Naphthalene, aromaticity resonance

The difference, -255kJ/mol, is naphthalene s resonance energy. Naphthalene is less aromatic than benzene because a per-ring resonance energy of j(-255) = -127.5 kJ/mol is smaller in absolute value than that of benzene (-150 kJ/mol). 

Polycyclic aromatic compounds also undergo electrophilic aromatic substitution reactions. Because the aromatic resonance energy that is lost in forming the arenium ion is lower, these compounds tend to be more reactive than benzene. For example, the brotni-nation of naphthalene, like that of other reactive aromatic compounds, does not require a Lewis acid catalyst ... 

Just as for naphthalene, the regiochemistry of attack is readily interpreted by looking at possible intermediates those for attack at C-5/8 allow delocalisation of charge without disruption of the pyridinium ring aromatic resonance, while those for attack at C-6/7 would necessitate disrupting that resonance in order to allow delocalisation of charge. 

In general the most stable resonance structure for a polycyclic aromatic hydro carbon is the one with the greatest number of rings that correspond to Kekule formula tions of benzene Naphthalene provides a fairly typical example... 

The accepted configuration of naphthalene, ie, two fused benzene rings sharing two common carbon atoms in the ortho position, was estabUshed in 1869 and was based on its oxidation product, phthaUc acid (1). Based on its fused-ring configuration, naphthalene is the first member in a class of aromatic compounds with condensed nuclei. Naphthalene is a resonance hybrid ... 

The addition product, C QHgNa, called naphthalenesodium or sodium naphthalene complex, may be regarded as a resonance hybrid. The ether is more than just a solvent that promotes the reaction. StabiUty of the complex depends on the presence of the ether, and sodium can be Hberated by evaporating the ether or by dilution using an indifferent solvent, such as ethyl ether. A number of ether-type solvents are effective in complex preparation, such as methyl ethyl ether, ethylene glycol dimethyl ether, dioxane, and THF. Trimethyl amine also promotes complex formation. This reaction proceeds with all alkah metals. Other aromatic compounds, eg, diphenyl, anthracene, and phenanthrene, also form sodium complexes (16,20). 

The polycyclic aromatic hydrocarbons such as naphthalene, anthracene, and phenan-threne undergo electrophilic aromatic substitution and are generally more reactive than benzene. One reason is that the activation energy for formation of the c-complex is lower than for benzene because more of the initial resonance stabilization is retained in intermediates that have a fused benzene ring. 

All polycyclic aromatic hydrocarbons can be represented by a number of different resonance forms. Naphthalene, for instance, has three. 

Azulene, a beautiful blue hydrocarbon, is an isomer of naphthalene. Is azulene aromatic Draw a second resonance form of azulene in addition to that shown. 

A general theory of the aromatic hydrocarbon radical cation and anion annihilation reactions has been forwarded by G. J. Hoytink 210> which in particular deals with a resonance or a non-resonance electron transfer mechanism leading to excited singlet or triplet states. The radical ion chemiluminescence reactions of naphthalene, anthracene, and tetracene are used as examples. 

Naphthalene-2,3-dicarboxaldehyde Nicotinamide adenine dinucleotide N-Acetylneuraminic acid 4-Fluoro-7-nitrobenzoxadiazole Naphthalene-2,3-dicarboxaldehyde Nondestructive readout Near infrared Near infrared fluorescence Nuclear magnetic resonance 2-Nitrophenyl oxalate 1,1 -Oxalyldiimidazole Polycyclic aromatic hydrocarbon Principal component analysis Photosensitized chemiluminescence Pentachlorophenyl oxalate Polymerase chain reaction... 

A reaction analogous to the formation of metal ketyls is the formation of negative ion-radicals not only from aromatic nitro compounds but also from aromatic hydrocarbons like naphthalene. These substances are highly colored and exhibit paramagnetic resonance absorption.128... 

Theorem 23 Azulene should be semi-aromatic, having resonance energies intermediate between corresponding decapentaene and naphthalene derivatives. 

This may be rationalized by considering the stability of intermediate addition cations. When the electrophile attacks at C-5 or C-8, the intermediate cation is stabilized by resonance, each having two favourable forms that do not perturb the aromaticity of the pyridinium system. In contrast, for attack at C-6 or C-7 there is only one such resonance form. We used similar reasoning to explain why naphthalene... 

One can predict that singlet 1-naphthylnitrene will cyclize more readily than phenylnitrene because the resonance energy per aromatic ring is lower in naphthalene than benzene, but by the same token, 1-naphthylnitrene should cyclize more slowly than vinylnitrene. 

Similarly, the fusion of an aromatic ring to the oxepin-benzene oxide system was found to drive the equilibrium toward extremes in either direction. The calculated resonance energies for oxepins (26), (27) and (28) were 4.81, 78.46 and 81.72 kJ mol-1 respectively (70T4269). These calculated values concur with experimental observations since oxepins (27) and (28) have been synthesized and are relatively stable compounds. The formation of 2-benzoxepin (26) from naphthalene 1,2-oxide would involve a considerable loss in resonance energy to the system and has not been detected spectroscopically (67AG(E)385). 

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