Laser Flash, Laser-Drop, and Lamp Photolysis of 1,3-Dichloro-1,3-diphenylpropane. One- <i>versus</i> Two-Photon Reaction Pathways

Miranda, Miguel A.; Pérez‐Prieto, Julia; Font‐Sanchis, Enrique; Kónya, Klára; Scaiano, J. C.

doi:10.1021/jo9704772

Cited by 15 publications

(14 citation statements)

References 27 publications

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“…The signal at 360 nm is consistent with the formation of the 1,3-diphenyl-2propenyl radical (9, λ max 360 nm) produced from the 3-chloro-1,3-diphenylpropyl radical (8, λ max 320 nm), according to the mechanism of Scheme 3, which we have already established in the case of cyclohexane as solvent. 10,18 Thus, photolysis of 1 in acetonitrile produced both the propenyl radical 9 and the propenyl cation 3. Clearly, the homolytic cleavage can involve two-photon processes under conditions where the heterolytic cleavage does not; this is consistent with the strong absorption of the benzylic radicals at the laser wavelength, as already noted in the case of nonpolar solvents.…”

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confidence: 99%

Flash Photolysis of 1,3-Dichloro-1,3-diphenylpropane in Polar Solvents: Generation of a Stabilized γ-Chloropropyl Cation, Subsequent Formation of a Propenyl Cation, and Nucleophilic Trapping of Both Cations

et al. 1998

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Photolysis of 1,3-dichloro-1,3-diphenylpropane (1) in 2,2,2-trifluoroethanol at 266 nm leads to a γ-chloropropyl cation (2a) following loss of chloride ion. Kinetic evidence has been obtained for the interconversion between the open chain cation and the corresponding cyclic chloronium ion (2b); thermal loss of hydrogen chloride gives the 1,3-diphenyl-2-propenyl cation (3). The formation of this species occurs through a monophotonic process; the involvement of a two-photon process in the photoheterolysis of dihalide 1 has been ruled out by studying the formation of cation 3 from 1 at different laser intensities. The lack of power dependence implies that 3-chloro-1,3-diphenylpropene (4) is not an intermediate in the photoheterolysis of dihalide 1. The reaction of both cationic intermediates (2 and 3) with different nucleophiles has also been examined. Finally, two-laser two-photon experiments have allowed the study of the photoisomerization of E,E-3 into Z,E-3.

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Section: Resultsmentioning

confidence: 99%

Flash Photolysis of 1,3-Dichloro-1,3-diphenylpropane in Polar Solvents: Generation of a Stabilized γ-Chloropropyl Cation, Subsequent Formation of a Propenyl Cation, and Nucleophilic Trapping of Both Cations

et al. 1998

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“…5 Actually, a new spectrum obtained under these conditions showed a higher ratio of radical 2a to the two photon intermediate, 3a (Fig. 1).…”

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“…When irradiating with a 266 nm laser it is useful to place a beam diffuser (which eliminates 'hot' spots in the laser beam) close to the sample in order to get a better observation of monophotonic transients. 5 Actually, a new spectrum obtained under these conditions showed a higher ratio of radical 2a to the two photon intermediate, 3a (Fig. 1).…”

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Mechanistic studies on the photogeneration of o- and p-xylylenes from α,α′-dichloroxylenes

Miranda¹,

Font‐Sanchis²,

Pérez‐Prieto³

et al. 1998

Chem. Commun.

