Abstract:The anion radicals of [18]annulene and of [6]annulene undergo Jahn−Teller distortions from the D
6
h
conformations of their respective neutral molecules. The conformation of lowest energy for the anion radical
of benzene has a C2
v
symmetry, and that for the anion radical of [18]annulene is D
2
h
. The very rapid pseudo-rotation of the benzene C2
v
system causes the six protons of the benzene anion radical to appear as if they
were equivalent in the EPR experiment. Fast pseudo-rotation rendering the uni… Show more
“…The remaining five carbons, on the other side of the nodal carbons, are twisted from planarity. Hence, the di -trans -C 12 H 12 anion radical undergoes pseudorotation around a “Mexican hat” in a manner that is analogous to that found in the benzene and [18]annulene systems …”
mentioning
confidence: 80%
“…As in the case of the [18]annulene anion radical,11b the pseudorotation is not fast on the EPR time scale, and the structure and spin densities oscillate as shown in Scheme . 5 …”
[reaction: see text] Low temperature (-100 degrees C) dehydrohalogenation of 1,2,5,6,9,10-hexabromocyclododecane (a common fire retardant) with potassium tert-butoxide in THF followed by one-electron reduction yields the anion radical of the di-trans form of [12]annulene. This system yields a well-resolved EPR signal that reveals that most of the spin density resides on one side (the planar side) of the anion radical. Five of the carbons in this [12]annulene system are twisted from the plane of the remaining seven carbons, and the rate of rearrangement between the degenerate conformations is on the EPR time scale (k = 10(6)-10(7) s(-1)). Warming of the solution results in the formation of a sigma-bond between the two internal carbons, loss of molecular hydrogen, and consequent generation of the anion radical of heptalene. Tractable quantities of neutral heptalene can be obtained via the reoxidation of this anion radical with iodine.
“…The remaining five carbons, on the other side of the nodal carbons, are twisted from planarity. Hence, the di -trans -C 12 H 12 anion radical undergoes pseudorotation around a “Mexican hat” in a manner that is analogous to that found in the benzene and [18]annulene systems …”
mentioning
confidence: 80%
“…As in the case of the [18]annulene anion radical,11b the pseudorotation is not fast on the EPR time scale, and the structure and spin densities oscillate as shown in Scheme . 5 …”
[reaction: see text] Low temperature (-100 degrees C) dehydrohalogenation of 1,2,5,6,9,10-hexabromocyclododecane (a common fire retardant) with potassium tert-butoxide in THF followed by one-electron reduction yields the anion radical of the di-trans form of [12]annulene. This system yields a well-resolved EPR signal that reveals that most of the spin density resides on one side (the planar side) of the anion radical. Five of the carbons in this [12]annulene system are twisted from the plane of the remaining seven carbons, and the rate of rearrangement between the degenerate conformations is on the EPR time scale (k = 10(6)-10(7) s(-1)). Warming of the solution results in the formation of a sigma-bond between the two internal carbons, loss of molecular hydrogen, and consequent generation of the anion radical of heptalene. Tractable quantities of neutral heptalene can be obtained via the reoxidation of this anion radical with iodine.
“…The radical anion of 6 was first observed by Sondheimer [87] and recently by Stevenson [88]. The main conclusion from these studies is that the structure is nonplanar, because of a Jahn-Teller distortion.…”
“…Conjugate polymers as a research of great contention give the probability to realize the Gentile particle model. − To be specific, we wish to show that cyclic hydrocarbon polyenes can be viewed as a realization of Gentile systems. Cyclic hydrocarbon polyenes, or simply N -annulenes, C N H N , denote the family of organic molecules that are monocyclic unsaturated hydrocarbons. − The electron paramagnetic resonance, , aromaticity, and fluorescence property are well investigated in the annulene systems. The Hückel model, a simple but effective molecular orbital model for describing planar conjugated molecules, − will be used to deal with N -annulenes.…”
Section: Introductionmentioning
confidence: 99%
“…Cyclic hydrocarbon polyenes, or simply N-annulenes, C N H N , denote the family of organic molecules that are monocyclic unsaturated hydrocarbons. 20−23 The electron paramagnetic resonance, 24,25 aromaticity, 26 and fluorescence property 27 are well investigated in the annulene systems. The Huckel model, a simple but effective molecular orbital model for describing planar conjugated molecules, 28−31 will be used to deal with N-annulenes.…”
The cyclic hydrocarbon polyenes with the general formula CNHN are called N-annulenes. In this paper, we discover that Gentile oscillators and N-annulenes in the Hückel approximation have the same energy spectra determined by the contact points of a regular polygon inscribed on a circle. This correspondence is derived from the symmetry of a C(n + 1) rotational group and dihedral group DihN. On the basis of their energy spectra, we further demonstrate that these two kinds of systems have the same partition functions and, thus, the same thermodynamics properties. N-annulenes can, therefore, be viewed as the natural realization of Gentile systems.
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