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PubMed2005

1,2-Dicarba-closo-dodecaboran-1-yl naphthalene derivatives.

1,2-Dicarba-closo-dodecaboranes (o-carboranes) and naphthalenes have potential value as components or building blocks for supramolecular systems. We have efficiently synthesized 1-(1,2-dicarba-closo-dodecaboran-1-yl)naphthalene and 2-(1,2-dicarba-closo-dodecaboran-1-yl)naphthalene derivatives by employing three preparative methods: cyclization of the corresponding acetylenes with decaborane(14), an Ullmann-type coupling reaction of carboranes with aryl halide, and the aromatic nucleophilic substitution (S(N)Ar) reaction of aryl-o-carboranes with nitrophenyl halide. The optimum conditions of each method for synthesis of the title compounds were also investigated.

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PubMed2002

Protonated benzofuran, anthracene, naphthalene, benzene, ethene, and ethyne: measurements and estimates of pK(a) and pK(R).

Aqueous solvolyses of acyl derivatives of hydrates (water adducts) of anthracene and benzofuran yield carbocations which undergo competitive deprotonation to form the aromatic molecules and nucleophilic reaction with water to give the aromatic hydrates. Trapping experiments with azide ions yield rate constants k(p) for the deprotonation and k(H2O) for the nucleophilic reaction based on the "azide clock". Combining these with rate constants for (a) the H(+)-catalyzed reaction of the hydrate to form the carbocation and (b) hydrogen isotope exchange of the aromatic molecule (from the literature) yields pK(R) = -6.0 and -9.4 and pK(a) = -13.5 and -16.3 for the protonated anthracene and protonated benzofuran, respectively. These pK values may be compared with pK(R) = -6.7 for naphthalene hydrate (1-hydroxy-1,2-dihydronaphthalene), extrapolated to water from measurements by Pirinccioglu and Thibblin for acetonitrile-water mixtures, and pK(a) = -20.4 for the 2-protonated naphthalene from combining k(p) with an exchange rate constant. The differences between pK(R) and pK(a) correspond to pK(H2O), the equilibrium constant for hydration of the aromatic molecule (pK(H2O) = pK(R) - pK(a)). For naphthalene and anthracene values of pK(H2O) = +13.7 and +7.5 compare with independent estimates of +14.2 and +7.4. For benzene, pK(a) = -24.3 is derived from an exchange rate constant and an assigned value for the reverse rate constant close to the limit for solvent relaxation. Combining this pK(a) with calculated values of pK(H2O) gives pK(R) = -2.4 and -2.1 for protonated benzenes forming 1,2- and 1,4-hydrates, respectively. Coincidentally, the rate constant for protonation of benzene is similar to those for protonation of ethylene and acetylene (Lucchini, V.; Modena, G. J. Am. Chem Soc. 1990, 112, 6291). Values of pK(a) for the ethyl and vinyl cations (-24.8) may thus be derived in the same way as that for the benzenonium ion. Combining these with appropriate values of pK(H2O) then yields pK(R) = -39.8 and -29.6 for the vinyl and ethyl cations, respectively.

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PubMed2002

Tris(eta4-naphthalene)- and tris(1-4-eta4-anthracene)tantalate(1-): first homoleptic arene complexes of anionic tantalum.

