Synthesis of polymeric supports with spacer-modified triazene linkers: aldol and Grignard reactions of immobilized nortropinone

Four new polymeric supports with 3- and 6-carbon atom spacers and triazene linkers derived from meta- and para-aminophenol were synthesized from commercial Merrifield polymer. The supports could be used for immobilization of secondary amines in SPOS. A new strategy based on the use of diethylamine triazenes as masked precursors for the generation of polymer-supported diazonium ions was used. The performance of the new linkers was tested on Grignard and aldol reactions of solid-phase immobilized nortropinone. The new supports with C₃-T2 linkers gave products with better yields and purities than the classical T2 supports or the supports with the C₆-T2 linkers.     

Tripodal pyrene chromophores for semiconductor sensitization: new footprint design

Large footprint tripodal linkers for metal oxide nanoparticle sensitization, substituted with pyrene as the dye, and three COOR binding groups in para or meta position, were prepared to study the effect of the anchoring group position and of the footprint size on the sensitization processes. Two tripods based on tetraphenylsilane, (1-pyrenyl-4-ethynyl-phenyl)-tris(4-carbomethoxyphenyl-4-ethynyl-phenyl)silane, and (1-pyrenyl-4-ethynyl-phenyl)-tris(4-(4-methoxybenzyloxycarbonyl)phenyl-4-ethynyl-phenyl)silane, decomposed during hydrolysis, while the tetraphenyladamantane derivative, 1-(1-pyrenyl-4-ethynyl-phenyl)-3,5,7-(3-carbomethoxyphenyl-4-ethynyl-phenyl)adamantane, was chemically stable and was readily converted into the corresponding acid and bound to TiO₂ films. The FT-IR-ATR spectrum of 1-(1-pyrenyl-p-ethynyl-phenyl)-3,5,7-(3-carboxyphenyl-4-ethynyl-phenyl)adamantane bound to TiO₂ nanoparticles showed bands characteristic of carboxylate bidentate bonds. The UV-vis absorption and fluorescence emission in THF solution at room temperature were typical of pyrenes substituted with oligophenyleneethynylene linkers.     

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : II. (119Sn-13C) coupling constants and 13C chemical shifts of meta- and para-derivatives

Carbon-13 NMR data are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, RC₆H₄Sn(CH₃)₃, where R = para-N(CH₃)₂, para-OCH₃, para-OC₂H₅, para-CH₃, meta-CH₃, -H, para-F, meta-OCH₃, para-Cl, para-Br, meta-F, meta-Cl and para-Sn(CH₃)₃. In the para-derivatives, correlation coefficients with Hammet σ-constants of greater than ca. 0.9 are obtained with the tin-carbon couplings to methyl, C₁ and C₄ carbons, and with the carbon-13 chemical shifts δ(C(1)). In the meta-derivatives, the couplings |J(Sn-CH₃)|:, |:J(Sn-C(1))|:, |:J(Sn-C(3))|: and |:J(Sn-C(6))|:, and the shifts δ(C(1)) and δ(C(5)) correlate well with Hammett σ. In the para-derivatives, sensitivity to change in substituent falls off C(4) > C(3, 5) > C(1) > C(2, 6) > CH₃ as registered by the δ(C), while in the meta-derivatives δ(C) changes decrease C(3) > C(2), C(4) > C(1) > C(5), C(6) > CH₃. The magnitudes of the tin coupling constants decrease C(1) > CH₃ > C(3, 5) > C(2, 6) > C(4) in the para-derivatives, while in the meta-series the order is C(1) > CH₃ > C(3), C(5) > C(2) > C(6) > C(4). The two sets of one-bond |:J(Sn-CH₃)|: and |:J(Sn-C(1)|: values correspond closely to the 0.25/0.33 ratio of coefficients in the LCAO approach, and are interpreted in terms of s-electron redistributions at the tin atom with change in substituent.     

