A Perspective on Physical Organic Chemistry

Platz, Matthew S.

doi:10.1021/jo500044d

Cited by 25 publications

(32 citation statements)

References 70 publications

(174 reference statements)

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“…The combination of ultrafast transient vibrational absorption spectroscopy (TVAS) and TEAS is powerful for investigation of bimolecular radical-reaction mechanisms because the formation and decay of the initial radical can be monitored by TEAS, with subsequent reaction intermediates observed by TVAS. [19][20][21] Here, we demonstrate that TVAS at discrete time delays from 200 fs to 50 s in a single set of measurements, combined with TEAS over a more restricted time range from 100 fs -1.3 ns, provides a comprehensive view of a sequence of unimolecular initiation and bimolecular addition steps in a radical chain reaction.…”

Section: Introductionmentioning

confidence: 71%

Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

Koyama

Donaldson

Orr-Ewing

2017

Phys. Chem. Chem. Phys.

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Section: Introductionmentioning

confidence: 71%

Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

Koyama

Donaldson

Orr-Ewing

2017

Phys. Chem. Chem. Phys.

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“…Importantly, these intermolecular interactions can modulate the lifetime, intersystem crossing, and reactivity rates of carbenes. 19−21 It has frequently been observed that polar solvents selectively stabilize the singlet state. 14,17 In the case of triplet ground-state carbenes, complexation with highly polar compounds can render the singlet state sufficiently accessible to participate in a reaction, or may even invert the singlet–triplet gap ( E S–T ), resulting in a singlet ground state.…”

Section: Introductionmentioning

confidence: 99%

Physical Nature of Differential Spin-State Stabilization of Carbenes by Hydrogen and Halogen Bonding: A Domain-Based Pair Natural Orbital Coupled Cluster Study

et al. 2019

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The variation in the singlet–triplet energy gap of diphenylcarbene (DPC) upon interaction with hydrogen (water and methanol) or halogen bond (XCF 3 , X = Cl, Br, I) donors to form van der Waals (vdW) complexes is investigated in relation to the electrostatic and dispersion components of such intermolecular interactions. The domain-based local pair natural orbital coupled cluster method, DLPNO–CCSD(T), is used for calculating accurate single–triplet energy gaps and interaction energies for both spin states. The local energy decomposition scheme is used to provide an accurate quantification to the various interaction energy components at the DLPNO–CCSD(T) level. It is shown that the formation of vdW adducts stabilizes the singlet state of DPC, and in the case of water, methanol, and ICF 3 , it reverses the ground state from triplet to singlet. Electrostatic interactions are significant in both spin states, but preferentially stabilize the singlet state. For methanol and ClCF 3 , London dispersion forces have the opposite effect, stabilizing preferentially the triplet state. The quantification of the energetic components of the interactions through the local energy decomposition analysis correlates well with experimental findings and provides the basis for more elaborate treatments of microsolvation in carbenes.

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“…17,18 They yield carbenes photochemically under mild conditions. 19,20 Ultrafast time-resolved laser flash photolysis of aryl diazo compounds [21][22][23] and aryldiazirines [24][25][26] has provided valuable information on the dynamics of the precursor excited states and the generated singlet arylcarbenes. Using ultrafast infrared spectroscopy, the singlet aryldiazomethane and arylcarbene intermediates were detected in the photolysis of phenyldiazirine, phenylchlorodiazirine and p-methoxy-3-phenyl-3-methyldiazirine in less than 1 ps upon excitation.…”

Section: Introductionmentioning

confidence: 99%

Theoretical study of non-Hammettvs.Hammett behaviour in the thermolysis and photolysis of arylchlorodiazirines

Peng

Migani

et al. 2018

Phys. Chem. Chem. Phys.

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Arylchlorodiazirines (ACDA) are thermal and photochemical precursors of carbenes that form these molecules via nitrogen elimination. We have studied this reaction with multireference quantum chemical methods (CASSCF and CASPT2) for a series of ACDA derivatives with different substitution at the aromatic ring. The calculations explain the different reactivity trends found in the ground and excited state, with good correlation between the calculated barriers and the experimental reaction rates. The ground state mechanism can be described as a reverse cycloaddition with small charge transfer from the aromatic ring to the diazirine moiety. This is consistent with the lack of correlation between the Hammett σ descriptors and the experimental rates. In contrast, the excited state reaction is the cleavage of a single C-N bond mediated by small barriers of 4-6 kcal mol. The reaction path goes through a conical intersection with the ground state, which facilitates radiationless decay and explains the disappearance of the transient absorption signal measured experimentally. This leads to a diazomethane intermediate that ultimately yields the carbene. Electronically, excitation to S is characterized initially by significant charge transfer from the phenyl ring to the diazirine. The charge transfer is reversed during the C-N cleavage reaction, and this explains the preferential stabilization of the excited-state minimum by polar solvents and electron-donating substituents. Therefore, our calculations reproduce and explain the relationship found experimentally between the Hammett σ parameters and the life time of S (Y. L. Zhang, et al. J. Am. Chem. Soc., 2009, 131, 16652-16653).

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A Perspective on Physical Organic Chemistry

Abstract: A perspective on the development of mechanistic carbene chemistry is presented. The author will point out questions that have been answered, and a next generation of questions will be proposed.

Cited by 25 publications

References 70 publications

Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

Femtosecond to microsecond observation of the photochemical reaction of 1,2-di(quinolin-2-yl)disulfide with methyl methacrylate

Physical Nature of Differential Spin-State Stabilization of Carbenes by Hydrogen and Halogen Bonding: A Domain-Based Pair Natural Orbital Coupled Cluster Study

Theoretical study of non-Hammettvs.Hammett behaviour in the thermolysis and photolysis of arylchlorodiazirines

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