Direct observation of the ylides formed upon reaction of cyclopentadienylidene with acetic anhydride, dimethyl carbonate, ethyl acetate and acetone

Platz, Matthew S.; Olson, David R.

doi:10.1002/(sici)1099-1395(199610)9:10<689::aid-poc823>3.0.co;2-w

Cited by 12 publications

(9 citation statements)

References 34 publications

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“…Carbenes are known to add to carbonyl groups of ketones and aldehydes. 25,26,38 Had this mode of reaction occurred in polymers with ester groups of VAc units, an additional attachment product, perhaps with different fluorescence decay constants, should have been observed. A search of the literature reveals that addition to carbonyl groups of ester substrates can be induced only under conditions different from those employed here and with specific reagents unlike those employed here: 26,31,38 strongly electrophilic carbenes react rapidly with ester groups; addition to the acetate group has not been observed although there have been attempts to induce such a process.…”

Section: Reaction Mechanism and Selectivity Of Attachmentmentioning

confidence: 99%

“…A search of the literature reveals that addition to carbonyl groups of ester substrates can be induced only under conditions different from those employed here and with specific reagents unlike those employed here: 26,31,38 strongly electrophilic carbenes react rapidly with ester groups; addition to the acetate group has not been observed although there have been attempts to induce such a process. 25,26,34,38 Based on these data, the most probable attachment modes involve insertion of pyren-1-ylcarbene into C-H bonds of the polymer chains or pendant groups (Fig. 2), even when there are abundant opportunities for addition to carboxy functionalities.…”

Section: Reaction Mechanism and Selectivity Of Attachmentmentioning

confidence: 99%

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Selective attachment of pyrenyl groups to ethylene-co-vinyl acetate copolymers: dynamic and static fluorescence studies

Yamaki

Atvars

Weiss

2002

Photochem Photobiol Sci

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Micromorphology is an important factor in determining polymer properties and uses. Here, steady-state and dynamic fluorescence from covalently attached 1-alkylpyrenyl groups are used to investigate the micromorphology of several random ethylene-co-vinyl acetate (EVA) copolymers with defined compositions of vinyl acetate monomer. The results are compared with those from homopolymers of high- and low-density polyethylenes and poly(vinyl acetate). Selective attachment of pyren-1-yl groups to polymer chains was accomplished by irradiation of pyren-1-yldiazomethane sorbed into polymer films. Steady-state fluorescence spectra and fluorescence decay rates of attached pyrenyl groups in films of the polymers have been compared with those from films with sorbed pyrene. I1/I3 intensity ratios from vibrational bands in the fluorescence spectra and the fluorescence decay rates of attached 1-alkylpyrenyl groups are much less sensitive to changes in the copolymer composition than are those of pyrene. These observations suggest that attachment occurs selectively to the olefinic segments (rather than to the acetate-rich regions) of polymer chains of EVA copolymers. This conclusion is consistent with the known preferences for reaction by pyren-1-ylcarbene in solution.

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Section: Reaction Mechanism and Selectivity Of Attachmentmentioning

confidence: 99%

Section: Reaction Mechanism and Selectivity Of Attachmentmentioning

confidence: 99%

Selective attachment of pyrenyl groups to ethylene-co-vinyl acetate copolymers: dynamic and static fluorescence studies

Yamaki

Atvars

Weiss

2002

Photochem Photobiol Sci

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“…“Saturated” electrophilic singlet carbenes ( 1 ), endowed with an empty p-orbital on the formally sp 2 -hybridized divalent and neutral carbon atom, are known to accept an electron pair from heteroatom-containing moieties (e.g., 2 ) to form the corresponding ylides ( 3 ) (Scheme ). − These carbene-derived ylides have proven to be of considerable synthesis value, − and in many instances, they have been directly observed and spectroscopically characterized. − The structurally different “unsaturated” alkylidenecarbenes ( 4 ), which feature an sp-hybridized carbon atom attached to only one substituent by a double bond, prefer singlet ground states and are electrophilic in nature (Scheme ). − As expected, carbenes such as 4 also form ylides 5 by accepting an electron pair in their vacant p-orbital from appropriate nucleophilic donors ( 2 ) (Scheme ).…”

Section: Introductionmentioning

confidence: 99%

Detection of Ylide Formation between an Alkylidenecarbene and Acetonitrile by Femtosecond Transient Absorption Spectroscopy

Sarkar

Bai

et al. 2021

J. Am. Chem. Soc.

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Femtosecond laser flash photolysis of 3-(1a,9b-dihydro-1H-cyclopropa[l]phenanthren-1-ylidene)tetrahydrofuran produces singlet 3-oxacyclopentylidenecarbene which reacts with acetonitrile solvent to form an ylide. This is the first direct detection of ylide formation by an alkylidenecarbene. This new type of ylide was observed to have a broad absorption band in the visible region with λ max ∼450 nm and a lifetime of ∼13.5 ps. As with other "conventional" carbenes (the divalent carbon atom is separately bound to two substituents), this ylide formation method could be also useful for detecting alkylidenecarbenes, especially those that do not absorb at wavelengths suitable for direct observation. Furthermore, the mechanisms by which 3-oxacyclopentylidenecarbene forms the ylide and the overall favorability of ylide formation, vis-a-vis ring expansion of the carbene to strained 3-oxacyclohexyne, were supported by results from density functional theory calculations.

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“…These facts could explain why in some situations, as in reactions of arylchlorocarbenes with esters, the detection of the respective ylide failed to be accomplished, while the same carbene forms an ylide with acetone . Only the most reactive arylchlorocarbenes were observed to form ylides with esters, or when an aromatic structure can result …”

Section: Introductionmentioning

confidence: 99%

A New Mechanism for the Reaction of Carbenes with OH Groups

Pliego

Almeida

1999

J. Phys. Chem. A

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The reaction pathway for the 2H2O + CCl2 reaction through a cyclic five-atom transition structure was studied using ab initio molecular orbital theory. The MP2 method in conjunction with the DZP basis set was used for geometry optimizations, and single point energy calculations were performed at MP2 and MP4 levels with the cc-pVDZ and cc-pVTZ basis sets. The solvent effect on the activation free energy was evaluated by Monte Carlo statistical mechanics calculations. The new mechanism has a high rate constant, and we predict a lifetime of seven nanoseconds for dichlorocarbene in aqueous solution. We have proposed that this mechanism occurs for the reaction of dichlorocarbene with water, and possibly may be involved in many reactions of carbenes with alcohols. We have also shown that it can explain the following experimental facts: (a) alteration of the product isotopic effect on addition of a second alcohol, (b) difference between product and kinetic isotopic effects, and (c) no linear dependence of the observed rate constant for carbene decay on alcohol concentration.

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Direct observation of the ylides formed upon reaction of cyclopentadienylidene with acetic anhydride, dimethyl carbonate, ethyl acetate and acetone

Cited by 12 publications

References 34 publications

Selective attachment of pyrenyl groups to ethylene-co-vinyl acetate copolymers: dynamic and static fluorescence studies

Selective attachment of pyrenyl groups to ethylene-co-vinyl acetate copolymers: dynamic and static fluorescence studies

Detection of Ylide Formation between an Alkylidenecarbene and Acetonitrile by Femtosecond Transient Absorption Spectroscopy

A New Mechanism for the Reaction of Carbenes with OH Groups

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