Reduction of tantalum pentachloride by 6 equiv of sodium naphthalene in 1,2-dimethoxyethane provided, after recrystallization from tetrahydrofuran, 50-55% yields of yellow, pyrophoric [Na(THF)][Ta(C10H8)3]. The product was shown by 1H and 13C NMR spectra and an X-ray study (on the corresponding [Na(crypt 2.2.2)]salt) to be tris(eta4-naphthalene)tantalate(1-), 1, the first homoleptic naphthalene complex of a third row (5d) transition metal. Salts of 1 react under mild conditions with excess CO (1 atm pressure, -60 degrees to +20 degrees C) and 3 equiv of anthracene, C14H10 (20 degrees C), to give 99 and 52% yields of yellow [Ta(CO)6]- and orange [Ta(C14H10)3]-, (2), respectively. The latter is the first homoleptic anthracene complex of a group 5 element and only the third one known, the others being Cr(eta6-C14H10)2 and [Co(eta4-C14H10)2]-. NMR spectra and X-ray structural characterization, as the [Na(crypt 2.2.2)] salt, established 2 to be [Ta(1-4-eta4-C14H10)3]- and is very similar to 1 in solution and in the solid state. Salts of 2 also undergo facile ligand substitution reactions. For example, it reacts with 1,3,5,7-cyclooctatetraene, COT, at 20 degrees in THF to give high yields of the previously known [Ta(COT)3]-, which was structurally characterized as the Na(crypt 2.2.2)salt. One particularly important feature concerning 1 and 2 is that they are the first available synthons for "naked" atomic Ta- and promise to be useful reagents for the general exploration of low-valent tantalum chemistry. Also, 1 and 2 represent the first homoleptic arene tantalum complexes to have been prepared by conventional syntheses. The only previously known substance of this class is the neutral bis(benzene)tantalum(0), which was accessed by the co-condensation of atomic tantalum and benzene vapor in a sophisticated (electron-gun furnace equipped) metal atom reactor.

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PubMed2002

Diuranium inverted sandwiches involving naphthalene and cyclooctatetraene.

Treatment of IU(DME)(NC[(t)Bu]Mes)(3) (2-I-DME) with 4 equiv of KC(8) and 0.5 equiv of naphthalene in DME allowed the isolation of a naphthalene-bridged compound, K(2)(mu-eta(6),eta(6)-C(10)H(8))[U(NC[(t)Bu]Mes)(3)](2) (K(2)-2(2)-mu-C(10)H(8)), in 60% yield as a dark brown powder. The twelve U-C distances are rather short, varying from 2.565(11) to 2.749(10) A. Treatment of M(2)-2(2)-mu-C(10)H(8) (M = Na, K) with 2 equiv of 1,3,5,7-cyclooctatetraene afforded a mixture of two products: M-2-COT and 2(2)-mu-COT. Compound 2(2)-mu-COT can be assembled independently in 90% yield by salt elimination upon reaction of M-2-COT with iodide 2-I-DME. The U-C(arene) distance in compound 2(2)-mu-COT is longer than that in its naphthalene counterpart K(2)-2(2)-mu-C(10)H(8)(2.822 vs 2.634 A), in accord with bonding considerations. A DFT study performed on model compounds for both M(2)-2(2)-mu-C(10)H(8) and 2(2)-mu-COT indicates that the delta bonds present in the former compound show better covalent overlap.

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PubMed2003

The azulene-to-naphthalene rearrangement revisited: a DFT study of intramolecular and radical-promoted mechanisms.

