Heteroatomic substitution in aromatic σ biradicals: the six pyridynes

Cramer, Christopher J.; Debbert, Stefan L.

doi:10.1016/s0009-2614(98)00192-4

Cited by 75 publications

(126 citation statements)

References 20 publications

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“…As noted recently, many theoretical studies [7,19,20,27,28,36,52,53] have made efforts to compute the S-T splitting (DE T-S ) for 1P (the p-benzyne biradical), and Cramer [19] predicted the DE T-S values not only for 1P but also for 2P (single N-substituted ring biradical) by using various theoretical methods such as BPW91, CASPT2//BPW91, CCSD(T)//BPW91, and BCCD(T)// BPW91. In Table 4 listed are our CASPT2 adiabatic DE T-S values with the CASSCF ZPVE-corrections for the reactants and products in reactions 1-5, together with the available experimental and precious theoretical values.…”

Section: Full Paper Wwwc-chemorgmentioning

confidence: 88%

“…Halter et al [1] performed the geometry optimization calculations for 2R and 4R in their ground states (the S 0 states) using CCSD(T)/cc-pVTZ method and the optimized geometries are in agreement with experiment. For the Bergman cyclizations of 2R and 3R (reactions 2 and 3 in Scheme 1), there are a few theoretical studies [1,7,19,22,[36][37][38] reported in the literature. Hoffner et al [22] studied these two reactions along the S 0 potential energy surfaces (PESs) by performing the CASSCF(6,6)/6-31G* and CASMP2(6,6)/6-31G* single-point energy calculations at the CASSCF(6,6)/3-21G geometries and predicted the energy barriers, the reaction enthalpies, and the singlet-triplet splitting for the biradical products.…”

Section: Introductionmentioning

confidence: 99%

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The bergman cyclizations of the enediyne and its N‐substituted analogs using multiconfigurational second‐order perturbation theory

et al. 2011

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The Bergman cyclizations of the enediyne and its four N-substituted analogs [(Z)-pent-2-en-4-ynenitrile, 3-azahex-3-en-1,5-diyne, malenotrile, and 3,4-azahex-3-en-1,5-diyne] have been studied using the complete active space self-consistent field and multiconfigurational second-order perturbation theory methods in conjunction with the atomic natural orbital basis sets. The geometries and energies of the reactants, transition states, and products along both the S(0) (the ground state) and T(1) (the lowest-lying triplet state) potential energy surfaces (PESs) were calculated. The calculated geometries are in good agreement with the available experimental data. The distance between two terminal carbons in enediyne, which was considered as an important parameter governing the Bergman cyclization, was predicted to be 4.319 Å, in agreement with the experimental value of 4.321 Å. Our calculations indicate that the replacements of the terminal C atom(s) or the middle C atom(s) in the C=C bond by the N atom(s) increase or decrease the energy barrier values, respectively. There exist stable ring biradical products on the T(1) PESs for the five reactions. However, on the S(0) PESs the ring biradical products exist only for the reactions of enediyne, (Z)-pent-2-en-4-ynenitrile, and 3-azahex-3-en-1,5-diyne.

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Section: Full Paper Wwwc-chemorgmentioning

confidence: 88%

Section: Introductionmentioning

confidence: 99%

The bergman cyclizations of the enediyne and its N‐substituted analogs using multiconfigurational second‐order perturbation theory

et al. 2011

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“…Thus, it has been shown previously that CASPT2/ cc-pVDZ S-T splittings in aryne diradicals are well correlated with BPW91/cc-pVDZ monoradical 1 H hfs constants, 8,36,57 where the hfs is computed for the hydrogen atom on the diradical position that is "capped" in the monoradical (while a separate correlation with experiment would be expected to be of similarly high quality, experimental data are, for the most part, not available for such an undertaking). For strongly interacting ortho-and meta-related diradicals (defined as having singlet ground states with S-T gaps larger in magnitude than -10 kcal/ mol), the regression equation, which has an R value of 0.997 when computed over 11 data points for relevant benzynes, 36 pyridynes, 56 and naphthalynes, 8,36 is…”

