Phenalenyl cations

PATr+ of about 0-2. Several methods for generating the phenalenyl cation have been developed.Because the center carbon is part of the conjugated system, the Huckel rule, which applies only to monocyclic conjugated systems, cannot be applied to just the peripheral conjugation. The nature of the phenalenyl system is considered further in Problem 12 at the end of this chapter. 

The orbital coefficients for the MO of energy a for the phenalenyl system described in Fig. 9.7 are as shown below. Predict the general appearance of the NMR spectra of the anion and cation derived from phenalene. 

The diagram below shows the distribution of the molecular orbitals for phenalenyl (Fig. 9.7). On the basis of these orbitals, predict the charge distributions for the cation. 

Allyl (27, 60, 119-125) and benzyl (26, 27, 60, 121, 125-133) radicals have been studied intensively. Other theoretical studies have concerned pentadienyl (60,124), triphenylmethyl-type radicals (27), odd polyenes and odd a,w-diphenylpolyenes (60), radicals of the benzyl and phenalenyl types (60), cyclohexadienyl and a-hydronaphthyl (134), radical ions of nonalternant hydrocarbons (11, 135), radical anions derived from nitroso- and nitrobenzene, benzonitrile, and four polycyanobenzenes (10), anilino and phenoxyl radicals (130), tetramethyl-p-phenylenediamine radical cation (56), tetracyanoquinodi-methane radical anion (62), perfluoro-2,l,3-benzoselenadiazole radical anion (136), 0-protonated neutral aromatic ketyl radicals (137), benzene cation (138), benzene anion (139-141), paracyclophane radical anion (141), sulfur-containing conjugated radicals (142), nitrogen-containing violenes (143), and p-semi-quinones (17, 144, 145). Some representative results are presented in Figure 12. 

A simple model which correlates the HOMO and LUMO of cycl-[3,3,3]azine with the degenerate nonbonding orbitals of [12]annulene accounts for the ESR spectra of the radical cations and anions of 2a and some derivatives. This model also predicts the almost identical rc-spin population observed for the 2a-cation and the isoelectronic phenalenyl... 

Examples of monocation dimer formation among aromatic hydrocarbons have been confined mostly to alternant hydrocarbons, and the dimer can be regarded as an association of two closed shell molecules which have lost an electron. Recently Paskovich and Reddoch (1972) made a new class of monocation dimers, in which an electron is missing from two associated open shell molecules. Oxidation of phenalene by oxygen led to the phenalenyl radical and, it is thought, to the phenalenyl cation, association of which gave the monocation dimer (93). 

Bowl-shaped carbocations (33) were obtained by alkylation of the parent corannulene. ° The cations were obtained as stable salts and characterized by X-ray analysis. Phenalenyl cations (e.g. (34)) were obtained as air-stable BPh4 salts. Observations made in a selective synthesis of l,2-di(organo)fullerenes led to a mechanism whereby a cationic fullerene intermediate is generated by Cu(ll) oxidation of a fullerene radical (or anion). ... 

The phenalenyl radical 4 represents the most fundamental and widely explored member in this family. Unlike typical stable neutral radicals such as TEMPO and a-nitronylnitroxide derivatives with a spin-localized nature, 4 is characterized by a planar, rigid structure with the spin spread over the whole molecular skeleton (Fig. 3). The resonance structures of 4 show that the spin density is predominantly at its oc positions, while the spin at the peripheral positions (jS positions) is much smaller, which can be explained by the spin polarization effect. In addition, 4 exhibits a high amphoteric redox ability with thermodynamically stable cation, neutral radical and anion species. All of these features of 4 lead to new insights in the field of physical chemistry. 

Nakasuji K, Yamaguchi M, Murata I, Yamaguchi K, Fueno T, Ohya-Nishiguchi H, Sugano T, Kinoshita M (1989) Synthesis and characterization of phenalenyl cations, radicals, and anions having donor and acceptor substituents three redox states of modified odd alternant systems. 

Small D, Zaitsev V, Jung Y, Rosokha SV, Head-Gordon M, Kochi JK (2004) Intermolecular Ti-Xo-Ti bonding between stacked aromatic dyads. Experimental and theoretical binding energies and near-IR optical transitions for phenalenyl radical/radical versus radical/cation dimerizations. J Am Chem Soc 126 13850-13858... 

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