Naphthalene systems

Naphthalene is not easily adaptable to provide different substitution patterns but the most structurally suitable system for providing nematic phases has 2,6-disubstituents, which can fortunately be derived from the available 6-bromonaphth-2-ol (1). Here selectivity of coupling can be achieved with the triflate derivatives (2 and 3 which couple preferentially at the triflate and iodo site respectively) [16, 26] the iodo compounds can be obtained from bromo compounds by an efficient procedure [80, 81]. 

6-Alkylnaphthalene-2-carboxylates [82] have been prepared in a similar way to benzoate esters and they give compounds with values 60-80°C higher comparable increases (= 80-90 °C) are obtained by replacing a benzene by naphthalene in cyano-biphenyls [83-85]. A naphthalene ring also has several possible states of reduction ranging from the dihydro compound to the 

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Fig. 6. Dyes for WORM media phthalocyanine derivatives. The basic stmcture (12) of naphthalocyanine derivatives. Y = Si, Ge, Sn, Al, Ga, In, or a transition metal = ORj, OSiR R R, polymer. and represent substituents on the tings of the naphthalene system.

Phenanthrene and anthracene both react preferentially in the center ring. This behavior is expected from simple resonance considerations. The c-complexes that result from substitution in the center ring have two intact benzene rings. The total resonance stabilization of these intermediates is larger than that of the naphthalene system that results if substitution occurs at one of the terminal rings. ... 

Both of these approaches have been attempted, and both are substantially equivalent for heterocyclic (e.g. quinoline and isoquinoline) and homocyclic (naphthalene) systems. Consequently, in the subsequent discussion it is fruitful to include the available work on naphthalene derivatives. In the case of the fused six-membered rings, Eq. (3) is not applied because it does not permit treatment of the 5- and 8-positions, and the available series as a whole are too short to make this treatment useful. 

Extensions to other reactions and to other aza-naphthalene systems is obvious. The chemical equivalence between formally identical positions in all possible situations must be established experimentally. In this connection, caution should be used because for some of the above positions steric hindrance may become an important factor in determining the overall reactivity. 

Some additional derivatives containing extended 7t-systems in place of the benzene nucleus are naphthalene, anthracene (2,3-Ac) and phenanthrene (9,10-Phc). They also belong to the phthalocyanine family. For the naphthalene system two types of macrocyclcs, the 1,2-naph-thalocyanine (1,2-Nc) and the 2,3-naphthalocyanine (2,3-Nc), are known. 

In the reaction of the strongly electrophilic 4-nitrobenzenediazonium ion with 2-naphthol-6,8-disulfonic acid, which yields a sterically hindered o-complex, Roller and Zollinger (1970) actually observed the rapid formation of a 7T-complex spec-trophotometrically at low pH. The concentration of the 7T-complex decreases slowly and at the same rate as that of the formation of the azo product. H NMR data indicate that the 7t-complex is not localized. All 7T-electrons of the benzene and the naphthalene system are involved in the complex formation to a similar degree, in... 

These studies have recently been extended to the naphthalene system.(142) In alkaline media 2-methoxy-5-nitro-, l-methoxy-6-nitro-, and 2-methoxy-7-nitro-naphthalenes all undergo photosubstitutions to produce naphthols ... 

The phenanthrene system appears to be no more easily cleaved than the naphthalene system however, ethyl anthracene is clearly destabilized significantly more than the other compounds in the table. The large decrease in bond-dissociation energy for the anthracene system is reflected in the increase by three to four orders of magnitude in the rate of scission at conversion temperatures, as shown in the table. 

Other nucleophile-electrophile pairs for which the pm-disubstituted naphthalene system has been used to monitor potential bonding interactions are illustrated in [35] and [36], The methoxynitrile [35], for example, shows the same sort of evidence for a bonding interaction, marked by a 7° distortion from linearity at the nitrile carbon, in plane, and exactly away from the methoxyl oxygen (Procter et al., 1981) so also does the bipyridyl dinitrile [37] (Baxter et al., 1991). In the unique case of the 8-diazonium quinoline-N-oxide [36] the proximity of a formally negatively charged oxygen induces a distortion from linearity of 10.4° in the diazonium group (Wallis and Dunitz, 1984). 