Intramolecular and radical-promoted mechanisms for the rearrangement of azulene to naphthalene are assessed with the aid of density functional calculations. All intramolecular mechanisms have very high activation energies (>/=350 kJ mol(-1) from azulene) and so can only be competitive at temperatures above 1000 degrees C. Two radical-promoted mechanisms, the methylene walk and spiran pathways, dominate the reaction below this temperature. The activation energy for an orbital symmetry-allowed mechanism via a bicyclobutane intermediate is 382 kJ mol(-1). The norcaradiene-vinylidene mechanism that has been proposed in order to explain the formation of small amounts of 1-phenyl-1-buten-3-ynes from flash thermolysis of azulene has an activation energy of 360 kJ mol(-1); subtle features of the B3LYP/6-31G(d) energy surface for this mechanism are discussed. All intermediates and transition states on the spiran and methylene walk radical-promoted pathways have been located at the B3LYP/6-31G(d) level. Interconversion of all n-H-azulyl radicals via hydrogen shifts was also examined, and hydrogen shifts around the five-membered ring are competitive with the mechanisms leading to rearrangement to naphthalene, but those around the seven-membered ring are not. Conversion of a tricyclic radical to the 9-H-naphthyl radical is the rate-limiting transition state on the spiran pathway, and lies 164.0 kJ mol(-1) above that of the 1-H-azulyl radical. The transition state for the degenerate hydrogen shift between the 9-H-azulyl and 10-H-azulyl radicals is 7.4 kJ mol(-1) lower. Partial equilibration of the intermediates in the spiran pathway via this shift may therefore occur, and this can account for the surprising formation of 1-methylnaphthalene from 2-methylazulene. The rate-limiting transition state for the methylene walk pathway involves the concerted transfer of a methylene group from one ring to the other and lies 182.3 kJ mol(-1) above that of the 1-H-azulyl radical. It is shown that rearrangement via a combination of 31% methylene walk and 69% spiran pathways can account semiquantitatively for all the products from 1-(13)C-azulene, 9-(13)C-azulene, and 4,7-(13)C(2)-azulene, in addition to accounting for the products from methylazulenes, and the formation of naphthalene-d(0) and -d(2) from azulene-4-d. It is also pointed out that a small extension to the spiran pathway could provide an alternative explanation for the formation of 1-phenyl-1-buten-3-ynes.

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PubMed2004

Insignificance of P-H...P hydrogen bonding: structural chemistry of neutral and protonated 1,8-di(phosphinyl)naphthalene.

While there is extensive information on 1,8-di(amino)naphthalene (i.e., the parent compound of the "proton sponge" series), the corresponding phosphorus compound has not been described. A high-yield synthesis of 1,8-di(phosphinyl)naphthalene (9) and the 1-naphthylphosphine reference compound (4) is now reported. Thermal decomposition of 9 leads to intramolecular dehydrogenative P-P coupling to afford 1,2-dihydro-1,2-diphosphaacenaphthene (10). Protonation of 9 and 4 with CF(3)SO(3)H gives quantitative yields of the monophosphonium salts 11 and 5, respectively. With excess acid and traces of moisture, the hydronium salt [C(10)H(6)(PH(2))(PH(3))](+)[H(3)O](+)2[CF(3)SO(3)](-) (13) is obtained. The structures of 9, 11, and 13 have been determined. Molecules of 9 have a planar naphthalene skeleton, C(10)H(6)P(2), with the two -PH(2) groups in a transoid conformation. The molecules form loose dimers in the crystal, the individual chiral enantiomers of which are related by a center of inversion. In contrast to the situation for the amino analogue, and despite the proximity of the two -PH(2) functions, there is no intra- or intermolecular hydrogen bonding. Solutions of 9 (in CD(2)Cl(2)) show equivalent P-bound hydrogen atoms due to conformational fluctionality. By analysis of the ABCD(2)XX'D'(2)C'B'A' spin system, it was shown that, in 9, there are strong through-space pericouplings [(n)J(P(X)P(X)(')) = 221.6 Hz, (n)J(P(X)H(D)(')) = 31.7 Hz, (n)J(H(D)H(D)(')) = 3.9 Hz]. In the cations of 11, the C(10)H(6)P(2) skeleton is also planar (by C(s) symmetry), with the -PH(2) and -PH(3)(+) groups in a conformation which rules out any P-H...P hydrogen bonding. The hydronium cation and the two triflate anions in 13 are associated into an anionic network through extensive hydrogen bonding surrounding stacks of the phosphonium cations. In solution, the cations of 11 and 13 show separate (31)P resonances for the two phosphorus atoms with fully resolved (1)J(PH) couplings, which indicate that there is no intra- or intercationic proton exchange. By contrast, the NMR spectra of solutions of [C(10)H(6)(NH(2))(NH(3))](+)X(-) salts show proton scrambling equilibrating all five N-bound hydrogen atoms, and in the crystal, the conformations of the cations feature intramolecular N-H...N hydrogen bonding.

