Permutation symmetry control: higher-order permutations in the valence bond method

Abstract

The application of the Valence Bond method to the theoretical description of concerted reactions furnishes an example of the importance of higher-order permutations.

Using Valence Bond Theory to Understand Electronic Excited States: Application to the Hidden Excited State (2Ag) of C2nH2n+2(n= 2−14) Polyenes

“…An interesting feature in Table is the relative sign of mixing of R 1 and R K , which is precisely as in the corresponding antiaromatic/aromatic cyclic species, ,− and may be understood based on the sign alternation of the overlap (and hence also of the reduced matrix element) between R 1 and R K which is given by (−1/2) n -1 in eq 12.…”

A Different Story of π-DelocalizationThe Distortivity of π-Electrons and Its Chemical Manifestations

“…The bonding combination of the Kekulé structures is a delocalized electronic state and can be described by the resonating linear combination of the two structures, eq 1 Here, the sign of the ground-state combination depends on the parity ( p ) of the systems and is determined by the sign of matrix elements between the Kekulé structures. ,, As a rule, whenever the ground state behaves as the totally symmetric representation of the respective point group, the parity is even and the combination is positive, while when the ground state is not totally symmetric, the parity is odd and the wave function is the negative combination. For example, for H 6 , Li 6 , π-benzene, etc., with totally symmetric ground states, the positive combination is the ground state and the same applies to all A n species which fall into the aromatic category ( n = 4 N + 2).…”

On the size of the singlet-triplet energy gap in trimethylenemethanes

“…98, 2358(1976). (11) If the benzene matrices contained high local concentrations of dimethyl fumarate, one might imagine that entrapment of the singlet 1-S could occur in the cascade from photoexcited diazene 2, before spin equilibration. However, continuous irradiation of diazene 2 in a benzene matrix at 98 K leads to a rapid buildup of the triplet ESR signal followed by a slow decay due to a secondary photoreaction of the triplet.…”