Pseudorotation path

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. 

Fig. 9. Orbital pattern of singly occupied molecular orbital and Jahn-Teller active mode. Both SOMOs are antisymmetric with respect to the cr plane. For corannulene (top) the tangential direction along the pseudorotational path at the minimum corresponds to the antisymmetric vibration, while, for coronene (bottom), the symmetric vibration corresponds to the tangential direction at the minimum.

The twist-boat-chair is chiral and hence there are actually two mirror-image or enantiomeric conformations. Correspondingly, there are two mirror-image pseudorotation paths to the twist-boat-chairs from the boat-chair, which is achiral. These paths are conveniently labelled by the mirror-image letters b and d. If we arbitrarily assign the letter h to the process shown in Fig. 3, and if we use the proton in the 1-equatorial position as a label, we can write down the effect of pseudorotation as shown in Table 6. 

The molecular structure and conformational dynamics of dioxadithiazocane (18) <80NJC179> were studied by x-ray and NMR analyses. Compound (18) was found to exist as two pseudo-enantiomorphic molecules. In the solid state, the molecule assumes two approximate boat-chair conformations with transannular sulfur-nitrogen distances of 2.94 A and 2.99 A. In CDCI3 and d(,-benzene solutions, the material exists as an enantiomeric equilibrium of two isoenergetic boat-chair forms involving a pseudorotational path <8UCS(P2)1554>. 

Fig. 2. Symmetry-unique portion of the pseudorotation path for H3, outer plates, around the Dih conical intersection point, center plates, as originally discussed by Longuet-Higgins [4]. Each point on the path is the constructed from (cos 0 Qy -h sinO Qx). Present drawing from Ref. [15]. The third internal coordinate, not shown, is the -preserving ring breathing mode, Qs...

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