Oxadiazole (1 R = R = H) is calculated to be 8.9 kcal moU less stable than its open chain tautomer (2) (85AG(E)713>. On the other hand, 1,2,3-benzoxadiazole is about 1 kcal mol more stable than 2-diazocyclohexadienone (91JST(247)135>. The position of the equilibrium is markedly affected by substituents. The benzoxadiazole (4) is more stable than its tautomer (5) by about 1.5 kcal mol but tetrafluorobenzoxadiazole is substantially less stable than the corresponding diazocarbonyl isomer. The open-chain forms are also favoured by polar solvents and by hydrogen bonding. In the naphthalene series, the stabilization of the fused oxadiazole (6) relative to its open chain tautomer can be ascribed to partial bond fixation in the naphthalene system, which disfavours... 

Ph) has been reported to proceed smoothly to give, as expected, the corresponding 3-Cp-nitrophenyl) and 3-(p-bromophenyl) derivatives. Gibson found that the betaine (132, R = Me) dissolved in sulfuric acid to give a blue solution, a result which is consistent with sulfonation in the naphthalene ring system, and also reported that the same compound reacted smoothly with bromine in acetic acid to give a tetrabromo derivative in which all the bromine atoms were located in the naphthalene system. The structure of this compound was not, however, established. ... 

Halogenation of perimidines, perimidinones, and dihydroperimidines occurs at an ortho- or /) 7ra-position in the naphthalene system, that is, the 4-, 6-, 7-, 9-positions in the perimidine system, where the donor effects from the nitrogens operate <1981RCR816, 1995AQ151>. 

TMS derivatives, respectively, without the formation of peri-substituted products, as observed in the corresponding naphthalene systems. 6- and... 

The transition from CT excited state to triplet state has been shown for the TMPD-a-methyl naphthalene system. The triplet level of naphthalene is considerably lower than the CT level of this pair (20). 

An electrochemical method can also be used for the reduction of both rings of the naphthalene system 399) ... 

Srinivasan, C., Perumal, S., Arumugam, N., and Murugan, R., Linear free-energy relationship in naphthalene system-substituent effects on carbon-13 chemical shifts of substituted naphthylmethyl sulfides, Ind. J. Chem., 25A, 227, 1986. 

In the closed conformation the carbonyl group is orientated towards the naphthalene system, and consequently its Si-face is blocked such that only the Re-face is available to react with an incoming alcohol nucleophile. The relative orientation of the nucleophile was also suggested to be ordered by 7t-7r-staclcing interactions because sec-alcohol nucleophiles incorporating an electron-rich aryl amide gave the highest selectivities. 

Three types of cycloaddition products are generally obtained (Sch. 1). While [2+2] (ortho) and [2+3] (meta) cycloaddition are frequently described, the [2+4] (para or photo-Diels-Alder reaction) pathway is rarely observed in benzene ring systems. With naphthalene systems however, the para cycloaddition occurs more frequently [6,8]. The photo-Diels-Alder reaction and other photocyclization reactions are also observed with anthracene derivatives and higher condensed aromatic compounds. However, these reaction are not treated in this chapter since they are caused by the particular photophysical and photochemical properties of these compounds [6,9]. 

Synthesis of tricyclic compounds containing a 4- to 7-membered heterocycle peri-annelated to a naphthalene system 90AHC(51)1. 

A special application of the haptotropic rearrangement is the reaction of diastereopure complex 59a (Section 8.3.4, Scheme 23). Upon warming to 90 °C in di-n-butyl ether, haptotropic migration of the chromium tripod occurs intramolecularly along the same face of the naphthalene system to produce pure diastereomer 59c (Scheme 25) [57d]. 

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