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PubMed2004

Stepwise photocleavage of two C-O bonds of 1,8-bis[(4-benzoylphenoxy)-methyl]naphthalene with three-step excitation using three-color, three-laser flash photolysis.

Stepwise photocleavage of two naphthylmethyl-oxygen bonds of 1,8-bis[(4-benzoylphenoxy)methyl]naphthalene (1,8-(BPO-CH2)2Np, 1) was observed during three-color, three-laser flash photolysis at room temperature. The mechanism from 1 to the final product, acenaphthene (2), was clearly elucidated. The first (308 nm, 5 mJ pulse-1) XeCl laser excited 1 to the lowest triplet excited state 1(T1), in which the excited energy was localized in the naphthalene moiety, but the C-O bond cleavage did not occur. The second (430 nm, 7 mJ pulse-1) OPO laser excited 1(T1) to the higher triplet excited states 1(Tn) in which the excited energy is delocalized in the naphthalene moiety and C-O bonds, and one C-O bond cleavage occurred. The third (355 nm, 10 mJ pulse-1) YAG laser excited the carbon-centered radical in the ground state 1-(BPO-CH2)NpCH2*(D0) to its excited states 1-(BPO-CH2)NpCH2*(Dn), from which the second C-O bond cleavage occurred to give 2 as the final product. This is a successful example of stepwise cleavage of two equivalent C-O bonds in a molecule using three-color three-laser photolysis method.

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PubMed2005

1,8-Bis(hexamethyltriaminophosphazenyl)naphthalene, HMPN: a superbasic bisphosphazene "proton sponge".

It is shown that a combination of Schwesinger's phosphazene base concept and the idea of the disubstituted 1,8-naphthalene spacer, first introduced by Alder in paradigmatic 1,8-bis(dimethylamino)naphthalene (DMAN), yields a new superbase, HMPN, which represents the up to date most basic representative of this class of "proton sponges", as evidenced by the theoretically estimated proton affinity PA = 274 kcal/mol and the measured pK(BH+) (MeCN) 29.9 +/- 0.2. HMPN is by nearly 12 orders of magnitude more basic than Alder's classical 1,8-bis(dimethylamino)naphthalene (DMAN). The title compound, HMPN, is prepared and fully characterized. The spatial structure of HMPN and its conjugate acid is determined by X-ray technique and theoretical DFT calculations. It is found that monoprotonated HMPN has an unsymmetrical intramolecular hydrogen bridge (IHB). This cooperative proton chelating effect renders the bisphosphazene more basic than Schwesinger's set of "monodentate" P1 phosphazene bases. The density functional calculations are in good accordance with the experimental results, providing some complementary information. They conclusively show that the high basicity of HMPN is a consequence of the high energy content of the base in its initial neutral state and the intramolecular hydrogen bonding in the resulting conjugate acid with contributions to proton affinity of 14.1 and 9.5 kcal/mol, respectively.

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PubMed2006

Charge-localized naphthalene-bridged bis-hydrazine radical cations.

Electron transfer (ET) in four symmetrically substituted naphthalene-bridged bis-hydrazine radical cations (1,4; 1,5; 2,6; and 2,7) is compared within the Marcus-Hush framework. The ET rate constants (k(ET)) for three of the compounds were measured by ESR; the 2,7-substituted compound has an intramolecular ET that is too slow to measure by this method. The k(ET) values are significantly dependent upon the substitution pattern of the hydrazine units on the naphthalene bridge but do not correlate with the distance between them. This is contrary to an assumption that is frequently made about intervalence compounds that the bridge serves only as a spacer that fixes the distance between the charge-bearing units. The internal vibrational and solvent portions (lambda(v) and lambda(s)) of the total reorganization energy (lambda) have been separated using solvent effects on the intervalence band maximum, resulting in a lambda(v) that is the same, 9900 cm(-1), for the differently substituted naphthalenes. This is in accord with the general assumption that lambda(v) is primarily dependent upon the charge bearing unit and not the bridge. However, the trends in lambda(s) cannot be explained by dielectric continuum theory.

