Azulene, aromaticity

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. 

Azulene is an aromatic compound and undergoes substitution reactions in the 1-position. At 270 C it is transformed into naphthalene. 

Among other aromatic compounds that have been tricyanovinylated are phenanthrene (23), o-alkylphenols (24), pyrrole (23), indoles (23,25), 2-meth5lfuran (26), azulenes (26,27), diazocyclopentadiene (28), and a variety of phenyUiydrazones (26). 

Polycyclic aromatic hydrocarbons, naphthylamines After application of the sample solution place the TLC plate in a darkened iodine vapor chamber (azulene a few minutes, PAH several hours). Then remove the excess iodine at 60 °C. [20]... 

Simple resonance theory predicts that pentalene (48), azulene (49), and heptalene (50) should be aromatic, although no nonionic canonical form can have a double bond at the ring junction. Molecular orbital calculations show that azulene should be stable but not the other two, and this is borne out by experiment. Heptalene has been prepared but reacts readily with oxygen, acids, and bromine, is easily hydrogenated, and polymerizes on standing. Analysis of its NMR spectrum shows that it is... 

In sharp contrast to 48 and 50, azulene, a blue solid, is quite stable and many of its derivatives are known. " Azulene readily undergoes aromatic substitution. Azulene may be regarded as a combination of 39 and 43 and, indeed, possesses a dipole... 

Aromatic hydrocarbons can be divided into two types alternant and nonalternant.In alternant hydrocarbons, the conjugated carbon atoms can be divided into two sets such that no two atoms of the same set are directly linked. For convenience, one set may be starred. Naphthalene is an alternant and azulene a nonaltemant hydrocarbon ... 

The reaction with disubstituted formamides and phosphorus oxychloride, called the Vilsmeier or the Vilsmeier-Haack reaction,is the most common method for the formylation of aromatic rings. However, it is applicable only to active substrates, such as amines and phenols. An intramolecular version is also known.Aromatic hydrocarbons and heterocycles can also be formylated, but only if they are much more active than benzene (e.g., azulenes, ferrocenes). Though A-phenyl-A-methyl-formamide is a common reagent, other arylalkyl amides and dialkyl amides are also used. Phosgene (COCI2) has been used in place of POCI3. The reaction has also been carried out with other amides to give ketones (actually an example of 11-14),... 

Polycyclic aromatic hydrocarbons, indole and quinoline derivatives, naphthylamines, azulenes Silica gel G Formation of oxidation products via the initially formed iodine complexes [15]... 

Katritzky and his colleagues have used equilibrium proto nation to estimate the aromaticity of furan and similar heterocycles using 2,5-di-tert-butylfuran as substrate in sulfuric acid. In agreement with the foregoing discussion, the furan does not behave as a Hammett (i.e., oxygen) base but as a carbon base similar to azulene. On Reagan s Hc scale, the furan gave n = 1.22, correspond-... 

The quasi-aromatic azulenes dissolve in 50-60% sulfuric acid, a property used in their isolation. The sulfuric acid solutions are yellow to orange rather than blue like the parent hydrocarbon, and they are... 

Clar, E. Aromatic Hydrocarbons. Part LVIII. The Structure of Azulene. 

Alkyl Shifts in Absorption Spectra of Azulene and other Aromatic Molecules. Proc. Phys. Soc. (London), Ser. A 65, 933 (1952). 

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

Theorem 24 Azulene and benzene are the fundamental units of even aromatic systems. 

Of the condensed nonbenzenoid aromatics, azulene (10) has gained greatest popularity [80]. Although it is an isomer of naphthalene, its electrochemical behavior... 

Halobenzenes < Benzene derivatives < Condensed aromatics Diphenylpolyenes < Azulene derivatives -Hb... 

With respect to the classes of aromatic compounds studied, it should be mentioned that bi- and tricyclic compounds (derivatives of naphthalene, azulene, biphenyl, phenanthrene, etc.), the reactions of which had incidentally been touched in the past, have received considerable attention in recent years. 

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