Jahn-Teller cyclopropane radical cation

The cyclopropane radical cation can be prepared by y-radiolysis in rigid matrices. At temperatures as low as 4.2 K, its ESR spectrum shows evidence for static Jahn-Teller distortion, resulting in a structure of the (ring-closed) trimethylene ( Ai) type, r " ... 

The cyclopropane radical cation can be prepared by y-radiolysis in rigid matrices its ESR spectrum at 4.2 K shows evidence for static Jahn-Teller distortion, resulting in a structure of the trimethylene (2Aj) type [294, 295], Irradiation of several methyl substituted derivatives at 77 K gave rise to a family of radical cations of the same structure type [293], which had been previously identified on the basis of CIDNP results [229, 230]. We begin with a discussion of the CIDNP investigations, since they preceded the ESR studies of all species but the prototype. 

As can be seen from Figure 17, the shapes of bands and are strongly influenced by the Jahn-Teller effect, i.e. by the distortion of the cyclopropane radical cation in its electronic ground state E and its first excited state E". For a discussion of this effect the reader is referred to work by Haselbach . 

Venkatesan, T. S., Mahapatra, S., Meyer, H. D., Kop-pel, H., 8c Cederbaum, L. S. (2007). Multimode Jahn-Teller and pseudo-Jahn-Teller interactions in the cyclopropane radical cation Complex vibronic spectra and nonradiative decay dynamics. The Journal of Physical Chemistry A, 111(10), 1746-1761. 

Figure 1. Potential energy diagram for cyclopropane in its ground state ( A/) and the two lowest states of its radical cation ( A, and 82). The vertical transition yields two bands (Jahn-Teller split) in the photoelectron spectrum.

Having discussed the electron-transfer reactions of cyclopropane derivatives in some detail, we only touch briefly on the related reactions of the larger ring systems. Cyclobutane, cyclohexane, and cyclooctane have degenerate HOMOs (Section 2.3.1) thus, their radical cations are Jahn-Teller active. It is reasonable to expect that suitable substitution will lift the degeneracy and favor one radical cation structure over the other. Qualitative predictions of the preferred structure are readily derived. 

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