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PubMed2002

Structure of 1-(arylselanyl)naphthalenes. 2. G dependence in 8-G-1-(p-YC(6)H(4)Se)C(10)H(6).

The structures of 8-G-1-(p-YC(6)H(4)Se)C(10)H(6) (1 (G = Cl) and 2 (G = Br): Y = H (a), OMe (b), Me (c), Cl (d), Br (e), COOEt (f), and NO(2) (g)) were investigated by X-ray crystallographic analysis, NMR spectroscopy, and ab initio MO calculations. The structures of all members in 1 and 2 are concluded to be type B, which is in striking contrast to the type A structure for 4d-g (4 (g(n)), where G = H). The Se-C(i) bond of the p-YC(6)H(4)Se group in 8-G-1-(p-YC(6)H(4)Se)C(10)H(6) is almost perpendicular to the naphthyl plane in type A, and it is located on the plane in type B. The chlorine and bromine substitution at the 8-position in 1 and 2 dramatically changes the type A structure of 4 (g(n)) to type B. The nonbonded G- - -Se-C 3c-4e type interaction must contribute to stabilize the type B structure. The type B structure in 1 and 2 should also be more stabilized than the same structure in 4 by the 3c-4e type interaction: The structure of 4b is type B in the crystals and type B would be more stable for 4c and might be for 4a in solutions. Ab initio MO calculations are performed on 8-G-1-(p-YC(6)H(4)Se)C(10)H(6), 8-G-C(10)H(6)SeH-1, and models HG- - -SeH(2), where G = Cl, Br, and F, to clarify the reason for the dramatic change in the structures. The type B structure is optimized to be more stable than the type A for all species examined, which supports the observations. The energy differences between type B and type A are larger for the models than for the naphthalenes. While the superiority of the type B for the former is Br > Cl >> F, that of the latter is Br approximately Cl >/= F. These results show that the main factor of the structural change from type A to type B is the nonbonded G- - -Se-C 3c-4e interaction. The electronic effect of halogens through the naphthalene pi-framework would also contribute to some extent, although the direct comparison of the evaluated values between the naphthalene systems and the models is not so easy. Factors to stabilize the two structures of 1, 2, 4, and 8-(MeSe)-1-(p-YC(6)H(4)Se)C(10)H(6) are reexamined from a viewpoint of the nonbonded G- - -Se-C 3c-4e interaction (G dependence), together with the electronic effect of Y (Y dependence).

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PubMed2002

A convenient preparation of functionalized 1,8-dioxygenated naphthalenes from 6-alkoxybenzocyclobutenones.

An alternate route for the synthesis of naphthalene building blocks 1-4 has been developed, starting from readily available 6-alkoxybenzocyclobutenones. As thermolysis of a propynylbenzocyclobutenol only provided the naphthalene in low yield, allenyl-substituted benzocyclobutenols were investigated. The desired allenic precursors were prepared by a two-step procedure, which involved hydroxyl-directed reduction of the chloropropargylbenzocyclobutenols obtained from addition of lithiopropargyl chloride to the benzocyclobutenones. Thermolysis of the allenic alcohols gave the desired naphthalenes in good yields.

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PubMed2003

Crystal structure and rotational barrier of octakis(bromomethyl)naphthalene.

Octakis(bromomethyl)naphthalene (4) adopts in the crystal a chiral conformation with a helical central naphthalene core and the bromomethyl groups disposed in an alternate up-down "in" arrangement. According to MM3 calculations, this conformation is less stable than the corresponding all alternated "out" form, while B3LYP/LANL2DZ calculations suggest the opposite stability order. The topomerization barrier (16.0 kcal mol(-1)) is ascribed to an enantiomerization process requiring 180 degrees rotation of all the bromomethyl groups and reversal of the helical sense of the naphthalene core.

