Naphthalenium

Draw Lewis structures (or a series of Lewis structures) for the intermediate ions formed by addition of N02 to naphthalene at the 1 and 2 positions (nitro-naphthalenium ions ). On this basis, are you able to anticipate which intermediate is likely to be the more stable Examine the energies of 1-nitronaphthalenium and 2-nitronaphthalenium ions to see which ion is actually more stable. Which substitution product should be favored Is this the same product anticipated by inspection of naphthalene s HOMO Is it the observed product ... 

It was also possible to prepare stable ethylene-(4-X)-naphthalenium ions 115 (X= Me, Ph, OMe) and 9,9-ethylene-(10-X)-anthracenium ions 116 (X = H, Br) under long-lived stable ion conditions114. 

The only conjugate acid of a substituted benzene for which pAR can reasonably be estimated is the protonated toluene. A value of AG ( (aq) for the corresponding hydrate is readily estimated from the likely effect of methyl substitution on the stability of 1,4-benzene hydrate,47 and this can be used to estimate pAn2o as described above, while pAR is obtained from pAR = pAh2o + pAa. The resulting pK values are compared below with those for the corresponding methyl-substituted naphthalenium 19 and anthracenium 20 ions, for which reactions of the hydrates (or their methyl ethers) have been... 

Cycloalkadienyl cations, particularly cyclohexadienyl cations (benzenium ions), the intermediate of electrophilic aromatic substitution, frequently show remarkable stability. Protonated arenes can be readily obtained from aromatic hydrocarbons244 251 in superacids and studied by 1H and 13C NMR spectroscopy.252,253 Olah et al.252 have even prepared and studied the parent benzenium ion (C6H7+) 88. Representative 1H NMR spectra of benzenium253 and naphthalenium ions25488 and 89 are shown in Figures 3.11 and 3.12, respectively. 

The naphthalene complex of [Os] (3) reacts with triflic acid to form a /3-lH-naphthalenium species, which has been characterized at —40 °C [16]. Unfortunately, most nucleophiles react as bases with this species and return the naphthalene complex. However, MMTP and the mild hydride donor triethylsilane (Table 4, entries 1 and 2) both add to C4 of the complex and yield 1,4-dihydronaphthalenes in moderate overall yield following decomplexation [17]. 

Methyl vinyl ketone (entry 3) and the tert-butyl cation (entry 4) are also reactive toward complex 3. The naphthalenium complexes resulting from the addition of these electrophiles will add the conjugate base of dimethyl malonate (generated in situ from a combination of dimethyl malonate (DMM) and diisopropylethylamine (DIEA)) to complete the tandem additions. Oxidation of the resulting complexes yields cis-l,4-dihydronaphthalenes. The entire sequence of complexation, tandem addition, and demetalation employed for all entries in Table 4 can be performed using bench-top conditions (i.e., a non-inert atmosphere). 

As mentioned in the introduction, one of the major advantages of using transition metals for dearomatization is that they allow the isolation of reaction intermediates and, consequently, broaden the range of accessible manipulations. For example, when the naphthalene complex of [Os] (3) is treated with dimethoxymethane in the presence of HOTf, the resulting 3-lH-naphthalenium species 23 can be isolated in 88 % yield and stored for days at room temperature (Table 5). The electrophile adds anti to the face involved in metal coordination and pushes the proton at Cl toward the metal, which prevents spontaneous rear-omatization. As shown in Table 5, 23 reacts with MMTP, the conjugate base of dimethyl malonate, 2-trimethylsiloxypropene, tetrabutylammonium cyanoborohydride (TBAC), dime-... 

The naphthalenium (106) and anthracenium (107) analogs of 106 have also been prepared, and the neutral species 108 was isolated from solvolysis of a p-ethylphenolate derivative . 

SbF5-FS03H—SO2CIF-SO2F2 solution at the naphthalenium ion (31) at -90 °C... 

