Vibronic origin of the H3O metastability

Ogurtsov, I. Ya.; Gorinchoy, Natalia; Bălan, Iolanta

doi:10.1016/j.molstruc.2007.01.065

Cited by 10 publications

(6 citation statements)

References 9 publications

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“…[9][10][11][12][13][14][15][16] Whereas lower members of the cumulene carbenes have C 2v symmetry and 1 A 1 electronic ground states, [17][18][19] the situation for the closed-shell cumulenes is more complex. [20][21][22] Here, molecules having an even number of carbon atoms such as butatriene (H 2 C=C = C=CH 2 ) and hexapentaene (H 2 C=C = C= C = C=CH 2 ) belong to the D 2h point group (all four hydrogen atoms are in one symmetry plane); [23][24][25][26] on the other hand, cumulenes with an odd number of carbon atoms as found in propadiene/allene (H 2 C=C = CH 2 ) and pentatetraene (H 2 C=C = C=C = CH 2 ) dictate an inherent D 2d symmetry [27] and hence a pair-wise, staggered arrangement of the hydrogen atoms ( Figure 1, Table 1). This correlates with the 1 A g and 1 A 1 electronic ground states for the even-and odd-numbered cumulenes, respectively.…”

Section: Introductionmentioning

confidence: 99%

Chemistry of Energetically Activated Cumulenes—From Allene (H₂CCCH₂) to Hexapentaene (H₂CCCCCCH₂)

Kaiser

Mebel

2008

ChemPhysChem

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During the last decade, experimental and theoretical studies on the unimolecular decomposition of cumulenes (H(2)C(n)H(2)) from propadiene (H(2)CCCH(2)) to hexapentaene (H(2)CCCCCCH(2)) have received considerable attention due to the importance of these carbon-bearing molecules in combustion flames, chemical vapor deposition processes, atmospheric chemistry, and the chemistry of the interstellar medium. Cumulenes and their substituted counterparts also have significant technical potential as elements for molecular machines (nanomechanics), molecular wires (nano-electronics), nonlinear optics, and molecular sensors. In this review, we present a systematic overview of the stability, formation, and unimolecular decomposition of chemically, photo-chemically, and thermally activated small to medium-sized cumulenes in extreme environments. By concentrating on reactions under gas phase thermal conditions (pyrolysis) and on molecular beam experiments conducted under single-collision conditions (crossed beam and photodissociation studies), a comprehensive picture on the unimolecular decomposition dynamics of cumulenes transpires.

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Section: Introductionmentioning

confidence: 99%

Chemistry of Energetically Activated Cumulenes—From Allene (H₂CCCH₂) to Hexapentaene (H₂CCCCCCH₂)

Kaiser

Mebel

2008

ChemPhysChem

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“…Before elaborating on this phenomenon, we note that the trigonal-pyramidal structure of molecules isoelectronic with the sulfonium cation, the simplest being NH 3 , has long been discussed in terms of vibronic coupling and the pseudo-JT effect, , and likewise for the metastability of a radical somewhat analogous to R 3 S 0 , H 3 O 0 . However, in previous studies of the reductive cleavage reactions of sulfonium salts, − , it has not been recognized that the neutral R 3 S 0 radical exhibits a degenerate 2 E state and its behavior is vibronically driven.…”

Section: Analysis and Discussionmentioning

confidence: 96%

Active-Site Controlled, Jahn–Teller Enabled Regioselectivity in Reductive S–C Bond Cleavage of S-Adenosylmethionine in Radical SAM Enzymes