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Two-colour two-laser techniques have unambiguously proved that photolysis of the o-/p-(chloromethyl)benzyl radical leads to the sequential two-photon generation of o-/pxylylene from a,aA-dichloro-o-/p-xylene.Xylylenes are molecules of considerable theoretical and synthetic interest, which have been detected and characterized by different spectroscopic methods. 1 Although benzylic dichlorides have been used as very simple and readily accessible precursors, the involved mechanisms are not completely understood. 2 It has been recently reported 3 that 266 nm laser irradiation of a,aA-dichloro-o-xylene (1a) produces the dissociation of both C-X bonds via a two-photon process; however, the nature of the intermediate species which absorbs the second photon is uncertain. Three possibilities have been considered: the S 1 and T 1 states of 1a and the o-(chloromethyl)benzyl radical (2a). Based on the short lifetime of the singlet state of the dichloride and the apparent relative yields of the observed transients, the undetected T 1 state of the dichloride has been suggested as the photochemical precursor of o-xylylene.Our aim was to explore the photochemistry of the benzyl radical 2a produced after dissociation of one C-X bond of a,aAdichloro-o-xylene, using two-laser two-colour techniques, in order to obtain new data to support or reject the intermediacy of 2a in the formation of o-xylylene. We report here our findings and compare them with those obtained in the photolysis of a,aAdichloro-p-xylene. Based on the obtained results, a mechanism for the formation of o-and p-xylylenes from their corresponding dichloro precursors is presented.Laser flash photolysis of deaerated 1.5 mm solutions of 1a in cyclohexane at 266 nm (Nd: YAG laser, fourth harmonic, < 10 ns, @20 mJ pulse 21 ) yielded the transient absorption spectra shown in Fig. 1. Two transients with different lifetimes were obtained. According to the literature, 3 they were assigned to 2a (with a maximum at 330 nm) and o-xylylene (3a) (maximum at 360 nm, e max = 3 3 10 3 dm 3 mol 21 cm 21 ), 4 generated through one-and two-photon processes, respectively.When irradiating with a 266 nm laser it is useful to place a beam diffuser (which eliminates 'hot' spots in the laser beam) close to the sample in order to get a better observation of monophotonic transients. 5 Actually, a new spectrum obtained under these conditions showed a higher ratio of radical 2a to the two photon intermediate, 3a (Fig. 1).To confirm the radical nature of the transient at 330 nm, oxygenated samples were examined, showing that, while the band at 330 nm was quenched at close to the diffusion controlled limit (see insert Fig. 1), the lifetime of the transient at 360 nm appeared insensitive to the presence or absence of oxygen (data not shown).Furthermore, to study the photobehaviour of 2a, two-colour two-laser flash photolysis experiments 6 were carried out using 266 nm laser pulses (20 mJ pulse 21 ) to photolyze 1a and a 308 nm excimer laser (90 mJ pulse 21 ) to irradiate 2a. The two pulses were ty...

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“…We have previously reported that photolysis of dichlorodiphenylalkanes 1 ( n = 1−3) in cyclohexane produces homolysis of one carbon−halogen bond (Scheme ) . Laser flash photolysis experiments have demonstrated the formation of chloroalkyl radicals 3 , which have the characteristic narrow absorption at 320 nm and are readily quenched by oxygen at close to the diffusion-controlled limit; these are common features of benzylic radicals .…”

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Five-Membered-Ring 9-I-2 Radicals: Direct Detection and Comparison with Other Hypervalent Iodine Radicals

et al. 1999

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Laser Flash, Laser-Drop, and Lamp Photolysis of 1,3-Dichloro-1,3-diphenylpropane. One- versus Two-Photon Reaction Pathways

Cited by 15 publications

References 27 publications

Flash Photolysis of 1,3-Dichloro-1,3-diphenylpropane in Polar Solvents: Generation of a Stabilized γ-Chloropropyl Cation, Subsequent Formation of a Propenyl Cation, and Nucleophilic Trapping of Both Cations

Flash Photolysis of 1,3-Dichloro-1,3-diphenylpropane in Polar Solvents: Generation of a Stabilized γ-Chloropropyl Cation, Subsequent Formation of a Propenyl Cation, and Nucleophilic Trapping of Both Cations

Mechanistic studies on the photogeneration of o- and p-xylylenes from α,α′-dichloroxylenes

Five-Membered-Ring 9-I-2 Radicals: Direct Detection and Comparison with Other Hypervalent Iodine Radicals

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