Spontaneous Symmetry Breaking in Matter Induced by Degeneracies and Pseudodegeneracies

Pseudo Jahn-Teller Effect in Puckering and Planarization of Heterocyclic Compounds

“…From general space-symmetry considerations, one would expect that in an isotropic environment any molecular system should have the highest possible symmetry, but in fact we see that in many cases the symmetry of the system is International Journal of Organic Chemistry much lower (see [1]). In this respect, cyclic molecules (including the heterocyclic ones) should be at least planar, and any deviation from the planar structure (puckering) can be described through the instability of the reference planar high-symmetry nuclear configuration.…”

“…In [24] 3,8-diiodo-dibenzo [1,2]dithiine was investigated both theoretically and experimentally as a potential molecular system which can act as a memory sto-International Journal of Organic Chemistry rage bank. It was shown that the neutral molecule is slightly twisted around the central axis whereas two-electron reduction of this compound causes S-S bond cleavage and significant structural rearrangement [24].…”

“…A general approach to handle instabilities and structural changes in molecular systems in non-degenerate states is the pseudo Jahn-Teller effect (PJTE). It was proved that the PJTE is the only source of instability of high-symmetry configurations of molecules or solid in non-degenerate states (See, e.g., the monographs [2] [3], and the reviews [1] [4] [5] and references therein). The phenomenon of puckering as due to the PJTE was first formulated in [3], and then employed to explain the origin of the out-of-plane distortions of a variety of cyclic and heterocyclic systems [6]- [11].…”

“…In Section 3, the possibility of flattening the 1,4-dithiine containing compounds by suppressing the PJTE via oxidation is discussed. The enhancement of the PJTE induced distortion by reduction is analyzed in Section 4 using the dibenzo [1,2]dithiine molecule as an example. In the last Section 5, the change of the PJTE by chemical substitution, accompanied by a change in the structure of heterocyclic compounds, is discussed using, as examples, 1,4-ditinine and its S-oxygenated derivatives.…”

“…leads to enhancement of the PJTE and as a result, to a much stronger distortion of the dianion compared with the neutral molecule. In the present paper we present the results of the electronic structure and PJTE investigation of dibenzo[1,2]dithiine molecule, C 12 H 8 S 2 . For this purpose the electronic structure calculations and vibrational frequency analysis for C 12 H 8 S 2 and (C 12 H 8 S 2 ) 2− molecules were carried out in their reference planar nuclear configuration of C 2v symmetry.…”