Visualizing Carbene Equilibria

Moss, Robert A.; Wang, Lei; Hoijemberg, Pablo A.; Krogh‐Jespersen, Karsten

doi:10.1111/php.12120

Cited by 4 publications

(5 citation statements)

References 32 publications

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“…These experimental observations were found to be consistent with the results of theoretical calculations Remarkably, although time-resolved laser flash photolysis (LFP) has played a critical role in studying various types of carbenes, − there appear to be no reports attesting to the use of this method for the investigation of alkylidenecarbenes. Perhaps this conspicuous void in the literature may be attributed to the lack of photochemical precursors suitable for such studies.…”

Section: Introductionsupporting

confidence: 65%

Direct Observation of an Alkylidenecarbene by Ultrafast Transient Absorption Spectroscopy

Lan

Phillips

et al. 2018

J. Phys. Chem. A

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Singlet α-methylbenzylidenecarbene has been detected and characterized for the first time by femtosecond transient absorption (fs-TA) spectroscopy. The carbene was generated by photolysis of the hydrocarbon precursor, 1-(1-phenylethylidene)-1a,9b-dihydro-1 H-cyclopropa[ l]-phenanthrene, in acetonitrile. The photolysis initially forms the singlet excited state of the precursor which then extrudes α-methylbenzylidenecarbene in 4.0 ps. The decay of α-methylbenzylidenecarbene, which was previously shown to rearrange into phenylpropyne by a 1,2-phenyl shift, occurred over 13.3 ps. Computed spectra at the TD-B3LYP/6-311+G** level of theory are consistent with the experimental observations. CASSCF(10,10)/6-311+G** calculations, using one of the carbene conformers as a model, indicated that the reference wave function is dominated by a closed-shell description.

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Section: Introductionsupporting

confidence: 65%

Direct Observation of an Alkylidenecarbene by Ultrafast Transient Absorption Spectroscopy

Lan

Phillips

et al. 2018

J. Phys. Chem. A

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“…Recent studies have shown that once generated, ground state singlet carbenes can be temporarily stabilized by means of the formation of meta-stable complexes with solvent molecules having nonbonding electrons (examples: oxygen atoms in ethers or alcohols) or p electrons (examples: benzene, aromatic rings). [11][12][13] The stabilization would occur through the interaction between the excess electron density in solvent molecules and the empty p-like orbital in the carbene carbon atom. 14 Singlet carbenes can be generated from photolysis of diazirines 15,16 using laser flash photolysis (LFP).…”

Section: Introductionmentioning

confidence: 99%

Theoretical tools to distinguish O-ylides from O-ylidic complexes in carbene–solvent interactions

Gómez

Restrepo

Hadad

2015

Phys. Chem. Chem. Phys.

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In this paper, we report the geometries and properties of 48 molecular species located on the MP2/6-311++G(d,p) PES of the fluorocarbene-(methanol)3 system. The structures were found by a combination of a stochastic search method, using a modified Metropolis acceptance test, and some hand constructed very symmetrical structures. We use several theoretical descriptors to categorize these species, focusing our attention on the interaction between the carbene carbon and the methanol oxygen, CcO, because this is the key interaction in the formation of O-ylides, ether products, and O-ylidic solvation complexes. These descriptors include natural charges and natural bond orbitals (NBO), CcO bond orders, CcO distances, energetic stabilities, and properties at bond critical points. Accordingly, the isomers were divided into four groups: ethers, fluorocarbene-methanol O-ylides, O-ylidic carbene-solvent complexes and hydrogen bonded carbene-solvent complexes. We found that the possibility of forming H-bonds among solvent molecules and between the carbene carbon and the hydrogen of the solvent molecule affects the stability, structure and nature of CcO interactions in O-ylides and O-ylidic complexes to the point of generating some diffuse borderlines between these two kinds of species. We determined which set of theoretical tools is suitable to better distinguish between them. Additionally, we clarify the nature of the relevant interactions in these species.

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“…LFP of dichlorodiazirine in 1:1 MeCN−CH 2 Cl 2 solution containing 0.9 M TBACl affords a weak absorbance for CCl 3 − at 328 nm in accord with the reverse of eq 8. 53,54 Unfortunately, the equilibrium constant (K) could not be determined because the absorbance of CCl 2 in the solution is too weak under our LFP conditions. An indirect determination of K ∼ 10 M −1 is possible for the equilibrium of eq 9 involving CCl 2 Br − (388 nm).…”

Section: Diazirine-exchange Reaction and Derived Carbenesmentioning

confidence: 99%

Adventures in Reactive Intermediate Chemistry: A Perspective and Retrospective

Moss

2017

J. Org. Chem.

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I review aspects of my research on reactive intermediates, specifically the physical organic chemistry of carbenes and carbocations. The topics treated include carbenoids, carbenic philicity, absolute rates of carbene/alkene additions, the diazirine exchange reaction and derived carbenes, carbene equilibria, carbocations from diazotates, and carbocations from alkoxychlorocarbenes. The essay concludes with observations on the protean nature of physical organic chemistry.

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Visualizing Carbene Equilibria

Cited by 4 publications

References 32 publications

Direct Observation of an Alkylidenecarbene by Ultrafast Transient Absorption Spectroscopy

Direct Observation of an Alkylidenecarbene by Ultrafast Transient Absorption Spectroscopy

Theoretical tools to distinguish O-ylides from O-ylidic complexes in carbene–solvent interactions

Adventures in Reactive Intermediate Chemistry: A Perspective and Retrospective

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