New Approach to Carbene Chemistry <i>via</i> Distonic Carbene Ions. A Case of Spin-Forbidden Proton Transfer and Carbene−Biradical Tautomerism

Hu, Jun; Hill, Brian T.; Squires, Robert R.

doi:10.1021/ja9727070

Cited by 26 publications

(19 citation statements)

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“…Although this concept represents only one aspect of chemical reactivity, it has proven to be a useful tool in rationalizing the greater part of reactions. [3] They synthesized a so-called distonic [4] carbene ion, that is, a species where the charged and the carbenic moieties are formally separate, in a flowing afterglow-triple-quadrupole apparatus by the reaction sequence shown in Scheme 1. Nevertheless, the simple example of the stability of many organic compounds with regard to ground-state triplet O 2 should always remind us of the important consequences of spin states on reactivity.…”

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confidence: 99%

“…[3] They synthesized a so-called distonic [4] carbene ion, that is, a species where the charged and the carbenic moieties are formally separate, in a flowing afterglow-triple-quadrupole apparatus by the reaction sequence shown in Scheme 1. [3] They synthesized a so-called distonic [4] carbene ion, that is, a species where the charged and the carbenic moieties are formally separate, in a flowing afterglow-triple-quadrupole apparatus by the reaction sequence shown in Scheme 1.…”

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confidence: 99%

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Interspin Crossing and Reactivity

Plattner

1999

Angew. Chem. Int. Ed.

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The discussion of reaction mechanisms and pathways is usually based on a single potential energy surface: starting from the reactant minimum the reactive system moves through a transition state and proceeds further to intermediates and/or product minima. Although this concept represents only one aspect of chemical reactivity, it has proven to be a useful tool in rationalizing the greater part of reactions. The success of this concept and its justification, especially in organic chemistry, lies in the fact that organic species generally possess low-spin ground states, and their reactions proceed on a single energy surface (single-state reactivity). Nevertheless, the simple example of the stability of many organic compounds with regard to ground-state triplet O 2 should always remind us of the important consequences of spin states on reactivity. Reactions that involve a change in the spin state and thus occur on two or more potential energy surfaces (and are therefore nonadiabatic processes [1] ) have received much attention in recent years. A number of reactions in organic, inorganic, and organometallic chemistry, in which two states of different multiplicities determine the minimum-energy reaction pathway (two-state reactivity), have been confirmed by experimental and computational studies, and it is the aim of the present article to highlight those efforts.Gas-phase ion chemistry provides a powerful tool for the study of intermediates that are too reactive for a solutionphase characterization. Moreover, information about the intrinsic reactivity of the molecule or reactive system in question is obtained in the gas phase, unperturbed by effects of solvents or aggregation phenomena. Recently, two experimental gas-phase studies have confirmed the possibility of a spin-forbidden proton-transfer reaction, that is, a protonation during which a spin change occurs. The first reaction under consideration is the protonation of F À by HNO [Eq. (a)] [2] ).The energetics of the ground-state reaction, that is, the reaction with 1 HNO, are known from the heats of formation of the ions and molecules (Figure 1). The reaction is exothermic by 8 kcal mol À1 and leads to 3 (NO À ), since 1 (NO À ) is not a bound state. In the study of Brauman and co-workers, the nature of the intermediate complex [FHNO] À and its reactivity were addressed. [FHNO] À was synthesized by the reaction of F À with neopentyl nitrite and then treated with a variety of neutral molecules. The reaction products F -+ 3 (HNO) F -+ 1 (HNO) FH • 3 (NO -) F -• 1 (HNO) HF + 3 (NO -) HF + 1 (NO -) 18 33 18 25 8 Figure 1. Schematic potential energy diagram for reaction (a). The relative energies are given in kcal mol À1 .were monitored in a Fourier transform mass spectrometer. Reactions with alcohols and HCN give F À transfer, which indicates the structure of the complex is F À´H NO. On the other hand, reaction with NO gives N 2 O 2 , and the reactions with SF 6 , O 2 , and SO 2 lead to electron and/or HF transfer as would be expected for the triplet FH´3(NO) À . Thi...

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confidence: 99%

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confidence: 99%

Interspin Crossing and Reactivity

Plattner

1999

Angew. Chem. Int. Ed.

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“…[3] Sie synthetisierten ein ¹distonischesª [4] Carben-Ion, d. h. ein Molekül, bei dem die ladungstragende und die Carben-Einheit nicht in Konjugation stehen, in einem Flowing-afterglow-Tripel-Quadrupol-Aufbau durch die in Schema 1 gezeigte Reaktionskaskade. [3] Sie synthetisierten ein ¹distonischesª [4] Carben-Ion, d. h. ein Molekül, bei dem die ladungstragende und die Carben-Einheit nicht in Konjugation stehen, in einem Flowing-afterglow-Tripel-Quadrupol-Aufbau durch die in Schema 1 gezeigte Reaktionskaskade.…”

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Spinumkehr und Reaktivität

Plattner

1999

Angewandte Chemie

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“…Moreover, this carbene is a ground state triplet with a relatively large S-T gap of 9.00 ± 0.09 kcal mol −1 [20], which should enable the two possibilities (singlet versus triplet formation) to be differentiated since all of the relevant thermochemistry is well-established. In this work, we show that the deprotonation of CH 3 + is a rare example of a spin forbidden reaction [21][22][23], and the heat of formation of CHCl and CCl 2 are redetermined.…”

Section: Introductionmentioning

confidence: 77%

“…Since the ions and bases are all singlets, the formation of triplet methylene means that these acid-base reactions are a rare example of a spin-forbidden process [21][22][23]. There also appears to be no significant bottleneck near the threshold in these transformations since diethyl ether reacts at approximately the collision limit even though proton transfer is only exothermic by 1 kcal mol −1 .…”

Section: Methyl Cationmentioning

confidence: 99%