Factors Influencing the Basicities of Triarylcarbinols. The Synthesis of Sesquixanthydrol

Martin, J. C.; Smith, Russell G.

doi:10.1021/ja01065a030

Cited by 135 publications

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“…In aqueous solutions, the tropylium (pKR+ = 4.76 (16)) and xanthylium (pKR+ = -0.83 (19)) cations exist in equilibrium with their hydroxide adducts (5 and 6, respectively). The alcohols 5 and 6 are the predominant species present in most of the reactions in the current study, although the tropylium cation is the major species in the most acidic solutions investigated for the reaction with MAH.…”

Section: Resultsmentioning

confidence: 99%

“…Thirdly, we wished to choose cations that might be expected to be more reactive than the cations investigated to date. Because the tropylium (16) and xanthylium (19) considerably lower than any of the nitrogen heterocyclic cations previously studied, they should fulfill this third criterion since linear free energy relationships between the second-order rate constant for reduction and pKR+ have been established for other series of cations (18,20,21). Fourthly, the xanthylium cation is an attractive acceptor, since it is T-isoelectronic with the acridinium cations that have been the subjects of numerous investigations in this area.…”

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Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Bunting¹,

Conn²

1990

Can. J. Chem.

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, 537 (1990). The pH-dependences of the apparent second-order rate constants (k2PP) for the reduction of 2,4,6-cycloheptatrien-1-01 and 9-xanthydrol by each of 1-benzyl-1,4-dihydronicotinamide (BNH) and 10-methyl-9,lO-dihydroacridine (MAH) have been measured in 20% acetonitrile -80% water, at 25OC and ionic strength 1.0. For each of these reactions, the pH-dependence of kyp is only consistent with reduction occurring via the aromatic cation (either tropyliurn or xanthylium) that is present in equilibrium with these alcoholic species. The relative second-order rate constants (k2BNH/kYAH) for reductions by these two reducing agents (1700 for tropylium and 770 for xanthyliurn) are similar for these two cations. These ratios are also similar to those observed for a variety of nitrogen heteroarornatic hydride acceptors, even though the absolute magnitudes of these rate constants vary by 10''-fold. The second-order rate constants for the reductions of the tropyliurn and xanthyliurn cations are predicted reasonably well by their pKR+ values, with the latter cation being (7 x lo5)-fold more reactive than its T-isoelectronic N-methyl acridiniurn cation. The xanthyliurn cation has the greatest k!NH/koH ratio yet observed for any heteroarornatic cation, and this value further extends the known range of this ratio as a function of reactivity.Key words: hydride transfer, kinetics of reduction, 1,4-dihydropyridine derivatives, tropyliurn cation, xanthyliurn cation. 537 (1990). Operant h 25°C et a une force ionique de 1,0, dans des solutions contenant 20% d'acetonitrile et 80% d'eau, on a mesure la relation qui existe entre le pH et les constantes apparentes de vitesse du deuxikrne ordre (kyp) pour la reduction du cyclohepta-2,4,6-trikn-1-01 et du xanthydr-9-01 soit par le I-benzyl-l,4-dihydronicotinamide (BNH) ou par la 10-methyl-9,10-dihydroacridine (MAH). Pour chacune de ces reactions, la relation entre le pH et le kyP ne correspond qu'h celle attendue pour une reduction se produisant par le biais d'un cation aromatique (soit tropyliurn ou xanthylium) qui est present l'equilibre dans ces espkces alcooliques. Les constantes relatives des vitesses de reaction du second ordre (k2BNH/kyAH) pour les reductions par ces deux agents riducteurs (1700 pour le tropyliurn et 770 pour le xanthyliurn) sont sernblables pour ces deux cations. MCme si les valeurs absolues de ces constantes de vitesse varient par des facteurs allant jusqu'h 101°, ces rapports sont aussi similaires h ceux observes pour un grand nornbre de derives hCtCroaromatiques azotks accepteurs d'hydrure. Utilisant les valeurs des pKR+ des cations, on peut aussi predire assez correcternent les constantes de vitesse du deuxikrne ordre pour les reductions des cations tropyliurn et xanthylium; ce dernier cation est environ 7 X lo5 fois plus rkactif que le cation N-methyl acridinium qui lui est T-isoelectronique. La valeur du rapport k!NH/koH du cation xanthyliurn est la plus ClevCe avoir Ct C observee jusqu'h rnaintenant et cette valeur Clargit la plage connue de ce rapport ...

