Anthracene higher acenes

Generally, benzene and naphthalene derivatives show only little reactivity as dienes in Diels-Alder synthesis, contrary to anthracene and the higher acene derivatives which are frequently used as dienes. Exceptions are the reactions of benzene and naphthalene derivatives with highly reactive dienophiles such as dicyanoacetylene (DCA), which... 

Naphthalene, Anthracene, and Linear Polyacenes Linear polyacenes possess two low-lying excited states, which in the Platt notation used in spectroscopy, are labeled as La and Lb the former is Biu and the latter is 1 B2u (7,19). The Biu state is a monoionic state, while B2U is a covalent excited state, which as in benzene, is dipole forbidden, but can be accessed by two photon spectroscopy. In naphthalene and anthracene, is the second excited state, but in higher acenes, becomes the first excited state (16,19). We will now show how to construct and conceptualize this excited state. Already at the outset, we encounter here a problem of choice, namely, that the set of covalent Rumer VB structures involves many structures (e.g., 42 in naphthalene), and one has to restrict the VB structure set in order to understand the constitution of these... 

Oxidation of anthracene or higher acenes also occurs in the absence of a dye, since the same substrates act as sensitizers in singlet oxygenation [9c,42a]. These compounds react mainly at the mexo-positions of the aromatic nucleus [49a], but electron-donating groups have a strong directing effect when placed at the 1- and 4-positions (Sch. 33) [49b]. 

The charge densities for the anions can be displayed in HYPERCHEM as illustrated in Figure 7.5, where the charges on C and H are shown for the naphthalene anion. The Values of the linear acenes vary from —0.06 to 0.26q for benzene to —0.05 to 0.15q for naphthalene, to 0.04 to 0.18q for anthracene and tetracene. For pentacene the range is lowered to 0.03 to 0.14q. Thus, the solution energy differences should be smaller for the higher acenes and fullerenes. In predicting the reduction potential value for heptacene, this variation should be included. The reduction potential based on a value of 0.6 V versus Hg pool for hexacene is predicted to be —0.5 V versus the Hg pool. The value, if we assume a constant... 

Twisted naphthalenes, anthracenes, and higher acenes have been reviewed recently [8]. Only a brief summary of representative examples is given in this section. 

While it is in the triplet state a molecule may undergo typical diradical reactions. This provides a plausible mechanism for radical-like reactions of substances that are largely diamagnetic. They are partly converted to the triplet state by light, or in the case of low lying triplet states, by heat. Probable examples of this mechanism are the photooxidation of rubrene and the photooxidation and dimerization of anthracene and higher members of the acene series.76... 

In contrast to anthracene or higher members of the acene series [45], naphtalene does not react with singlet oxygen [19a]. The reaction occurs readily when electron-donating substituents are introduced on the 1,4... 

The calculated MINDO/3 LUMOs for these molecules are lower than the experimental Ea by 0.70 eV and for AMI are higher than the experimental Ea by about 0.1 eV. These are shown in Figure 7.2. The systematic uncertainties remain constant. Figure 7.3 provides the optimum values of the VEa for the linear acenes. The VEa are between the A Ea and MINDO/3 LUMO values. The calculated VEa for hexa-cene to novacene support the AEa values of 1.65 eV to 2.0 eV. The systematic difference is the rearrangement energy. It is approximately 0.2 eV for anthracene and above. 

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