms a mixed valence dimer (NAPy4 in which the two components are arranged face to face in n-stacks with an interplanar separation significantly closer than van der Waals contacts. Such an intermolecular organization arises from the sponta-... 

Vialaton et al. have reported that irradiation of naphthalene in air saturated aqueous solution produces mainly 7-hydroxy-1,4-naphthoquinone (major), 2-formylcinnamaldehyde, and 2-carboxycinnamaldehyde with a quantum yield of 0.0025 shown in Scheme 1 [7]. They proposed that phototransformation of naphthalene may proceed by a monophotonic ionization process to produce the naphthalene radical cation which can depro-tonate and/or react with water to produce radicals that are oxidized by molecular oxygen to yield the observed 2-formylcinnamaldehyde and 2-carboxycinnamaldehyde. It was further proposed that the formation of 7-hydroxy-1,4-naphthoquinone (major) is likely to result from the photolysis of 1,4-naphthoquinone that can form as an unstable intermediate [8]. 

The SIFT group of Bierbaum at the University of Colorado has also recently been active in the field of ion/atom chemistry, as a facet of their exploration of the IS chemistry of PAH cations. Rate coefficient measurements for reactions of the naphthalene radical cation, C10HJ, the closed shell naphthylium cation,... 

Wilkinson and Schroeder (1979) have shown that the triplet states of aromatic hydrocarbons are quenched by quinones, the efficiency of quenching being related to the electron affinity of the quinone and the ionisation potential of the triplet hydrocarbon (Schroeder and Wilkinson, 1979). It was concluded that the quenching did not involve full electron transfer in nonpolar solvents. Photolysis experiments have shown that in propionitrile tetrachloro-benzo-l,4-quinone reacts with naphthalene to give radical ions (Gschwind and Haselbach, 1979). The naphthalene radical cation reacts with naphthalene to give a detectable intermediate. 

Besides direct electroreduction of PTFE on metal cathode, the indirect dehalogenation was carried out by electrochemically generated reactants. A classical reaction employs naphthalene radical cation, which is generated electrochemically in a solution of naphthalene in dimethylformamide + NBU4BF4 or NBU4CIO4 [50,56] (Eq. 4.20). The radicals react with PTFE while the naphthalene is regenerated (4.20a) and the reaction propagates in a catalytic loop ... 

Predict the shift of the first absorption band of naphthalene radical cation upon 1-methyl substitution. [0.4252 (—0.333)/3 = 0.06)3, hypsochromic shift, ref. 291]... 

Quenching of the excited state of U02 by naphthalene can occur along two parallel pathways, exciplex formation and electron transfer to give the naphthalene radical cation In the presence of molecular oxygen, CeHg is... 

The mass spectra of 1-benzothiepines are reported to show an appreciable intensity for the parent ion and have the corresponding naphthalene radical cations as the base peak <73JOC3978>. A publication in 1989 has shown a peak at mjz 134 (M" — C2H2) to be observed, besides the parent ion and the ion attributed to naphthalene radical cation generated by loss of sulfur in the mass spectrum of 1-benzothiepine (2) <89ZN(B)220>. 

As it was first shown on naphthalene radical cation salts of various aromatic hydrocarbons can be prepared by anodic oxydation and subsequent crystallization in solvents like methylenechloride, chlorobenzene, 1,1,2-trichloroethane or THF if an electrolyte like NR4X with suitable anions X is present (R n-hutyl X BF4, C104, PF5 , AsF6% SbF6, ...) l... 

Fig. 8 Modelling black) of the experimental IRMPD spectrum [150] (green) of the naphthalene radical cation. The redshift of the main absorption band and the intensity enhancement of the minor band in the IRMPD spectrum as compared to the linear spectrum (red) are satisfactorily modelled based upon the model of Pameix et al. and DPT computed anharmonic parameters. Reproduced from Pameix et al., J Phys Chem A, 2013 [171]...

These models can reasonably describe the typical features of experimental IRMPD spectra such as the observed bandwidths (typically >20 cm ) and frequency shifts (typically a few %). More system-specific effects are also evident from such modelling. For instance, shifting of the absorption profile during MPE (see Fig. 7) may cause nearby absorptions in the IR spectrum to become resonant during the excitation process, which can induce a second burst of absorption and lead to severe deviations from relative band intensities in a linear absorptitMi spectrum [171, 179]. An example is shown in Fig. 8, where a weak absorption in the linear IR spectrum of the naphthalene radical cation is amplified in the IRMPD spectrum because of the nearby strong absorption band, as correctly modelled by Pameix et al. [171]. 

In this context, laser flash photolysis studies have provided clear evidence for the generation of naphthalene radical cations (X ,3x of 380 and 600 nm). Addition of increasing amounts of CCI4 in the photolysis of 6-methoxy-2-naphthylacetic acid results in fluorescence quenching, together with enhanced generation of the radical cation and a higher efficiency of the photodecarboxylation process. ... 

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