Structure of 1,4,10,19,25,41-C70(CF3)6, isomer with unique arrangement of addends

A novel isomer of C₇₀(CF₃)₆ has been isolated by HPLC from a mixture prepared by trifluoromethylation of C₇₀ with CF₃COOAg. The X-ray structure revealed an unprecedented arrangement of CF₃ groups forming a p³mp ribbon. This result provides additional evidence of the preferable formation of trifluoromethylated fullerene molecules comprising a single continuous ribbon of edge-sharing para- and meta-C₆(CF₃)₂ hexagons.     

Structure-property relationships for novel wholly aromatic polyamide-hydrazides containing various proportions of para-phenylene and meta-phenylene units: I. Synthesis and characterization

A series of novel wholly aromatic polyamide-hydrazides was synthesized by a low temperature solution polycondensation reaction of either 4-amino-3-hydroxybenzhydrazide or 3-amino-4-hydroxybenzhydrazide with an equimolar amount of either terephthaloyl chloride (TCl), isophthaloyl chloride (ICl), or mixtures of various molar ratios of TCl and ICl in anhydrous N,N-dimethylacetamide (DMAc) as a solvent. Polymer structures were identified by elemental analysis and infrared spectroscopy. All the polymers have the same structural formula except the way of linking phenylene units inside the polymer chain. The content of para- and meta-phenylene moieties was varied within this series so that the changes in the latter were 10 mol % from polymer to polymer, starting from an overall content of 0-100 mol %. The prepared polymers were characterized for their properties in order to acquire clear understanding of the influence exerted by controlled structural variations in these polymers upon some of important properties, such as solubility, intrinsic viscosity, moisture regain, mechanical properties and thermal as well as thermo-oxidative stability. The polymers were readily soluble in several organic polar solvents such as DMAc, N,N-dimethylformamide, dimethyl sulphoxide, N-methyl-2-pyrrolidone and hexamethyl phosphoramide and could be cast into flexible films. Their solubilities were found to increase remarkably with introduction of meta-phenylene moieties into the polymer chains. Their intrinsic viscosities ranged from 0.73 to 4.83 dl g⁻¹ in DMAc at 30 °C and increased with the increase of para-phenylene units content. Mechanical properties of the films produced from these polymers are improved markedly by substitution of para-phenylene units for meta-phenylene units. Thermogravimetric studies revealed that the completely para-oriented type of polymer has better thermal and thermo-oxidative stability relative to that of the other polymers. Moreover, the results reveal that the prepared polymers have a great affinity to water sorption. The hydrophilic character increases as a function of meta-oriented phenylene rings incorporated into the polymer chains.     

Ionic liquid immobilization on carbon nanofibers and zeolites: Catalyst design for the liquid-phase toluene chlorination

The environmental-friendly chlorination reaction of toluene by trichloroisocyanuric acid (TCCA, C₃N₃O₃Cl₃) was investigated applying immobilized ionic liquids (ILs) on different supports. Ionic liquids were grafted either on carbon nanofibers (CNF) or encapsulated in zeolites. Their influence on the chlorination activity as well as on the selectivity in different chlorinated products was studied. An unusually high selectivity toward meta-chlorotoluene was achieved, up to 36%. Hence, the selectivity could be tuned to produce either expected ortho-/para-chlorotoluene or meta-chlorotoluene with a proper support choice.     

Temperature dependent chemical shift change in 4-substituted[2.2.2.2]paracyclophanes

Temperature dependent NMR spectra of 4-substituted tetrakis[2.2.2.2]paracyclophane (4°-PCP) were measured at low temperature. The high field shift at low temperature was remarkable for the protons meta and para to an electron withdrawing and/or bulky substituent. While the chemical shift change was very small for the aromatic protons of 4°-PCP bearing a not so bulky and electron donating substituent. From these observations it is concluded that the rotation or vibration of a benzene bearing an electron withdrawing and/or bulky substituent around C₂-C₃-C₆-C₉ axis was increasingly frozen as the temperature decreased to a more stable “lateral” (or half “lateral”, the intermediary state between “face” and “lateral”⁴) conformation, in an interesting contrast to the favored face conformation of unsubstituted 4°-PCP at low temperature as well as at room temperature.     