Extensive studies of naphthalenium cations were later reported by Lammertsma and Cerfontain.1314 Figure 2 summarizes the H NMR data and A<513C values for a series of isomeric monomethyl-, dimethyl-, trimethyl-, and tetramethylnaphthalenium, as well as for hexahydropyrenium mono- and dications. Methyl groups exert strong directive and charge-stabilizing effects. The hexahydropyrenium dication shows dramatic charge localization in the ortho positions. Ipso protonation is observed with 1,4,5-trimethyl and 1,2,3,4-tetramethyl derivatives. 

Fig. 2. Compilation of H NMR and A5I3C values for alkylated naphthalenium ions.

In contrast to the reactivity pattern seen for heteroatom-substituted arene complexes, tandem addition reactions with benzene and naphthalene generally provide 1,4-addition products. This outcome is thought to be the result of C4 of the corresponding naphthalenium (resonance contributors 100-102) or benzenium (resonance contributors 95-97) having a greater partial positive charge because of its overlap/delocalization with the adjacent 71 system (Fig. 21) [21]. 

The same procedure was used to generate perfluoro-a-naphthalenium ion ... 

CH3 (3.1-3.6) and 2-CH3 (2.S-3.2 ppm). The introduction of a CH3 group to 4-position was observed to cause a down-field shift of the H signal by 0.5 ppm The spin-spin coupling constants for the protonated ring of 1-H-naphthalenium ions have the following values ... 

The influence of the position of CHj groups on the relative stability of methyl-naphthalenium ions is discussed in Sect. IV.2C. 

Ill Structure of Arenium Ions According to Physical Data Table 7. PMR Data of Methyl-substituted 1-Naphthalenium Ions... 

For the rotation hindrance of the methoxy group in 2-halogen-4-methoxybenze-nium ions see in 2-methoxy-l-naphthalenium ion The hindrance of rotation in hydroxyarenium ions was observed in 4-hydroxy-benzenium heptabromodialuminate >. In the PMR spectrum of a solution of this salt in CSj at —70 °C the Hj and Hj atoms give separate signals which coalesce when the temperature rises to —60 °C. 

Table 13. PMR Data of l-Hydroxy-2-Naphthalenium Ions and their O-Derivatives...

Table 15. PMR Data of 4-Hydroxy-1-Naphthalenium Ions and their 0-Derivatives...

Among the 2-naphthalenium ions NMR- C data are available for the 1,2,2,3,4-pentamethyl-substituted cation and for a few hydroxynaphthalenium ions... 

For p-, m- and a-fluorine-substituted ions of Iwnzyl type, 4-fluorine-substituted benzenium, 1,2,3,5,6-pentamethylbenzenium and 1-naphthalenium ions a similar dependence has been established... 

The NMR- F spectroscopy has been used to investigate the polyfluorinated I-naphthalenium ions 12. 0.238,239,413,414) Examples are the chemical shifts of the... 

Table 36. Absorption Spectra of Naphthalenium and Anthracenium Ions (25 °Q...

However, other explanations of the reactions observed are not precluded. Thus, for polyfluorinated arenium ions a preliminary conversion of the ions into radical cations of the respective aromatic structures is discussed. Indeed, the radical cation of octafluoronaphthalene reacts with pentafluorobenzene to yield the same products as the perfluoro-a-naphthalenium ion does. 

The benzbicyclo[3.1.0]hexenyl cation converts into the 1-H-naphthalenium ion at -50 °C in HSO3F-SO2CIF... 

NMR spectra have been recorded for l-X-l,2-dimethyl-3,4,5,6-tetrafluoro- and -tetrachlorobenzenium ions (X=H Cl ) l-(X-phenyl)-l,3,4,5,6-pentamethyl-2-hydroxy- and l-(X-phenyl)-l,2,3,5,6-pentamethyl-4-hydroxyl nzenium ions isomeric tri- and tetramethvl-l-H-naphthalenium ions 2- and 4-p-chloroethyl-1-H-naphthalenium ions oc-naphtonium ions of the (167) type 2- and 3-sub-... 

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