Femtosecond dynamics of diradicals: transition states, entropic configurations and stereochemistry

Feyter, Steven De; Diau, Eric Wei Guang; Scala, Alfred A.; Zewail, Ahmed H.

doi:10.1016/s0009-2614(99)00263-8

Cited by 45 publications

(40 citation statements)

References 31 publications

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“…These values are significantly lower than those reported for trapping of comparable carbon-centred monoradicals with 17 (4.6ϫ10 8 , 1.9ϫ10 8 and 6.2ϫ10 7 s Ϫ1  Ϫ1 for benzyl, α-methylbenzyl and α,α-dimethylbenzyl, respectively [47] ) even though S-14 and S-15 have two equivalent sites of attack whereas the three monoradicals have only one. Evidence that these values for S k A are indeed too low is given below, and rules out condition (3). What remains is condition (2), with the added requirement T k A /( T k 12 ϩ T k 13 ) ϽϽ S k A /( S k 12 ϩ S k 13 ) in order to raise S k A to appropriate values.…”

Section: Dimerisation Of 9 In the Presence Of Nitroxyls (R 2 No·) Pamentioning

confidence: 97%

“…The solid was treated with ether and the resulting ethereal solution was filtered and concentrated to 40 mL. At 6ar,6bc,12at,12bc-1,2,3,4,6a,6b,9,10,11,12,12a,12b-Dodecahydrocycloocta [3,4]…”

Section: Bis[2-(2-ethylhexyl)cyclohexane-11ј-dionato]copper(ii) (Cu)mentioning

confidence: 99%

“…[1] Singlet tetramethylene, which is the parent singlet 1,4-diradical (Scheme 1), has been prepared by a different route by pulse photolysis and has been shown to possess a lifetime of ca. 0.7 ps, [2,3] too long for a mere transition state. Hence, singlet 1,4-diradicals, if occurring in the course of [2ϩ2] cyclodimerisations, should be intermediates rather than transition states.…”

Section: Introductionmentioning

confidence: 99%

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The Thermal [2+2] Cyclodimerisation of (E,Z)-Cycloocta-1,3-diene Revisited − Chemical Trapping and Properties of the Intermediate 1,4-Diradicals

et al. 2002

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Keywords: Cycloaddition / Radicals / Reaction mechanisms / ThermochemistryThe thermal [2+2] cyclodimerisation of (E,Z)-cycloocta-1,3diene (9), which is known to afford the cyclobutane dimers 11, 12, and 13, has been investigated in the presence of the nitroxyls 17 and 18 and of atmospheric dioxygen, all of which are known to be efficient trapping agents for carbon-centred free radicals. The nitroxyls have been found to divert the reaction from formation of the dimers to formation of 2:2 adducts of two molecules of 9 and two molecules of nitroxyl. The rate constant for the formation of the overall sum of the dimers plus the 2:2 adducts in the presence of nitroxyl has been found to equal the rate constant for the formation of dimers in the absence of nitroxyl. This and the molecular structures of the 2:2 adducts prove that two molecules of 9 combine irreversibly to produce the two epimeric bis(allylic) 1,4-diradicals 14 and 15 (meso and rac, respectively) which undergo two competing reactions: ring-closure to dimers 11, 12, and 13, and trapping by nitroxyl to form the 2:2 adducts. Dioxygen, too, was found to trap 14 and 15 efficiently. From the kinetics of the latter trapping reaction, studied at six temperatures between 5 and 55°C, the heights of the activation barriers separating 14 from 11 and 15 from 12 + 13 were estimated at 11.1 ± 1.5 and 10.2 ± 1.5 kcal·mol −1 , respectively, corresponding to diradical lifetimes of ca. 0.5 µs. These unexpectedly high barriers have been verified by MM3 force-field calculations and by an investigation of the kinetics of the gas-phase thermolysis of 12 (to give 13 and 16 which is an epimer of 12 and 13) and of 13 (to give 12 and 16). When the [a]