Pulsed fourier transform NMR of substituted aryltrimethyltin derivatives : III. Proton data at 100 MHz and the derived Hammett σ-constant of the trimethyltin group

Proton NMR data at 100 MHz are reported for thirteen para- and meta-substituted phenyltrimethyltin compounds, XC₆H₄Sn(CH₃)₃, where X = para-N(CH₃)₂, para-OCH₃, para-OC₂H₅, para-CH₃, meta-CH₃, -H, para-F, meta-OCH₃, para-Cl, para-Br, meta-F, meta-Cl and para-Sn(CH₃)₃. Correlation coefficients with Hammett σ-constants of greater than 0.95 are obtained with the methyltin proton chemical shifts and coupling constants to carbon [¹J(¹³C¹H)] and tin [²J(SnC¹H)]. Solvent effects and other extraneous factors invalidate comparisons of ? values in terms of the relative attenuation of the transmission of substituent effects through homologous carbon, silicon, germanium and tin systems, but coupling constant data reflect a diminution of ca. one tenthfold per bond in the order ?[C(1)Sn] > ? [SnC] > ? [CH]. Satisfactory correlations (r > 0.95) are obtained in this series of closely-related compounds among the conventionally recorded two-bond, ²J(SnC¹H) and the constituent, one-bond ¹J (Sn¹³C) and J(¹³C¹H) coupling constants, but the correlation coefficient for the comparison between the two one-bond couplings, ¹J(Sn¹³C) and ¹J(¹³C¹H) is lower (r = 0.872). Changes in the couplings at the methyltin carbon bond tin-119 atoms are interpreted in terms of isovalent hybridization; a model based upon effective nuclear charges is tested with respect to both NMR coupling constants and ¹¹⁹Sn Mössbauer Isomer shifts at tin and is invalidated. Proton and carbon-13 NMR, chemical shift and coupling constant data are used to derive a Hammett σ-constant for the para-trimethyltin group of ?0.14, and the significance of this value is discussed.     

Study of the structural and electronic properties of 1-(4, 5 and 6-selenenyl derivatives-3-formyl-phenyl) pyrrolidinofullerenes

A series of 1-(4, 5 and 6-selenenyl derivatives-3-formyl-phenyl) pyrrolidinofullerenes molecules C₆₀-C₂H₄N-[3-(CHO)C₆H₃SeX] were investigated theoretically by performing Density Functional Theory calculations at the B3LYP/3-21G^∗ level of the theory. The substituents include: X = CN, CH₂CH(NH₂)CO₂H and CH₂CH₂CH(NH₂)CO₂H. We have selected these substituents to be in ortho, meta and para positions with relation to formyl group in order to show the effect of such structural change on the electronic properties of the molecules. The theoretical IR spectra, physical, chemical and thermodynamics properties of the molecules studied are obtained and discussed.     

Design of 2′-phenylethynylpyrene excimer forming DNA/RNA probes for homogeneous SNP detection: The attachment manner matters

1-Phenylethynylpyrene fluorophore (1-PEPy) has long-wavelength shifted emission and higher photostability compared to pyrene, retaining, however, pyrene's ability to form excimers. Here we report the synthesis of 2′-O-[3(and 4)-(pyren-1-ylethynyl)benzyl]-uridines and their tandem incorporation into deoxyribo- and 2′-O-Me-ribo-oligonucleotide probes. Excimer forming probes of type NN … NNXXNN … NN (X = 2′-O-[meta(or para)-(pyren-1-ylethynyl)-benzyl]uridine) containing two adjacent fluorescent nucleosides within an oligonucleotide are available in four types (meta-meta; para-meta; meta-para; para-para). Both DNA (N = deoxyribonucleotides) and 2′-O-Me-RNA (N = 2′-O-Me-ribo-nucleotides) probes were synthesized and their hybridization with complementary and singly mismatched DNA and RNA was studied. Several probes show a dramatic response of their excimer-to-monomer intensity ratio upon hybridization. Remarkably, most spectacular fluorescence changes were demonstrated for probes with para-meta and meta-para combination within 2′-O-Me-ribo-oligonucleotides. Using excimer forming probes, three natural SNP in Helicobacter pylori 23S RNA gene (A2144G, A2143G, A2143C) and the wild type gene can be distinguished.     

