Azulenic hydrocarbons

Azulene hydrocarbons yield intense blue spots at room temperature. Proazulenes appear as blue spots only after 10 min heating at 80° 0. The colours fade later and turn to green and yellow shades the intense blue can be regenerated by exposure to steam over a water bath. 

The generic term azulene was first applied to the blue oils obtained by distillation, oxidation, or acid-treatment of many essential oils. These blue colours are usually due to the presence of either guaiazulene or velivazulene. The parent hydrocarbon is synthesized by dehydrogenation of a cyclopentanocycloheptanol or the condensation of cyclopentadiene with glutacondialdehyde anil. 

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]... 

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, an isomer of naphthalene, lias a remarkably large dipole moment for a hydrocarbon (/i = 1.0 D). Explain, using resonance structures. 

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]... 

Of the fundamental nonalternant hydrocarbons, only two prototypes were known about fifteen years ago azulene (XI, Fig. 5), the molecular structure of which was determined by Pfau and Plattner and fulvene (XIX) synthesized by Thiec and Wiemann. Early in the 1960 s many other interesting prototypes have come to be synthesized. Doering succeeded in synthesizing heptafulvene (XX) fulvalene (XXI) and heptafulvalene (XXIII). Prinzbach and Rosswog reported the synthesis of sesquifulvalene (XXII). Preparation of a condensed bicyclic nonalternant hydrocarbon, heptalene (VII), was reported by Dauben and Bertelli . On the other hand, its 5-membered analogue, pentalene (I), has remained, up to the present, unvanquished to many attempts made by synthetic chemists. Very recently, de Mayo and his associates have succeeded in synthesizing its closest derivative, 1-methylpentalene. It is added in this connection that dimethyl derivatives of condensed tricyclic nonaltemant hydrocarbons composed of 5- and 7-membered rings (XIV and XV), known as Hafner s hydrocarbons, were synthesized by Hafner and Schneider already in 1958. 

On the other hand, in cata-condensed nonalternant hydrocarbons IV, VI, X and XI, peri-condensed nonalternant hydrocarbons XIV — XVIII, fulvenes XIX and XX, and fulvalenes XXI—XXIII, self-consistency was achieved only for the fully-symmetrical nuclear arrangement. All these molecule, except azulene pCl), also show in a greater or lesser degree a pronounced double-bond fixation. 

Sometimes the hydrocarbon is blue, probably owing to traces of an azulene. The contaminant is easily removed by dissolving the hydrocarbon in an equal volume of hexane or petroleum ether and shaking this solution with an equal volume of 85% syrupy phosphoric acid until the color has been removed. The hydrocarbon is then obtained on evaporation of the solvent it does not need redistillation. 

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... 

According to Kasha s rule, fluorescence from organic compounds usually originates from the lowest vibrational level of the lowest excited singlet state (Si). An exception to Kasha s rule is the hydrocarbon azulene (2) (Figure 4.5), which shows fluorescence from S2. 

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

This preference of photoreaction with a nucleophile at position 1 of azulene and naphthalene (4 and 2 in biphenyl, 9 in phenanthrene) is also evident upon considering the products from the reactions of derivatives of these hydrocarbons (Lok, 1972). In many other cases besides those represented in Figure 10 and equations (19) amd (20), the a-reactivity can be recognized as a major orientation rule. 

As mentioned for the relationship between the PE spectrum of a parent molecule and the electronic spectrum of its radical cation, any close correspondence between the electronic spectra of anions and cations or their hyperfine coupling patterns holds only for alternant hydrocarbons. The anions and cations of nonalternant hydrocarbons (e.g., azulene) have significantly different hyperfine patterns. Azulene radical anion has major hyperfine splitting constants (hfcs) on carbons 6, and 4,8 (flH = 0-91 mT, H-6 ah = 0-65 mT, H-4,8 ah = 0-38 mT, H-2) in contrast, the radical cation has major hfcs on carbons 1 and 3 (ah = 1.065 mT, H-1,3 Ah = 0.152 mT, H-2 ah = 0.415 mT, H-5,7 ah = 0.112 mT, H-6). °°... 

Azulene. The absorption spectrum of azulene, a nonbenzenoid aromatic hydrocarbon with odd-membered rings, can be considered as two distinct spectra, the visible absorption due to the 1Lb band (0-0 band near 700 nm) and the ultraviolet absorption of the 1L0 band.29 This latter band is very similar to the long wavelength bands of benzene and naphthalene CLb) and shows the same 130 cm-1 blue shift when adsorbed on silica gel from cyclohexane.7 As in the case of benzene and naphthalene, this blue shift is due to the fact that the red shift, relative to the vapor spectra, is smaller (305 cm"1) for the adsorbed molecule than in cyclohexane solution (435 cm"1). Thus it would appear that the red shifts of the 1La band are solely due to dispersive forces interacting with the aromatic molecule, in agreement with Weigang s prediction,29 and dipole-dipole interaction is negligible. 

Azo coupling of diazonium salts with aromatic (or pseudoaromatic) hydrocarbons is possible if the coupling agent is highly substituted. For example, azo compounds have been produced from pentamethylbenzene [12], benzpyrene [13], and azulene [1-4]. 

Direct irradiation of the (CH)10 hydrocarbon triquinacene (26) in pentane solution gave five different (CH)10 isomers along with some naphthaline and azulene. The two major products were pentacyclo[4.4.0.02 4.03 i0.05,9]dec-7-ene (27), arising from an intramolecular [2 + 2] cycloaddition, and hexacyclo[4.4.0.02,4.03,10.05,8.07 9]decane ( barettane , 28), which is formed via a di-n-methane rearrangement (see Section l.A.2.2.) followed by an intramolecular [2 + 2] cycloaddition,50... 

The observed spectra of some duroquinone-nickel complexes with olefins have been correlated by means of semiquantitative molecular-orbital theory by Schrauzer and Thy ret (48). In the case of n complexes of polynuclear hydrocarbons, such as naphthalene and anthracene, although their spectra are recorded, no conclusions have been drawn with regard to structure nor has any theoretical work been reported. Similar remarks apply to complexes of nonalternant hydrocarbons such as azulene. Although innumerable complexes of olefins with various transition metals are known and admirably reviewed (84), no theoretical discussion of even a qualitative nature has been provided of their electronic spectra. A recent qualitative account of the electronic spectra of a series of cyclopentadienone, quinone, and thiophene dioxide complexes has been given by Schrauzer and Kratel (85). 

Equally interesting is the situation in the second class of compounds studied (analogues of non-alternant hydrocarbons), which is best divided into two sub-groups analogues of the tropylium ion and analogues of azulene. The empirical correlation of experimental and theoretical excitation energies studied requires a further subdivision into compounds with one heteroatom (e.g. thiopyrylium ion) and two heteroatoms, either adjacent (e.g., 1,2-dithiolium ion) or non-adjacent (e.g., 1,3-dithiolium ion). Experimental and theoretical data are presented in Table VII. Table VIII summarizes data for the derivatives of dithiolia. Figure 15 shows the absorption curves of 1-benzo-... 

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