Electrophilic Aromatic Substitution in Naphthalene

Naphthalene ean undergo electrophilie substitution reactions analogous to those of benzene. Two different products can be obtained, e.g., for nitration. 

One way to anticipate the favored product is to consider the shape of naphthalene s best electron-donor orbital, the highest-occupied molecular orbital (HOMO). Display the HOMO in naphthalene and identify the sites most suitable for electrophilic attack. Which substitution product is predicted by an orbital-control mechanism Ts this the experimental result  

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  

The HOMO of naphthalene reveals the likely site of electrophilic attack. 

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A review of solvent properties of, and organic reactivity in, ionic liquids demonstrates the relatively small number of quantitative studies of electrophilic aromatic substitution in these media.3 Studies mentioned in the review indicate conventional polar mechanisms. 1-Methylpyrrole reacts with acyl chlorides in the ionic liquid 1-butylpyridinium tetrafluoroborate to form the corresponding 2-acylpyrrole in the presence of a catalytic amount of ytterbium(III) trifluoromethanesulfonate.4 The ionic liquid-catalyst system is recyclable. Chloroindate(III) ionic liquids5 are catalytic media for the acylation, using acid chlorides and anhydrides, of naphthalene, benzene, and various substituted benzenes at 80-120 °C. Again the ionic liquid is recyclable. 

In addition to benzene and naphthalene derivatives, heteroaromatic compounds such as ferrocene[232, furan, thiophene, selenophene[233,234], and cyclobutadiene iron carbonyl complexpSS] react with alkenes to give vinyl heterocydes. The ease of the reaction of styrene with sub.stituted benzenes to give stilbene derivatives 260 increases in the order benzene < naphthalene < ferrocene < furan. The effect of substituents in this reaction is similar to that in the electrophilic aromatic substitution reactions[236]. 

Polycyclic aromatic hydrocarbons undergo electrophilic aromatic substitution when treated with the same reagents that react with benzene In general polycyclic aromatic hydrocarbons are more reactive than benzene Most lack the symmetry of benzene how ever and mixtures of products may be formed even on monosubstitution Among poly cyclic aromatic hydrocarbons we will discuss only naphthalene and that only briefly Two sites are available for substitution m naphthalene C 1 and C 2 C 1 being normally the preferred site of electrophilic attack... 

The polycyclic aromatic hydrocarbons such as naphthalene, anthracene, and phenan-threne undergo electrophilic aromatic substitution and are generally more reactive than benzene. One reason is that the activation energy for formation of the c-complex is lower than for benzene because more of the initial resonance stabilization is retained in intermediates that have a fused benzene ring. 

The y-nitrogen atom of a sulfonic acid azide is electrophilic and reacts in an electrophilic aromatic substitution with an activated benzene or naphthalene derivative, e.g., a phenoxide ion, forming a l-tosyl-3-aryltriazene (2.47). The 1,4-quinone diazide is obtained by hydrolysis (Scheme 2-30, Tedder and Webster, 1960). The general applicability of this reaction seems to be doubtful. With 1-naphthol the 1,2-naphthoquinone diazide was obtained, not the 1,4-isomer. 

The quantum-chemical calculation of charge-transfer states as possible intermediates in electrophilic aromatic substitution reactions, making allowance for solvation effects, has been reviewed.6 It has been shown that a simple scaled Hartree-Fock ab initio model describes the ring proton affinity of some polysubstituted benzenes, naphthalenes, biphenylenes, and large alternant aromatics, in agreement with experimental values. The simple additivity rule observed previously in smaller... 

Polycyclic aromatic compounds also undergo electrophilic aromatic substitution reactions. Because the aromatic resonance energy that is lost in forming the arenium ion is lower, these compounds tend to be more reactive than benzene. For example, the brotni-nation of naphthalene, like that of other reactive aromatic compounds, does not require a Lewis acid catalyst ... 

Naphthalene undergoes electrophilic aromatic substitution at C-1 more easily than at C-2. There is a smaller loss of resonance energy in forming the intermediate for reaction at C-1 and reaction takes place more rapidly at this centre. However, the products of aromatic substitution at C-1 suffer interactions with C-8 (peri interactions) and are less stable than the corresponding products of substitution at C-2. Hence those aromatic substitution reactions that are carried out under conditions that allow equilibration between isomers (thermodynamic control) lead to substitution ai C-2, but reactions that are carried out under conditions... 

The major products of further substitution in a monosubstituted naphthalene can usually be predicted by the following rules. As we shall see, these rules are reasonable ones in light of structural theory and our understanding of electrophilic aromatic substitution. 

This reaction was introduced in Section 4.6, Electrophilic Substitution at a Trigonal Planar Center. The electrophile adds to the pi bond of the aromatic ring, path Ag, followed by deprotonation of the cation formed, path Dg, restoring aromatic stabilization. See Section 5.6 Aromatic Rings, for a discussion of electrophilic aromatic substitution on heteroaromatics like pyridine and on condensed aromatics like naphthalene. 

Also like benzene, naphthalene undergoes electrophilic aromatic substitution reactions. Substitution occurs preferentially at the 1-position. In common nomenclature, the 1-position is called the a-position and the 2-position is called the j8-position. 

Electrophilic aromatic substitution is the most traditional method for introducing functional groups into an aromatic ring. Lack of complete regioselectivity produces mixtures of compounds, however. Microwave irradiation has been used to modify and invert the selectivity of these reactions. In the sulfonation of naphthalene (24) under microwave irradiation, Stuerga [50] showed that the ratio of 1- and 2-naphthalenesulfonic acids (1- and 2-NSA, 25 and 26) obtained is a function of the applied power (Fig. 5.16). 

Thermal treatment of the dimer with anisole, toluene, and 1-chloronaphtha-lene in the presence of a large excess of pTsOH and air leads to the formation of mono-arylated azafullerenes in 78-90% isolated yields [68]. The reaction with anisole and toluene yield para-substitution products 35 and 39, while 1-chloro-naphthalene is substituted at various positions (Fig. 21). The reaction does not take place in the absence of air or pTsOH. The reaction is presumed to proceed through electrophilic aromatic substitution by C59N, which was proposed as being formed via thermal homolysis of the dimer, followed by oxidation with O2. 

We introduced you to the 10-electron aromatic system of naphthalene in Chapter 7. As you would expect, it undergoes electrophilic aromatic substitution with the same reagents you met in Chapter 21, but the regioselectivity of its reactions is of a different type to the ortho, meta,... 

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