A-Naphthylmethyl anion

Fig. 2. Calculated change in HOMO-LUMO splitting of heterocycles isoconjugate with the a-naphthylmethyl anion vs frequency of their first n -> r absorption band in (i) ethanol ( ) or (ii) water buffered at pH 10 (O).

Suppose that the free energy difference between these heterocycles (Table VI) and their conjugate acids can be equated to a constant term, which represents the dissociation energy of the OH bond (AEoh) plus the difference in the total n-bond energies of the two species (A ). For convenience, we will restrict attention to heterocycles isoelectronic with the a-naphthylmethyl anion. The equilibrium 436 437 is a representative example. 

The stereoisomerization of the cyclopropanes 178 via dianions 180" (Scheme 18) is also rigorously excluded. A priori, this is not a totally unlikely pathway since Lagendijk and Szwarc have deduced from kinetics that it is the dianion that breaks the C-C bond in the reaction of electron sources with 1,2-di-a-naphthylethane to give a-naphthylmethyl anions. Similarly, Grovenstein and coworkers have recently found that bond cleavage in the reaction of 1,2-di-p-tolylethane with Cs/K/Na alloy occurs at the dianion stage. 

FIGURE 3.26. Distribution of formal charge (a) in the a-naphthylmethyl anion (b) in a-naphthylamine. 

Equation (4.94) can be used to predict quantitatively the effect of heteroatoms in different positions in a given system. One can, for example, predict from the distribution of formal charge in the a-naphthylmethyl anion (21) that heteroatoms should have a greater effect in the ring carrying the exo-cyclic group. Thus the methyl groups in 1-methylisoquinoline (22) and... 

Benzimidazoles, too, are readily alkylated either in neutral or basic medium. As with the uncondensed compounds, the former conditions are complicated by salt formation, but to a lesser extent since benzimidazoles are less basic. It is often valuable to vary the initial amounts of alkali and alkyl halide in order to improve yields. The best yields of 1-alkylbenzimidazole (76-83% for primary and 50-60% for secondary alkyl and aralkyl bromides) result with two moles of bromide and 1.5 moles of alkali per mole of benzimidazole (66RCRI22). There is severe steric hindrance to the alkylation of 2-arylben-zimidazoles in alkaline medium, but reactions with the silver salts seem more successful. The rapid and almost quantitative reaction between a benzimidazole and dimethylphenyl-alkylammonium chlorides in aqueous sodium hydroxide provides a very convenient method of introducing a primary aralkyl group (benzyl, a-naphthylmethyl). There has been little systematic study of the dkylation of unsymmetrical benzimidazoles, though much the same criteria should apply as in the uncondensed compounds. In this respect the observation that 1-bromopropane reacts with the anion of 2,6-dimethyl-4-nitrobenzimidazole to give... 

A related biphasic synthesis uses [Co(CO)4] as the catalyst, but in this case the reaction is limited to substrates such as benzyl and naphthylmethyl halides which are susceptible to attack by the metal carbonyl anion. ... 

In later work it was shown that water-soluble antennas could be made by copolymerizing aa oinatic monomers such as vinyl naphthalene and naphthylmethyl methacrylate with polyelectrolytes such as acrylic acid [3,4]. The high efficiency of these antennas in dilute aqueous base was attributed to the hypercoiling of the poly-(acrylic acid) chain to give a pseudo micellar stincture such as that illustrated schematically in Figure 2. We believe that such structures are formed spontaneously in solution due to the hydro-phobic interactions of the large aromatic ccmiponents stabilized by the interaction of water with the hydrophillic carboxyl anions. 

The photochemical cleavage of naphthylmethyl alkanoates in methanol is reported to proceed by homolytic cleavage to naphthylmethyl radical and acyloxy radical,the latter decarboxylates in competition with electron transfer to give naphthylmethyl cation and carboxylate anion. Using known rates of electron transfer as a clock the rate constants for decarboxylation of the acyloxy radicals has been estimated.The light induced homolysis of 1-chloromethyl-naphthalene has also been studied using chemically induced dynamic electron polarisation (CIDEP) spectroscopy to detect the naphthyl-... 

---