Cyclopropyl radical cation

It is not possible to describe the properties of the cyclopropyl radical cation correctly on the basis of the Walsh orbitals (see Section XI. C and, there, Reference 233). 

Krogh-Jespersen and Roth231 identified the 2B2 state as a transition state with one imaginary frequency and the 2A, state as the ground state of the cyclopropyl radical cation. At... 

FIGURE 23. First-order Jahn-Teller distortion of Dn symmetrical cyclopropyl radical cation. Geometries [UMP2/6-31G(d) calculations] and relative energy [CISD/6-31G(d)] from Reference 231... 

FIGURE 24. Pseudorotation cycle of the cyclopropyl radical cation. Relative energy [CISD/6-31 G(d)] of the2 A, ground state and the B2 transition state from Reference 231... 

Krogh-Jespersen and Roth231 also investigated Jahn-Teller distortions in mono-, di- and tetramethyl substituted cyclopropyl radical cations. In all cases, the ground state of the corresponding radical cation can be considered to be derived from a 2 4, -type state and (the) transition state(s) of pseudorotation from (a) 2B2-type state(s). Several minima and transition states were found along the pseudorotation path where the most stable form corresponds to an asymmetrical2A, -type state. 

Investigation of 1 upon removal of an electron has intrigued both theoreticians and experimentalists because the properties of the formed cyclopropyl radical cation provide a basis to test MO models of three-membered rings (the Walsh MO model cannot explain the properties of the cyclopropyl radical cation ). Ejection of an electron from the 3e MOs of 1 (MOs 11,12 in Figure 6) leads to the Jahn-Teller unstable electron configuration (see Section X), which can be stabilized by distortion to the C2v-symmet-rical states and 82 (first-order Jahn-Teller effect, see Figure 23). 

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