Experimental and Theoretical Studies of the Mechanism and Thermochemistry of Formation of .alpha.,n-Dehydrotoluene Biradicals from Gas-Phase Halide Elimination Reactions

Wenthold, Paul G.; Wierschke, Scott G.; Nash, John J.; Squires, Robert R.

doi:10.1021/ja00095a048

Cited by 85 publications

(113 citation statements)

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“…However, PO-UDFT predicts a singlet-triplet splitting of -0.5 and -1.0 kcal/mol, respectively, while both ROSS and ROKS calculations give erroneous singlet-triplet ordering as reflected by positive singlet-triplet splittings (0.8 and 0.9 kcal/mol, Table 2). Although these results seem to contradict the discussion in chapter 2, they become understandable in view of considerations (a) and (b): [32,45,55] that the 1 A" and 3 A" states of 2 show spin-polarization effects in the π-electron system, which require a multi-configuration description, i.e. strictly speaking 2 is a type III rather than a type I system.…”

Section: Description Of Open Shell Singlet Biradicals By Dft: Principmentioning

confidence: 68%

Can Unrestricted Density-Functional Theory Describe Open Shell Singlet Biradicals?

Gräfenstein

Kraka

Filatov

et al. 2002

IJMS

196

193

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Unrestricted density functional theory (UDFT) can be used for the description of open-shell singlet (OSS) biradicals provided a number of precautions are considered. Biradicals that require a two-determinantal wave function (e.g. OSS state of carbenes) cannot be described by UDFT for principal reasons. However, if the overlap between the open-shell orbitals is small (the single electrons are located at different atomic centers) errors become small and, then, the principal failure of UDFT in these cases is not apparent and may even be disguised by the fact that UDFT has the advantage of describing spin polarization better than any restricted open shell DFT method. In the case of OSS biradicals with two-or multiconfigurational character (but a onedeterminantal form of the leading configuration), reasonable results can be obtained by broken-symmetry (BS)-UDFT, however in each case this has to be checked. In no case is it reasonable to lower the symmetry of a molecule to get a suitable UDFT description. Hybrid functionals such as B3LYP perform better than pure DFT functionals in BS-UDFT calculations because the former reduce the self-interaction error of DFT exchange functionals, which mimics unspecified static electron correlation effects, so that the inclusion of specific static electron correlation effects via the form of the wavefunction becomes more effective.

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Section: Description Of Open Shell Singlet Biradicals By Dft: Principmentioning

confidence: 68%

Can Unrestricted Density-Functional Theory Describe Open Shell Singlet Biradicals?

Gräfenstein

Kraka

Filatov

et al. 2002

IJMS

196

193

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“…In 1994, Squires et al [2] reported on a determination of the heat of formation of α,2-dehydrotoluene by the CID method. However, the experimental value did not agree well with that calculated by ab initio methods.…”

Section: Introductionmentioning

confidence: 99%

“…The heat of formation of the triplet state, however, is only an upper limit, which gives the singlet-triplet splitting as Ͼ 6 kcal⋅mol Ϫ1 . For the parent system, Squires [2] calculated a value of 7.4 kcal⋅mol Ϫ1 .…”

Section: Introductionmentioning

confidence: 99%

Thermochemistry of 7,7-Difluoro-2,7-toluenediyl

Roth¹,

Figge²

2000

Eur. J. Org. Chem.

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From the oxygen and temperature dependence of the trapping rate of 7,7‐difluorobenzocyclopropene (1) in the range 180−240 °C, the energy profile of the equilibrium 1 →←2 has been obtained. From the heat of hydrogenation of 1, its heat of formation is derived (ΔH of = +3.8 kcal·mol−1), as a result of which the heat of formation of the singlet state of the diradical 2 is estimated as 25.7 kcal·mol−1. Whereas the trapping experiments demonstrate unambiguously a triplet ground state for 2, only a lower limit for the singlet‐triplet splitting (> 6 kcal·mol−1) can be given.

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“…The MX biradical has a triplet ground state [2][3][4] with two ferromagnetically coupled electrons in two p molecular orbitals ( Figure 1). DHT, also shown in Figure 1, is a s 1 p 1 biradical [5] with singlet-coupled unpaired electrons, a result of spin polarization that favors antiferromagnetic coupling. [5,6] The features responsible for the MX and DHT ground state multiplicities are also present in DMX.…”

mentioning

confidence: 98%

“…DHT, also shown in Figure 1, is a s 1 p 1 biradical [5] with singlet-coupled unpaired electrons, a result of spin polarization that favors antiferromagnetic coupling. [5,6] The features responsible for the MX and DHT ground state multiplicities are also present in DMX. The p system is similar to that of MX, such that it should contain two ferromagnetically coupled electrons.…”

mentioning

confidence: 98%

5‐Dehydro‐1,3‐quinodimethane: A Hydrocarbon with an Open‐Shell Doublet Ground State

Slipchenko¹,

Munsch²,

Wenthold³

et al. 2004

Angewandte Chemie

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Experimental and Theoretical Studies of the Mechanism and Thermochemistry of Formation of .alpha.,n-Dehydrotoluene Biradicals from Gas-Phase Halide Elimination Reactions

Cited by 85 publications

References 0 publications

Can Unrestricted Density-Functional Theory Describe Open Shell Singlet Biradicals?

Can Unrestricted Density-Functional Theory Describe Open Shell Singlet Biradicals?

Thermochemistry of 7,7-Difluoro-2,7-toluenediyl

5‐Dehydro‐1,3‐quinodimethane: A Hydrocarbon with an Open‐Shell Doublet Ground State

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