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PubMed2003

1,8-bis(dimethylethyleneguanidino)naphthalene: tailoring the basicity of bisguanidine "proton sponges" by experiment and theory.

1,8-bis(dimethylethyleneguanidino)naphthalene (DMEGN), the second example of a peralkyl guanidine "proton sponge" based on the 1,8-naphthalene backbone, was prepared and fully characterized. The crystal structure analysis of monoprotonated DMEGN reveals an unsymmetrical intramolecular hydrogen bridge. A decrease in the basicity with respect to the noncyclic parent 1,8-bis(tetramethylguanidino)naphthalene was found. Nevertheless, a new proton sponge provides a new crossbar in the ladder of highly basic neutral organic compounds. A detailed theoretical study of DMEGN and related cyclic guanidines explains this surprising experimental result. Homodesmotic reactions reveal that the intramolecular hydrogen bond contributes effectively 10 kcal/mol to proton affinity of DMEGN.

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PubMed1997

Benzotriazole-Assisted Aromatic Ring Annulation: Efficient and General Syntheses of Polysubstituted Naphthalenes and Phenanthrenes.

(Benzotriazol-1-ylmethyl)benzenes and -naphthalenes 1a-f, easily accessible from benzyl bromides and benzotriazole, readily undergo lithiation and subsequent 1,4-addition to alpha,beta-unsaturated aldehydes and ketones. Intramolecular cyclization of the products, induced by acetic acid-hydrobromic acid or polyphosphoric acid (PPA), followed by simultaneous dehydration and debenzotriazolylation furnishes a wide range of polysubstituted naphthalenes 7a-f and of phenanthrenes 9 and 11 in moderate to good yields in one-pot procedures. If compounds 1 are first lithiated and reacted with electrophiles, the resulting alkylation products undergo similar annulation reactions with alpha,beta-unsaturated carbonyl compounds to provide the more highly substituted naphthalenes 6a,b and phenanthrenes 10a,b in moderate overall yields.

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PubMed1999

Synthesis, X-ray Structure, and Electrochemical Oxidative Coupling Reactions of 1,5- and 2,6-Bis(1,4-dithiafulven-6-yl)naphthalenes.

Novel pi-extended tetrathiafulvalene (TTF) derivatives (12a-c, 13a-c, 15a-c) in which the two 1,3-dithiole units are connected through a naphthalene spacer have been prepared in high yields by Wittig-Horner olefination reaction from dialkoxy-substituted diformylnaphthalenes (11a,b, 14) and differently substituted phosphonate esters (10a-c). The electrochemical study revealed a similar behavior for the novel electron donor molecules (12a-c, 13a-c, 15a-c) regardless of the position of the 1,3-dithiole rings on the naphthalene core. The extended donors undergo an efficient electrooxidation process affording new oligomeric extended TTF species which exhibit lower oxidation potential values than their precursor donors. EPR experiments confirm the presence of the cation radical derived from the oligomeric TTF vinylogues and support an ECE process. The structural study has been carried out by X-ray analysis of 12a and semiempirical PM3 calculations and reveals a distorted geometry from the planarity with the naphthalene moiety forming an angle of approximately 35 degrees with the thiafulvalene rings. A good agreement was found between the experimental and calculated values, thus validating the PM3 method. The chemical oxidation of the synthesized donors (12a-c, 13a-c, 15a-c) with strong electron acceptors give rise to charge transfer complexes (CTC) which were characterized by UV-vis, FTIR, and EPR spectroscopy.

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PubMed2005

Dynamics and energetics of the self-assembly of a hydrophobically modified polyelectrolyte: Naphthalene-labeled poly(acrylic acid).