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Bunting¹,

Conn²

1990

Can. J. Chem.

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“…Crystals of the tetrafluoroborate salt of the tris(2,6-dimethoxyphenyl)methyl cation (2) were first prepared by oxidizing (3) in the presence of lithium tetrafluoroborate (Kahr & Jackson, 1985). They were later obtained in a more straightforward manner by treating tris-(2,6-dimethoxyphenyl)methanol (Martin & Smith, 1964) in 10% H2504 with a 48% solution of HBF4. The resulting metallic green precipitate was filtered and recrystallized from acetone to give thin plates.…”

Section: Methodsmentioning

confidence: 99%

Comparison of twists in isosteric propellers: X-ray structures of tris(2,6-dimethoxyphenyl)borane, tris(2,6-dimethoxyphenyl)methyl cation and tris(2,6-dimethoxyphenyl)methyl radical

Kahr¹,

Jackson²,

Ward³

et al. 1992

Acta Crystallogr Sect B

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324TETRAETHYLTHIURAM DISULFIDE those from the refinements including up to hexadecapole terms and -0.2 (octapole +) for S1]. This may be the result of correlations among the coefficients of multipole terms, Plm, and the thermal parameters, Uo..Thanks are due to the National Science Council of ROC for financial support.References FABIUS, B., COHEN-ADDAD, C., LARSEN, F. K., LEI-IMANN, M. S. & BECKER, P. (1989). J. Am. Chem. Soc. 111, 5728-5732. GLEITER, R. & HOFFMANN, R. (1968). Tetrahedron, 24, 5899-5911. HANSEN, N. K. & COPPENS, P. (1978). Acta Cryst. A34, 909-921.HOWELL, J., ROSSI, A., WALLACE, D., HARAra, K. & HOFFMANN, R. (1977 AbstractThe X-ray structures of three per-o-methoxytriphenyl-X molecules were determined by direct methods. Tris(2,6-dimethoxyphenyl)borane (1), C24H27BO6, Mr=422.3, monoclinic, C2/e, a = 11.076(5), b=20.839(8), c=9.944(4) A, /3= 98.40 (3) °, V = 2271 (1) ]k 3, Z = 4, Dx = 1.24 gcm -3, A(Mo Ka) = 0.71073 A, ~ = 0.8 cm-1, F(000) = 896, T=295K.Refinement based on 926 unique observed reflections and 170 parameters gave a final R(Fo)=0.045. The tetrafluoroborate salt of the isoelectronic tris(2,6-dimethoxyphenyl)methyl cation (2), CEsH270~.BF4, Mr = 510.3, triclinic, P1, a = 7.214(5), b= 12.931 (4), c = 13.633 (3)A, a = 83.13 (2), /3 = 77.70 (3), y = 80.56 (4) °, v= 0108-7681/92/030324-06506.001221 (1)/~3, Z = 2, Dx = 1.39 g cm -3, a(Cu Ka) = 1.5418 A, br = 9.7 cm-1, F(000) = 532, T= 110 K. Refinement based on 2393 unique observed reflections and 325 parameters gave a final R(Fo) = 0.056. Tris(2,6-dimethoxyphenyl)methyl radical (3), C25H2706, Mr = 423.5, monoclinic, P2/n, a = 10.405(1), b=9.429(2), c=11.767(2)A, /3= 102.120 (9) °, V = 1128.7 (6) A 3, Z = 2, Dx = 1.25 g cm -3, ,~(Mo Ka) = 0.71073/~, /x = 0.8 cm -1, F(000) = 450, T = 295 K. Refinement based on 1189 unique observed reflections and 142 parameters gave a final R(Fo)= 0.059. The borane (1) adopts an approximate D 3 conformation in the lattice at a site with crystallographic (72 symmetry and aryl twist angles of 62.8 (2) and 64.18 (2) ° for the special and general rings. The cation (2) adopts a general posi-© 1992 International Union of Crystallography KAHR, JACKSON, WARD, JANG AND BLOUNT 325 Table 1. Crystal structure determination and refinement data for tris (2,6-dimethoxyphenyl)tris (2,6-dimethoxyphenyl)methyl cation (2) and tris (2,6-dimethoxyphenyl) tion in the lattice with approximate C2 symmetry. The aryl twist angles are 32.6(2), 46.1 (2) and 48.9 (2) °. The free radical (3) adopts a conformation that deviates markedly from the expected groundstate structure; the special ring on a crystallographic C2 axis is twisted out of the plane of coordination by only 12.3 (5) ° while the general rings are twisted by 61.0(1) ° . IntroductionSingle-crystal structure determinations of tris-(2,6-dimethoxyphenyl)borane (1), tris(2,6-dimethoxyphenyl)methyl cation (2) and tris(2,6-dimethoxyphenyl)methyl radical (3) were undertaken to characterize the shape of the nucleophilic pocket formed by a tripod of methoxy groups that shield th...

