Electron naphthalene

Molecular orbital calculations snggest that the jr electrons in naphthalene are delocalized over the two rings and this results in substantial stabilization. These molecules are planar, and all p orbitals are suitably aligned for overlap to form n bonding molecular orbitals. Although we can draw Kekule structures for these compounds, it is strictly incorrect to use the circle in hexagon notation since the circle represents six jr electrons. Naphthalene has 10 carbons, and therefore 10 jr electrons, and anthracene has 14 jr electrons. The circle notation suggests 12 or... 

Thus, 87 gives a satisfactory picture for a ten w-electron naphthalene-like system, but the localization of charges is unsatisfactory because abundant chemical evidence shows that carbon atoms numbered 2 and 5 are more positive than carbon atoms 3 and 4, and according to 87, mesomeric displacement of the negative charge on atom 3a would lead to the opposite conclusion. 

Thus the benzo-1,2-dithiolium ion (20c), which is of interest for comparative studies with the iso-ir-electronic naphthalene, the benzotropylium ion,26a the 1-thianaphthalinium ion,28-30 and the 2-thianaphthalinium ion,27 can be obtained in good yield via the cyclic mercapt l (21) (R1/R2=C4H4 R3=H).26... 

Both pyracyclene (133) (which because of strain is stable only in solution) and dipleiadiene (134) are paratropic, as shown by NMR spectra. These molecules might have been expected to behave like naphthalenes with outer bridges, but the outer n frameworks (12 and 16 electrons, respectively) constitute antiaromatic systems with an extra central double bond. With respect to 133, the 4n + 2 rule predicts pyracylene to be aromatic if it is regarded as a 10-7i-electron naphthalene unit connected to two 2-7t-electron etheno systems, but antiaromatic if it is viewed as a 12-7t-electron cyclododecahexaene periphery perturbed by an internal cross-linked etheno unit. Recent studies have concluded on energetic grounds that 133 is a borderline case, in terms of aromaticity-antiaromaticity charac-... 

The. more tightly held an electron is. the more difficult it is to remove, hence the higher the electrode potential necessary to remove it. Make the reasonable hypothesis that the electron removed in a one-electron oxidation comes from the highest occupied orbital. HOMO. Using SHMO. determine the HOMO for ben7 ene, biphenyl, and naphthalene. 

The purpose of this eornpuLer project is Lo examine several polynuclear aromatic hydrocarbons and to relate their electron density patterns to their carcinogenic activity. If nucleophilic binding to DN.A is a significant step in blocking the normal transcription process of DN.A, electron density in the hydrocarbon should be positively correlated to its carcinogenic potency. To begin with, we shall rely on clinical evidence that benzene, naphthalene, and phenanthrene... 

Indole is classified as a 7c-excessive aromatic compound. It is isoelectronic with naphthalene, with the heterocyclic nitrogen atom donating twm of the ten 7t-electrons. 

Indole is a heterocycHc analogue of naphthalene. The basic reactivity patterns of indole can be understood as resulting from the fusion of an electron-rich pyrrole ring with a ben2ene ring. 

Sodium naphthalene [25398-08-7J and other aromatic radical anions react with monomers such as styrene by reversible electron transfer to form the corresponding monomer radical anions. Although the equihbtium (eq. 10)... 

PEN film for audio- and videotape and various electronic appHcations and blow molded PEN containers for hot-fill appHcations are already being marketed in Japan. NDA is unlikely to ever become as inexpensive as terephthaUc acid but novel NDA-based polyesters will become available if a market need exists. One example could be the experimental polyester PBN (Celanese Corp.) this is the NDA analogue of PBT, poly(l,4-butylene naphthalene-2,6-dicarboxylate) [28779-82-0]. It has a high rate of crystallization, faster even than that of PBT, and its combination of physical properties is weU-suited for injection molding. 