Steady-state and time-resolved fluorescence studies were performed on aqueous solutions of poly(acrylic acid) hydrophobically modified with two very different levels of naphthalene (Np). It is demonstrated that unique information on association phenomena involving hydrophobe-modifed polymers can be obtained from an extended fluorescence study by using data for a less-modified polymer as a reference. For the more highly modified polymer, the presence of excited-state (as well as ground-state) dimers in addition to monomer emission due to locally excited naphthalene gives evidence for hydrophobic association between naphthalene groups. This association becomes, as expected, much less important at higher pH due to the electrostatic repulsion between different chain segments. However, it is noted that even at high pH there is a significant self-association. The coexistence of static and dynamic quenching phenomena of the Np monomer label was also revealed in the time-resolved fluorescence data. The data are compatible with the existence of two types of monomers and one excimer and suggest that the essential contribution to the monomer emission comes from isolated chromophores, whereas excimer formation arises from both a dynamic route (excited Np chromophores able to produce a dynamic excimer) and a static route (excitation of ground-state Np dimers). At room temperature, the dissociative reaction, excimer-to-monomer, can be neglected, and thus the rate constant for excimer formation and decay could be obtained with and without considering the influence of preformed dimers. Temperature has shown to induce different behavior in the polymer photophysics. In the case of the less-labeled polymer, the decays were found to be single-exponential with the fluorescence lifetime decreasing with increasing temperature. From the temperature dependence of the steady-state fluorescence data, the activation energy for excimer formation and the binding energy of the excimer were evaluated at different pH values, through the Stevens-Ban-type plots of the excimer-to-monomer intensity ratio. With the time-resolved data, measured in the temperature range of 5-60 degrees C, it was possible to extract the intrinsic activation energies for excimer formation. The thermodynamic driving force for the intrapolymeric association was found to be dependent on a balance between hydrophobic and electrostatic interactions, which are dependent on the pH, temperature, and hydrophobic content of the polymer.

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PubMed2000

A cyclic oligophenylene containing two 1,8-naphthalene units bridged by two face-to-face biphenyl linkages exhibiting unusual strain and pi-pi interaction

1,8-[1,8-Naphthalenediylbis(4',4-biphenyldiyl)]naphthalene, a very stable strained cyclophane, has been synthesized in moderate yield using the copper-catalyzed coupling of 1, 8-bis(4-(tributylstannyl)phenyl)naphthalene. The X-ray analysis of the titled compound discloses bent p,p'-biphenylylene chains with splayed naphthalene rings, and the p,p'-biphenylylene chains located face-to-face indicate a fairly strong pi-pi interaction.

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PubMed1981

Nitration of naphthalene and remarks on the mechanism of electrophilic aromatic nitration.

Naphthalene was nitrated with a variety of nitrating agents. Comparison of data with Perrin's electrochemical nitration [Perrin, C. L. (1977) J. Am. Chem. Soc. 99, 5516-5518] shows that nitration of naphthalene gives an alpha-nitronaphthalene to beta-nitronaphthalene ratio that varies between 9 and 29 and is thus not constant. Perrin's data, therefore, are considered to be inconclusive evidence for the proposed one-electron transfer mechanism for the nitration of naphthalene and other reactive aromatics. Moodie and Schoefield [Hoggett, J. G., Moodie, R. B., Penton, J. R. & Schoefield, K. (1971) Nitration and Aromatic Reactivity (Cambridge Univ. Press, London)], as well as Perrin, independently concluded that, in the general scheme of nitration of reactive aromatics, there is the necessity to introduce into the classical Ingold mechanism an additional step involving a distinct intermediate preceding the formation of the Wheland intermediate (sigma complexes). This view coincides with our two-step mechanistic picture [Kuhn, S. J. & Olah, G. A. (1961) J. Am. Chem. Soc. 83, 4564-4571] of the nitronium salt nitration of aromatic hydrocarbons (including benzene and toluene), in which low substrate selectivity but high positional selectivity was found, indicating the independence of substrate from positional selectivity.

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