Electron Transfer Photochemistry of Norbornadiene and Quadricyclane. Nucleophilic Capture of Radical Cations, Free-Radical Rearrangements, and Hydrogen Abstraction

Weng, Hengxin; Roth, Heinz D.

doi:10.1021/jo00118a034

Cited by 35 publications

(35 citation statements)

References 3 publications

(4 reference statements)

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“…The reaction products were compatible with the intermediacy of radical cations, N Á and Q Á , nucleophilic capture from the exo-face and rearrangements of and hydrogen abstraction by the resulting free radicals. 10 Our study showed substantial disagreement with an earlier report describing the donor-acceptor photochemistry of 1-cyanonaphthalene (CNN) with N or Q in methanol. 11 We observed much lower yields of methanol adducts, 1-3, and isolated a different product type, containing both methoxy and cyanophenyl substituents.…”

Section: Introductioncontrasting

confidence: 99%

“…10 The sensitizer, CNN, was consumed and two types of molecular adducts were formed. Adducts containing N and CNN in a ratio of 1:1 were formed in ca 55% combined yield, (exo-[2 2]-adducts 4-7 50%; a meta-addition adduct 8, ca 6%).…”

Section: Resultsmentioning

confidence: 99%

“…In addition, minor amounts of acetoni-trile adducts and trace amounts of adducts containing N and CH 3 OH in a ratio of 2:1 were observed. 10 The metaadduct (3% yield) was again detected based on its characteristic GC-MS behavior.…”

Section: Resultsmentioning

confidence: 99%

“…We were able to isolate and characterize five products, 9a-11, which were obtained in yields between 5% (9a) and 2% (10). Similarly to the [2 2]-adducts 4-7, their NMR spectra show the general features characteristic for a 5,6-disubstituted norbornene unit.…”

Section: Cycloaddition Productsmentioning

confidence: 95%

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Stereospecific nucleophilic trapping of encounter complexes between photoexcited 1-cyanonaphthalene and norbornadiene

Weng

Roth

1998

J. Phys. Org. Chem.

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Photo-induced electron donor-acceptor reactions between 1-cyanonaphthalene (CNN) and norbornadiene (N) generate products of several structure types. Methanol adducts (1-3) formed in polar solvents are rationalized via the radical cation, N Á , and stereospecific (exo-) nucleophilic attack by methanol. In less polar solvents, CNN and N form [2 + 2]-cycloadducts, exclusively on the exo-face of N. In non-polar solvents containing methanol, CNN, N and methanol combine to form 1:1:1 adducts, containing the sensitizer on the endo-and the methoxy groups on the exo-face. The formation of these products is rationalized via the trapping of encounter complexes of different geometries. Any rearrangement of the norbornenyl system can be eliminated, since neither tricyclyl nor 7-methoxynorbornenyl structures are formed. Apparently, the alcohol captures an endo-encounter complex of CNN and N by attack from the exo-face, similar to the attack of methanol on N Á .

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Section: Introductioncontrasting

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Cycloaddition Productsmentioning

confidence: 95%

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Stereospecific nucleophilic trapping of encounter complexes between photoexcited 1-cyanonaphthalene and norbornadiene

Weng

Roth

1998

J. Phys. Org. Chem.

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“…11 The unusual reactivity of the system is due to this ring strain and generally results in cleavage of one or both of the C 2 -C 6 and C 3 -C 5 cyclopropyl bonds. QC readily undergoes photochemically, 12 electrochemically, 13 and chemically 14 initiated conversion to its lower energy valence isomer, norbornadiene (NB).…”

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confidence: 99%

An Electrochemical and Fourier Transform Infrared Spectroscopic Study of the Aqueous Oxidation of Quadricyclane and Nortricyclanol