Benzene rings can also be fused in angular fashion, as in phenanthrene, chrysene, and picene. These compounds, while reactive toward additions in the center ring, retain most of the resonance energy per electron (REPE) stabilization of benzene and naphthalene. ... 

The antiaromatic twelve r-electron benzodithiadiazine 12.12 (R = H), an inorganic naphthalene analogue, is obtained as a volatile deep-blue solid by the reaction of PhNSNSiMcs with SCI2, followed by an intramolecular ring closure with elimination of HCl (Scheme 12.2). ... 

One way to anticipate the favored product is to consider the shape of naphthalene s best electron-donor orbital, the highest-occupied molecular orbital (HOMO). Display the HOMO in naphthalene and identify the sites most suitable for electrophilic attack. Which substitution product is predicted by an orbital-control mechanism Ts this the experimental result ... 

The orbital model would be exact were the electron repulsion terms negligible or equal to a constant. Even if they were negligible, we would have to solve an electronic Schrodinger equation appropriate to CioHs " " in order to make progress with the solution of the electronic Schrodinger equation for naphthalene. Every molecular problem would be different. 

The pyridopyrimidines possess the same 7r-electron structure as naphthalene. The electronic transitions between the 77-orbitals would therefore be expected to give rise to similar ultraviolet spectra. As in the case of the quinazolines and the pteridines, this has proved to be so. 

The reactivities of 4- and 2-halo-l-nitronaphthalenes can usefully be compared with the behavior of azine analogs to aid in delineating any specific effects of the naphthalene 7r-electron system on nucleophilic substitution. With hydroxide ion (75°) as nucleophile (Table XII, lines 1 and 8), the 4-chloro compound reacts four times as fast as the 2-isomer, which has the higher and, with ethoxide ion (65°) (Table XII, lines 2 and 11), it reacts about 10 times as fast. With piperidine (Table XII, lines 5 and 17) the reactivity relation at 80° is reversed, the 2-bromo derivative reacts about 10 times as rapidly as the 4-isomer, presumably due to hydrogen bonding or to electrostatic attraction in the transition state, as postulated for benzene derivatives. 4-Chloro-l-nitronaphthalene reacts 6 times as fast with methanolic methoxide (60°) as does 4-chloroquinoline due to a considerably higher entropy of activation and in spite of a higher Ea (by 2 kcal). ... 

It is notable that pyridine is activated relative to benzene and quinoline is activated relative to naphthalene, but that the reactivities of anthracene, acridine, and phenazine decrease in that order. A small activation of pyridine and quinoline is reasonable on the basis of quantum-mechanical predictions of atom localization encrgies, " whereas the unexpected decrease in reactivity from anthracene to phenazine can be best interpreted on the basis of a model for the transition state of methylation suggested by Szwarc and Binks." The coulombic repulsion between the ir-electrons of the aromatic nucleus and the p-electron of the radical should be smaller if the radical approaches the aromatic system along the nodal plane rather than perpendicular to it. This approach to a nitrogen center would be very unfavorable, however, since the lone pair of electrons of the nitrogen lies in the nodal plane and since the methyl radical is... 

The aromaticity of naphthalene is explained by the orbital picture in Figure 15.12. Naphthalene has a cyclic, conjugated it electron system, with p orbital overlap both around the ten-carbon periphery of the molecule and across the central bond. Since ten 77 electrons is a Hiickel number, there is tt electron delocalization and consequent aromaticity in naphthalene. 

Figure 15.12 An orbital picture and electrostatic potential map of naphthalene, showing that the ten tt electrons are fully delocalized throughout both rings.

Just as there are heterocyclic analogs of benzene, there are also many heterocyclic analogs of naphthalene. Among the most common are quinoline, iso-quinoline, indole, and purine. Quinoline, isoquinoline, and purine all contain pyridine-like nitrogens that are part of a double bond and contribute one electron to the aromatic it system. Indole and purine both contain pyrrole-like nitrogens that contribute two - r electrons. 

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