ortho-, meta- and para-nitrophenylgold(I) complexes

Treatment of [BzPh₃P][AuCl₂] with [Hg(x-C₆H₄NO₂)₂] (x = o, m, or p) gives anionic gold(I) complexes of the type [BzPh₃P][Au(R)Cl](R = o-, m- or p-C₆H₄NO₂, Bz = C₆H₅CH₂). The chloro ligand in [Au(o-C₆H₄NO₂)Cl]^? can be replaced by bromo or iodo ligands by use of NaBr or NaI. The anions [Au(R)Cl]^? react with neutral monodentate ligands, L, to give neutral mononuclear complexes [Au(R)L] (R = o-C₆H₄NO₂, L = PPh₃, AsPh₃; R = m-C₆H₄NO₂, L = PPh₃) and with 1,2-bis(diphenylphosphino)ethane (dpe) to give [Au₂(R)₂(dpe)] (R = o-C₆H₄NO₂). The corresponding [Au(p-C₆H₄NO₂)Cl]^? reacts with PPh₃ or AsPh₃ to give mixtures containing [AuClL]. The anionic ortho-nitrophenylgold(I) complex is much more stable than its meta- or para-nitrophenyl isomers. These are thought to be the first reports of nitrophenylgold(I) complexes.     

The kinetics of radical polymerization—XXV: Study of the radical reactivity of substituted nitrobenzenes—I

A study was made on the effect of some para- and meta-substituted nitrobenzenes on the radical polymerization of vinyl acetate. It has been shown that −CH₂X and −SO₂X type substituents have merely an inductive effect on the reactivity of nitro groups. It has also been established that the inductive effect of substituents is more intensive when they are in the para position than when in the meta position, i.e.: λ = 1·15.     

Synthesis and structure characterization of unsymmetrical oxacalix[2]benzene[2]pyrazines

The synthesis of two unsymmetrically linked oxacalix[2]benzene[2]pyrazines (1 and 2) is described. X-ray single crystal structure analysis revealed a highly distorted 1,3-alternate conformation of compound 1 (containing ortho- and meta-diphenol components) and a distorted boat conformation of compound 2 (containing meta- and para-diphenol components). Oxacalix[2]benzene[2]pyrazine containing both ortho- and para-diphenol components was not obtained via similar synthetic strategy.     

Mechanism of isomerization of ortho or para bromo phenols in superacids

In superacids ortho or para bromo phenols are isomerized into the meta bromo isomers. In SbF₅-HF, the process is intramolecular and proceeds by a 1,2-Br shift. In CF₃SO₃H, the mechanism involves loss of bromine, followed by meta bromination.     

Quantum Chemical Calculation of Conformations and Rotation Barriers of Functional Groups in Arylsulfonyl Halides

The semiempirical PM3 method is used to calculate the potential functions of internal rotation of the functional groups –SO₂Cl, –NO₂, –CH₃, –OCH₃, and –NH₂ of benzenesulfonyl halide molecules (PhSO₂Hal, Hal = F, Cl, Br, I) and twelve substituted derivatives of benzenesulfonyl chloride. Molecular conformations have been determined and internal rotation barriers of the functional groups have been calculated. For meta- and para-substituted benzenesulfonyl chlorides, the projection of the S–Hal bond is perpendicular to the plane of the benzene ring. The rotation barriers of the –SO₂Hal group of benzenesulfonyl halides increase in the series Hal = F, Cl, Br, I. The rotation barriers of the –SO₂Cl group of benzenesulfonyl chloride with meta- and para-substituents slightly increase with the electron-donor properties of the substituent. The rotation barriers of the functional groups of ortho-substituted benzenesulfonyl chlorides are 3 or 4 times as high as those of the meta- and para-isomers. For para-substituted benzenesulfonyl chlorides, the rotation barriers of the functional groups increase in the order –CH₃, –NO₂, –SO₂Cl, –OCH₃, –NH₂.     