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Section: Dimerisation Of 9 In the Presence Of Nitroxyls (R 2 No·) Pamentioning

confidence: 97%

Section: Bis[2-(2-ethylhexyl)cyclohexane-11ј-dionato]copper(ii) (Cu)mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The Thermal [2+2] Cyclodimerisation of (E,Z)-Cycloocta-1,3-diene Revisited − Chemical Trapping and Properties of the Intermediate 1,4-Diradicals

et al. 2002

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“…Note that the target of the present demonstration is just to show the capability of the method to track the reaction path on a given potential surface, regardless of the accuracy of the potential surface itself. There are a lot of work devoted to the research of cyclobutane, for example [24,25,26,27]. In work [24] the energy of dissociation was calculated by the composite method CBS-QB3 of quantum chemistry, and intrinsic reaction coordinate…”

Section: B)mentioning

confidence: 99%

AtomREM: Non-empirical seeker of the minimum energy escape paths on many-dimensional potential landscapes without coarse graining

Nagornov

Akashi

2020

Computer Physics Communications

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Recently a non-empirical stochastic walker algorithm has been developed to search for the minimum-energy escape paths (MEP) from the minima of the potential surface [J. Phys. Soc. Jpn. 87, 063801 (2018); Physica A, 528, 121481 (2019)]. This method is based on the Master equation for the distribution function of the atomic configuration which has a nature to seek the MEP up along the valley of the potential surface. This paper introduces AtomREM (Atomistic Rare Event Manager), which is an MPI parallelized solver program package for executing this method, which yields minimum energy reaction pathways in terms of the microscopic evolution of atomic positions. It is open-source and released under the GNU General Public License (GPL). AtomREM interfaces with the LAMMPS Molecular Dynamics Simulator as a library of versatile potential functions for application to various systems. Examples of the applications to molecular and solid systems are presented.

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“…Furthermore, applications of tailored UV pulses on small molecular systems cover a broad range of fundamental chemical reaction principles. Beginning with the cis/trans isomerization of stilbene [28,29] , over intramolecular proton transfer reactions in a salicylic acid derivate [30] or hydroxybenzaldehyde [31] to ring opening or formation reactions in 1,3-cyclohexadiene [32] or methylene diradicals [33] , UV pulses provide an universal ultrafast trigger for important chemical reaction mechanisms. On the other side, observation of biochemical relevant processes like the mutagenic dimerization of the DNA base thymine also requires the utilization of UV-pump pulses.…”

Section: Introductionmentioning

confidence: 99%

Quantum control spectroscopy (QCS) with a micro-electro-mechanical-system (MEMS)

2009

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Phase modulation of ultrashort UV pulses is developed for application in Quantum Control Spectroscopy (QCS) using a MEMS based two dimensional phase only modulator. The phase modulator consists of an array of 240 by 200 individually addressable, electrostatic displaceable micromirrors, placed in the Fourier plane of a purely reflective 4f-geometry. As possible applications, the adaptive recompression of ultrashort UV-pulses and arbitrary phase modulation for nonlinear spectroscopy and control experiments are discussed. Furthermore, the 2D layout of the device offers the potential to control multi beam experiments in a much easier way than with conventional experimental methods.

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Femtosecond dynamics of diradicals: transition states, entropic configurations and stereochemistry

Cited by 45 publications

References 31 publications

The Thermal [2+2] Cyclodimerisation of (E,Z)-Cycloocta-1,3-diene Revisited − Chemical Trapping and Properties of the Intermediate 1,4-Diradicals

The Thermal [2+2] Cyclodimerisation of (E,Z)-Cycloocta-1,3-diene Revisited − Chemical Trapping and Properties of the Intermediate 1,4-Diradicals

AtomREM: Non-empirical seeker of the minimum energy escape paths on many-dimensional potential landscapes without coarse graining

Quantum control spectroscopy (QCS) with a micro-electro-mechanical-system (MEMS)

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