- The Electron Spin Resonance Spectra of the Penta-alkylcyclopentadienyl Radicals MeR4C5 (R=Et, Pr, and Bu) and 1,3,5-Me3-2,4-Et2C5. Relative Substituent Effects of Alkyl Groups
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The penta-alkylcyclopentadienyl radicals Me4EtC5, Me4PrC5, Me4BuC5, and 1,3,5-Me3-2,4Et2C5 have been prepared by photolysis of the corresponding penta-alkylcyclopentadienes.The e.s.r. spectra which are observed are strongly temperature-dependent.It is assumed that the unsymmetrical penta-alkylation breaks the degeneracy of the ψA and ψS molecular orbitals of the cyclopentadienyl radical, and that there is a Boltzmann distribution of the unpaired electron between these two levels.The e.s.r. spectra which are observed then represent a population-weighted average of the spectra associated with the radical in the ψA1ψS2 and ψS2ψA1 configurations.The McLachlan equation is used to give the spin-density distribution in these two configurations, and the induced separation between the ψA and ψS energy levels can then be derived.It is concluded that in the ?-radical RC=, the relative electron-releasing interaction between the alkyl group R and a unit p-electron on the attached carbon atom falls in the sequence (kJ mol -1) Me(0) > Et(1.79) Pr(1.84) Bu(1.99).
- Davies, Alwyn G.,Goddard, Jeffrey P.,Lusztyk, Ewa,Lusztyk, Janusz
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p. 737 - 744
(2007/10/02)
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