Oxidative bromination of aniline and its derivatives

Oxidative bromination of aniline and its derivatives containing various substituents (CH₃, Cl, NO₂, COOH) in ortho, meta, and para positions with a brominating mixture of NaBr (KBr) and 20–22% hydrogen peroxide in 6–8% hydrochloric acid at the molar ratio aniline : NaBr (KBr) : H₂O₂ : HCl = 1 : 3.5 : 3.2 : 4.5 is described.     

Synthesis of Functionalized o‐, m‐, and p‐Terphenyl Derivatives by Consecutive Cross‐Coupling Reactions of Triazene‐Substituted Arylboronic Esters

Triazene‐substituted arylboronic esters were prepared readily from the corresponding aryl magnesium derivatives and shown to function as a new class of donor–acceptor‐substituted coupling reagents. The selective functionalization of these aromatic derivatives led to a wide variety of terphenyl derivatives in which the original bifunctional unit (often further substituted with another functional group) formed the central aromatic ring. The functionalized terphenyl derivatives were formed in two efficient cross‐coupling steps from the triazene‐substituted boronic esters: Suzuki cross‐coupling with an aryl halide was followed by BF₃?OEt₂‐induced palladium‐catalyzed coupling of the diazonium salt generated in situ from the triazene with an arylboronic acid.     

The reaction of H2PtCl6 with aromatic compounds in CF3COOH/H2O affording theanionic σ-aryl complexes of platinum(IV) : III. The sysnthesis of platinum (IV) complexes of benzenes containing electron-withdrawing substituents

The reaction of H₂PtCl₆ with nitrobenzene, o-nitrotoluene, benzoic acid, acetophenone and diphenyl in a CF₃COOH/H₂O mixture affords the anionic σ-aryl complexes of Pt^IV. In the case of monosubstituted benzenes, mixtures of meta- and para-platinated isomers were prepared. o-Nitrotoluene also gave rise to two isomers. Electron-witdrawing substituents decrease the rate of introducing the platinum moiety into benzene ring.     

A new class of flavonoids bearing macrocyclic polyethers by stereoselective photochemical cycloaddition reaction

A new class of flavonoids bearing cyclic polyethers involving a phenyl ring was conveniently provided by the intramolecular photochemical dimerization of 2-chromonecarboxylic esters. Irradiation of 2-chromonecarboxylate with a polyether tethered at both ends promoted intramolecular [2 + 2] cyclobutane formation leading to 14- to 27-membered cyclic polyethers. The efficiency depended on the substituted position of the phenyl ring, with ortho- and meta-substituted derivatives giving cycloadducts in good chemical yields and quantum efficiencies, whereas the para-derivatives were inert toward photolysis. X-ray crystallographic analysis revealed that the stereochemistry of the macrocyclic cycloadducts exhibited C₂-symmetry.     

Metallation reactions. Part 35: A change of the regiochemistry in the metallation of (alkylthio)arenes

The metallation reaction of bromo(alkylthio)benzenes is described. The results show the complementarity of these reactions with the metal-hydrogen exchange reaction. In fact, monometallation of bromo(methylthio)benzenes afforded products substituted in para or meta or ortho to the thioethereal function while bimetallation led to αS,para, αS,meta and αS,ortho disubstituted products. Analogously, the monometallation of 4-bromo-(isopropylthio)benzene afforded para-monosubstituted and ortho,para-disubstituted products.