Pentacene isomers

Figure 100. Pentacene isomers with labeled symmetry-non-equivalent benzene rings.

On the other hand, shock waves generate high pressures as well as high temperatures, and, consequently, some fector in addition to heat must be involved in the shock reactioa Drickamer [145], for example, has suggested a close relationship between photochemistry and liigh-pressure chemistry. He experimentally showed that high-pressure conditions promoted the formation of pentacene dimers with cross-linked structure, the formation of which usually occurred in the photochemical reaction. If the shock reaction is a type of some reactions in excited states such as a photochemical reaction, many valence isomers such as Dewar benzene and benzvalene would be generated from benzene by shock waves, and the interaction between these isomers would produce various com-poimds such as derivatives of fiilvene. Such valence isomers are imstable and would not have been detected in our study. 

IcosOnn). This is in good agreement with the experimental observation that the excitation energy of the L state (U) is 3.2 eV for anthracene but 4.0 eV for phenanthrene, while the energies of the next two singlet states (V and Y) are almost the same for both molecules. In Figure 2.18 similar results for the isomers of pentacene are compared with experimental data. 

Another indication that resonance might increase planarity is seen in Figure 3. Absorbance spectra for three similar PAHs are shown. The top spectrum is of tetrabenzo[a,cdj,Zra]perylene (compound 25), which results from the condensation of 7H-benz[cfe]anthracen-7-one with itself. The bottom spectrum is of dibenzo[j fc,wi)]dinaphtho-2,l,8,7-de/g 2, l, 8, 7 -opgr]pentacene (compound 33), which results from 6H-benzo[cfe]pyren-6-one condensation. The middle spectrum is of an isomer resulting from the condensation of 7H-benz[cfe]anthracen-7-one with 6H-benzo[de]pyren-6-one (compound 2). Although the three spectra are remarkably similar in band... 

The column packed with Sil-ODA shows very unique separation in RP-HPLC. Especially the uniqueness is emphasized when the solutes are PAHs. An extremely high separation factor, as compared with conventional ODS columns, is observed at temperatures below Tci e.g., the separation factor pentacene/chiysene IS 17.6 and 1.6 for Sil-ODA and conventional ODS columns respectively. To explain this unusual selectivity, we have proposed the multiple tt-tt interaction mechanism between PAHs and carbonyl groups of acrylate moieties in the ordered state.This interaction is quite possible according to our previous calculations and experiments 1) Fig. 3a shows the temperature dependencies of the separation factor a for geometrical isomers of stilbene. The poly(methyl acrylate) phase is less hydrophobic than Sil-ODA and ODS, as well as in a disordered state because of the absence of any long-chain alkyl groups, but the selectivity is distinctly higher than that in ODS. 2) A carbonyl-7T-benzene-TT interaction was simulated by the ab initio study. 

One of Clar s most notable early successes of the decade was pentacene 33. dar and John isolated 33 via dehydrogenation of a dihydropentacene isomer, several of which had been laboriously produced since 1911 when Phillipi first claimed one as 33 [28]. The combination of two groups efforts provided a far simpler route to pentacene two decades later. The highly efficient route began with condensation of o-phthalaldehyde and cydohexane-l,4-dione to afford quinone 34 (Scheme 1.10) [29]. Reduction with A1 powder afforded 33 in two steps [30]. Clar and coworkers also synthesized several pentacene derivatives in the 1940s 1.2-benzopentacene from pseduocumene and three additional dibenzopentacene derivatives from naphthalene and/or phenanthrene starting materials [la]. The syntheses focused on condensation cydization reactions of keto-adds to form the penultimate quinones and ultimate polycydes. 

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