White

Buttry

2000

J. Electrochem. Soc.

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The compound quadricyclo(2.2.1.0 2,6 .0 3,5 )heptane, more commonly referred to as quadricyclane (QC), has enjoyed a rich history of chemical investigation. From its initial discovery in 1936, 1 it has been considered for use as a solar energy storage medium, 2 an optical computer memory system, 3 and most recently, and perhaps most realistically, as a high energy aviation fuel. 4 Although several studies have been conducted concerning the nonaqueous chemistry of QC, including its valence isomerization to norbornadiene, [5][6][7][8][9] little is known about the chemistry that might be expected should QC be released into the (aqueous) environment. 10 The study of QC and its isomers by electrochemical means allows for careful assessment of the relevant redox chemistry in a timely fashion, as these processes occur very slowly under typical environmental conditions. The issue of release into the environment is of major concern given the possibility of its use as an aviation fuel additive. Toward this end, we report here a study of the aqueous redox chemistry of QC and nortricyclanol, a hydrolysis product that is readily formed when QC is present in aqueous solutions.QC is a seven-membered carbon quadricycle containing two cyclopropyl, one cyclobutyl, and two cyclopentyl rings (Scheme 1). The compound is a stable liquid at room temperature with a fairly high vapor pressure under normal conditions (bp 108ЊC at 740 mm Hg). The strain energy has been reported as approximately 340 kJ mol Ϫ1 . 11 The unusual reactivity of the system is due to this ring strain and generally results in cleavage of one or both of the C 2 -C 6 and C 3 -C 5 cyclopropyl bonds. QC readily undergoes photochemically, 12 electrochemically, 13 and chemically 14 initiated conversion to its lower energy valence isomer, norbornadiene (NB).There is a relatively high thermal barrier for the conversion of QC to NB (385 kJ mol Ϫ1 ), 15 which can be overcome with irradiation in the presence of a sensitizer. The conversion of QC to NB is achieved easily through a free-radical chain reaction. The initiation of this chain reaction is a one-electron oxidation to form the QC ϩ• radical cation, which quickly rearranges to the NB ϩ• radical cation. This species forms NB by oxidation of an additional QC molecule, in a step that generates another QC ϩ• radical cation, thus continuing the propagation. 15 Until recently, the structures and number of intermediates in this conversion were unknown. Through the use of chemically induced dynamic nuclear polarization (CIDNP) experiments, 16 Roth and Schilling were able to verify the existence of both the elusive QC ϩ• and the longer-lived NB ϩ• cation radicals. Very rapid isomerization of QC ϩ• to NB ϩ• precluded the direct spectroscopic observation of QC ϩ• until time-resolved electron spin resonance spectroscopy 17 was enlisted in the search. Turro et al. established the lifetime of QC ϩ• to be ϳ10 Ϫ6 s (with a thermal barrier of 38 kJ mol Ϫ1 for conversion to NB ϩ• ) 15 and also used laser flash photolysis and time-resol...

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Common Radical Cation Intermediates in Cage Hydrocarbon Activations

et al. 1999

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The oxidation of 3,6‐dehydrohomoadamantane (1) was achieved under chemical (NO+BF4–/EtOAc, NO+OAc–/Ac2O, and NO+BF4–/CH3CN), photochemical (photoexcited 1,2,4,5‐tetracyanobenzene), and electrochemical (Pt anode, CH3CN, NH4BF4) conditions. Supporting ab initio [density functional theory (BLYP) and Møller–Plesset perturbation theory (MP2)] computations utilizing standard basis sets, 6–31G* (optimizations) and 6–311+G* (single‐point energy evaluations), agree with the experimental results implicating the involvement of the same radical cation intermediates in the activation processes. Isomeric radical cations formed from different precursors can equilibrate with low barriers (2.0–11.7 kcal mol–1) and lead to common products. The computed and experimental adiabatic ionization potential of adamantane shows that activation with NO+BF4– is also likely to occur through the adamantyl radical cation. Hence, the bonds need not be attacked directly by the electrophile in the C–H or C–C activation of alkanes with relatively low ionization potentials.

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Electron Transfer Photochemistry of Norbornadiene and Quadricyclane. Nucleophilic Capture of Radical Cations, Free-Radical Rearrangements, and Hydrogen Abstraction

Cited by 35 publications

References 3 publications

Stereospecific nucleophilic trapping of encounter complexes between photoexcited 1-cyanonaphthalene and norbornadiene

Stereospecific nucleophilic trapping of encounter complexes between photoexcited 1-cyanonaphthalene and norbornadiene

An Electrochemical and Fourier Transform Infrared Spectroscopic Study of the Aqueous Oxidation of Quadricyclane and Nortricyclanol

Common Radical Cation Intermediates in Cage Hydrocarbon Activations

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