- Diazodiphenylmethane and monosubstituted butadienes: Kinetics and a new chapter of vinylcyclopropane chemistry
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Diazodiphenylmethane (DDM) undergoes cycloadditions to 1-substituted buta-1,3-dienes exclusively at the C(3)=C(4) bond. At room temperature, the N2 loss from the initially formed 4,5-dihydro-3H-pyrazoles 2 is faster than the cycloaddition and furnishes the vinylcyclopropane derivatives 7 and 9 with structural retention at the C(1)=C(2) bond. 2-Substituted butadienes react with DDM at the C(3)=C(4) bond to give 12; isoprene, however, affords 3,4/1,2 products in the ratio of 86:14. DDM is a nucleophilic 1,3-dipole: 1-Cyanobutadiene reacts 400 times faster than 1-methoxybuta-1,3-diene (DMF, 40°). The log k2 for the additions to six 1-substituted butadienes show a linear correlation with σp (Hammett) and ρ = +2.9; the log k2 of five 2-substituted butadienes are linearly related to Taft's σI (ρ = +1.7). The structures of the vinylcyclopropanes 7, 9, and 12 are established by NMR spectra and oxidation. A cyclopropyl carbinyl cation is made responsible for the isomerization of 12, R = Ph, Me, by acetic acid to 4-substituted 1,1-diphenylpenta-1,3-dienes 25 and 29; TsOH at 200° converts 25 further to 9,10-dihydro-9-methyl-10-phenyl-9,10-ethanoanthracene (27). Thermal rearrangement of 7, 9, and 12 at 200-300° produces the 3- or 1-substituted 4,4-diphenylcyclopentenes 30 and 31. These give the same mass spectra as the vinylcyclopropanes, and an open-chain distonic radical cation is suggested as common intermediate. Besides spectroscopic evidence for the cyclopentene structures, hydrogenation and epoxidation are described; NMR data support the trans-attack by perbenzoic acid.
- Ohta, Akihiro,Dahl, Klaus,Raab, Rainer,Geittner, Jochen,Huisgen, Rolf
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scheme or table
p. 783 - 804
(2009/03/11)
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- Structural Control of the Triplet-Singlet Equilibrium in Cyclophane Diarylcarbenes
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The absolute reactivities of paracyclophane analogues of diphenylcarbene have been investigated by using the technique of laser flash photolysis.The results are consistent with theoretical predictions that the relative stabilities of the triplet and singlet states of these species can be controlled by changing the hybridization at the carbenic center and the torsional angle of the aryl rings.
- Alt, R.,Gould, I. R.,Staab, H. A.,Turro, N. J.
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p. 6911 - 6914
(2007/10/02)
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- TEMPERATURE DEPENDENCE OF THE REACTIONS OF SINGLET AND TRIPLET DIPHENYLCARBENE. EVIDENCE FOR REVERSIBLE YLIDE FORMATION IN THE REACTION WITH ALCOHOLS
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The temperature dependences of the reaction of singlet diphenylcarbene are consistent with reversible intermediate formation.
- Turro, Nicholas J.,Cha, Yuan,Gould, Ian R.
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p. 5951 - 5954
(2007/10/02)
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- SINGLET-TRIPLET INTERCONVERSION OF DIPHENYLMETHYLENE. ENERGETICS, DYNAMICS AND REACTIVITIES OF DIFFERENT SPIN STATES
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A combination of picosecond and nanosecond laser spectroscopy measurements, chemical quenching experiments and triplet sensitization experiments has allowed the determination of the rapid singlet to triplet and slower triplet to singlet intersystem crossing rates for diphenylmethylene in fluid solution at room temperature.It is shown that under the conditions of the kinetic measurements, singlet and triplet diphenylmethylene (1DPM and 3DPM, respectively) are in rapid equilibrium relative to reactions, so that knowledge of the values of kST and kTS allows determination of the equilibrium constant and change in free energy for the 1DPM*3DPM process.The absolute reactivity of 1DPM toward a series of alcohols has been determined and is discussed in terms of other current investigations of carbene reactivity.
- Eisenthal, K. B.,Turro, N. J.,Sitzmann, E. V.,Gould, I. R.,Hefferon, G.,et al.
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p. 1543 - 1554
(2007/10/02)
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- LASER FLASH SPECTROMETRIC INVESTIGATIONS OF BIRADICALS AND CAGED RADICAL PAIRS
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The use of laser flash spectroscopic techniques allows the detection, identification and dynamic analysis of biradicals and caged radical pairs in fluid solution at ambient temperatures.The conventional flash spectroscopic device has been advanced with the advent of the Excimer Laser, as an excitation source of the optical multichannel analyzer (OMA) as a detector system and of the transient digitizer (TD) as a data collector and analyzer.The Excimer Laser, in addition to serving as an excitation source, may also induce novel photophysical and/or photochemical events as a result of the unusually high intensities produced by such devices.Examples are given of the use of Excimer Laser-OMA and Excimer Laser-TD systems to study the dynamics of radical pairs that are caged in micelle aggregates and to study novel emissions produced by photoexcitation of benzophenone and substituted benzophenones.
- Turro, Nicholas J.
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p. 809 - 817
(2007/10/02)
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