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“…[1][2][3][4][5][6][7][8][9][10][11][12][13] These compounds are of great fundamental interest and yet they also have a range of potential applications in photochemistry, 14,15 synthesis, 16,17 materials science, 18-21 spintronics [22][23][24] and biology. 25,26 In particular, open-shell polycyclic aromatic hydrocarbons have been shown to be promising molecular conductors and spin carriers in the emerging field of organic spin chemistry.…”

Section: Introductionmentioning

confidence: 99%

Electronically Stabilized Nonplanar Phenalenyl Radical and Its Planar Isomer

et al. 2015

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Stable phenalenyl radicals have great potential as the basis for new materials for applications in the field of molecular electronics. In particular, electronically stabilized phenalenyl species that do not require steric shielding are molecules of fundamental interest, but are notoriously difficult to synthesize. Herein, the synthesis and characterization of two phenalenyl type cations is reported: planar benzo[i]naphtho[2,1,8-mna]xanthenium (8 + ) and helical benzo[a]naphtha-[8,1,2-jkl]xanthenium (9 + ) which can be reduced to the corresponding radicals. Radical 9 represents the first stable, helical phenalenyl radical which does not rely on bulky substituents to ensure its stability. Both cations are water-soluble and the radicals are stable for weeks at room temperature under air. These compounds were characterized crystallographically, and also by NMR, EPR, electrochemistry and electronic spectra. The synthesis of the previously reported compound benzo [5,6]naphthaceno[1,12,11,10-jklmna]xanthylium (5 + ), the largest oxygen-containing polycyclic hydrocarbon, was undertaken for comparison with 8 + and 9 + , allowing us to report its crystal structure here for the first time. The different properties of these compounds and their radicals are explained by considering their differing aromaticities using in-depth computational methods.

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Factors Influencing the Basicities of Triarylcarbinols. The Synthesis of Sesquixanthydrol

Cited by 135 publications

References 0 publications

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Kinetics of the reduction of the tropylium and xanthylium cations by 1,4-dihydropyridine derivatives

Comparison of twists in isosteric propellers: X-ray structures of tris(2,6-dimethoxyphenyl)borane, tris(2,6-dimethoxyphenyl)methyl cation and tris(2,6-dimethoxyphenyl)methyl radical

Electronically Stabilized Nonplanar Phenalenyl Radical and Its Planar Isomer

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