Section: Resultsmentioning

confidence: 99%

“…Considerable fluxionality in m-benzyne and analogous systems has been noted many times previously; in various instances theoretically characterized coordinates ranging from monocyclic to bicyclic structures have been found to be quite flat. 27,32,35,37,48,56,57 A general rule of thumb seems to be that BPW91 structures are too far displaced toward being bicyclic, while CAS structures tend to be too far displaced toward being monocyclic. The DDIs show trends consistent with this observation.…”

Section: Discussionmentioning

confidence: 99%

Quantum Chemical Characterization of Singlet and Triplet Didehydroindenes

Cramer¹,

Thompson

2001

J. Phys. Chem. A

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Structural and energetic properties for the lowest energy singlet and triplet states of the 19 possible didehydroindene isomers are predicted using coupled cluster, density functional, and multireference secondorder perturbation theories. Singlet-triplet splittings and biradical stabilization energies provide a measure of the degree of interaction between the biradical centers. Comparisons to analogous didehydronaphthalenes are made to understand the influence of the five-membered ring. As in other didehydroarenes, proton hyperfine splittings in antecedent monoradicals are economical predictors of biradical state energy splittings.

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“…According to Cramer and Debbert, meta-benzyne analogs can be represented by a zwitterionic resonance structure, which consists of a cyclopropenium cation and an allyl anion (Scheme 1) [18]. The stability of the zwitterionic resonance structure influences the separation (distance) between the two radical sites [hereafter referred to as the Bdehydrocarbon atom separation^(DAS)].…”

Section: Introductionmentioning

confidence: 99%

Gas-phase Reactivity of meta-Benzyne Analogs Toward Small Oligonucleotides of Differing Lengths

Widjaja

Max

Jin

et al. 2017

J. Am. Soc. Mass Spectrom.

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Abstract. The gas-phase reactivity of two aromatic carbon-centered σ,σ-biradicals (meta-benzyne analogs) and a related monoradical towards small oligonucleotides of differing lengths was investigated in a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer coupled with laser-induced acoustic desorption (LIAD). The mono-and biradicals were positively charged to allow for manipulation in the mass spectrometer. The oligonucleotides were evaporated into the gas phase as intact neutral molecules by using LIAD. One of the biradicals was found to be unreactive. The reactive biradical reacts with dinucleoside phosphates and trinucleoside diphosphates mainly by addition to a nucleobase moiety followed by cleavage of the glycosidic bond, leading to a nucleobase radical (e.g., base-H) abstraction. In some instances, after the initial cleavage, the unquenched radical site of the biradical abstracts a hydrogen atom from the neutral fragment, which results in a net nucleobase abstraction. In sharp contrast, the related monoradical mainly undergoes facile hydrogen atom abstraction from the sugar moiety. As the size of the oligonucleotides increases, the rate of hydrogen atom abstraction from the sugar moiety by the monoradical was found to increase due to the presence of more hydrogen atom donor sites, and it is the only reaction observed for tetranucleoside triphosphates. Hence, the monoradical only attacks sugar moieties in these substrates. The biradical also shows significant attack at the sugar moiety for tetranucleoside triphosphates. This drastic change in reactivity indicates that the size of the oligonucleotides plays a key role in the outcome of these reactions. This finding is attributed to more compact conformations in the gas phase for the tetranucleoside triphosphates than for the smaller oligonucleotides, which result from stronger stabilizing interactions between the nucleobases.

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Heteroatomic substitution in aromatic σ biradicals: the six pyridynes

Cited by 75 publications

References 20 publications

The bergman cyclizations of the enediyne and its N‐substituted analogs using multiconfigurational second‐order perturbation theory

The bergman cyclizations of the enediyne and its N‐substituted analogs using multiconfigurational second‐order perturbation theory

Quantum Chemical Characterization of Singlet and Triplet Didehydroindenes

Gas-phase Reactivity of meta-Benzyne Analogs Toward Small Oligonucleotides of Differing Lengths

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