et al. 2020

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Catalysis by canonical radical S-adenosyl-l-methionine (SAM) enzymes involves electron transfer (ET) from [4Fe–4S]+ to SAM, generating an R3S0 radical that undergoes regioselective homolytic reductive cleavage of the S–C5′ bond to generate the 5′-dAdo· radical. However, cryogenic photoinduced S–C bond cleavage has regioselectively yielded either 5′-dAdo· or ·CH3, and indeed, each of the three SAM S–C bonds can be regioselectively cleaved in an RS enzyme. This diversity highlights a longstanding central question: what controls regioselective homolytic S–C bond cleavage upon SAM reduction? We here provide an unexpected answer, founded on our observation that photoinduced S–C bond cleavage in multiple canonical RS enzymes reveals two enzyme classes: in one, photolysis forms 5′-dAdo·, and in another it forms ·CH3. The identity of the cleaved S–C bond correlates with SAM ribose conformation but not with positioning and orientation of the sulfonium center relative to the [4Fe–4S] cluster. We have recognized the reduced-SAM R3S0 radical is a (2 E) state with its antibonding unpaired electron in an orbital doublet, which renders R3S0 Jahn–Teller (JT)-active and therefore subject to vibronically induced distortion. Active-site forces induce a JT distortion that localizes the odd electron in a single priority S–C antibond, which undergoes regioselective cleavage. In photolytic cleavage those forces act through control of the ribose conformation and are transmitted to the sulfur via the S–C5′ bond, but during catalysis thermally induced conformational changes that enable ET from a cluster iron generate dominant additional forces that specifically select S–C5′ for cleavage. This motion also can explain how 5′-dAdo· subsequently forms the organometallic intermediate Ω.

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“…It was proved analytically and confirmed by a series of numerical calculations [16][17][18][19][20] that, for any molecular system, K Γ 0Γ ≥ 0. This means that any structural instability and distortions of a high-symmetry configuration of any polyatomic system in a non-degenerate state is caused by and only by the vibronic coupling to appropriate excited states higher in energy.…”

Section: Vibronic Coupling Treatment Of High-symmetry Configuration Instabilitymentioning

confidence: 99%

Pseudo Jahn−Teller Origin of the Proton Tunneling in Zundel Cation Containing Water Clusters

2021

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The pseudo Jahn–Teller (PJT) origin of the proton transfer barrier in the Zundel cation at different O–O distances and in an H5O2+(H2O)4 cluster is revealed by means of ab initio calculations of their electronic structures and the adiabatic potential energy curves. The vibronic constants in this approach were estimated by fitting the ab initio calculated adiabatic potential to its analytical expression. It is shown also that the high-symmetry nuclear configurations ofproton-centered water clusters of the type H+(H2O)n (n = 6, 4, 3) are unstable with respect to the low-symmetry nuclear distortions leading to forming the dihydronium cation H5O2+ and the appropriate number of water molecules: H2n + 1On+ → (n – 2)H2O + H5O2+. The reason for this instability and the subsequent decay is the PJT coupling between the ground and excited electronic states.

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Vibronic origin of the H3O metastability

Cited by 10 publications

References 9 publications

Chemistry of Energetically Activated Cumulenes—From Allene (H₂CCCH₂) to Hexapentaene (H₂CCCCCCH₂)

Chemistry of Energetically Activated Cumulenes—From Allene (H₂CCCH₂) to Hexapentaene (H₂CCCCCCH₂)

Active-Site Controlled, Jahn–Teller Enabled Regioselectivity in Reductive S–C Bond Cleavage of S-Adenosylmethionine in Radical SAM Enzymes

Pseudo Jahn−Teller Origin of the Proton Tunneling in Zundel Cation Containing Water Clusters

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Vibronic origin of the H3O metastability

Cited by 10 publications

References 9 publications

Chemistry of Energetically Activated Cumulenes—From Allene (H2CCCH2) to Hexapentaene (H2CCCCCCH2)

Chemistry of Energetically Activated Cumulenes—From Allene (H2CCCH2) to Hexapentaene (H2CCCCCCH2)

Active-Site Controlled, Jahn–Teller Enabled Regioselectivity in Reductive S–C Bond Cleavage of S-Adenosylmethionine in Radical SAM Enzymes

Pseudo Jahn−Teller Origin of the Proton Tunneling in Zundel Cation Containing Water Clusters

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Chemistry of Energetically Activated Cumulenes—From Allene (H₂CCCH₂) to Hexapentaene (H₂CCCCCCH₂)

Chemistry of Energetically Activated Cumulenes—From Allene (H₂CCCH₂) to Hexapentaene (H₂CCCCCCH₂)