Mono-ionizable calix[4]arene-benzocrown-6 ligands in 1,3-alternate conformations: synthesis, structure and silver(I) extraction

Two series of novel mono-ionizable calix[4]arene-benzocrown-6 ligands in 1,3-alternate conformations are synthesized. In one series, the proton-ionizable group (PIG) is attached to the para position of one aromatic ring in the calixarene framework, thereby positioning it over the polyether ring cavity. In the other series, the PIG is a substituent on the benzo group in the polyether ring. This orients the PIG away from the crown ether cavity. In addition to carboxylic acid functions, the PIGs include N-(X)sulfonyl carboxamide groups. With X group variation from methyl to phenyl to 4-nitrophenyl to trifluoromethyl, the acidity of the PIG is ‘tuned’. Solvent extraction of Ag⁺ from aqueous solutions into chloroform is used to probe the influence of structural variation within the mono-ionizable calixcrown ligand on metal ion extraction efficiency, including the identity and acidity of the PIG and its orientation with respect to the polyether ring.     

Electronic effects in dianion radicals of nitro derivatives of 2-phenylbenzimidazole

The EPR spectra of the dianion radicals of 5(6)-nitro-2-(4-aminophenyl)benzimidazole (I), 5(6)-nitro-2-phenylbenzimidazole (II), 5(6)-nitro-2-(4-nitrophenyl)benzimidazole (III), 5(6)-nitro-2-(3-nitrophenyl)benzimidazole (IV), and 2-(4-nitrophenyl) benzimidazole (V), obtained by electrochemical reduction in dimethylformamide (DMF) in a Bu₄NClO₄ -base electrolyte in the presence of Bu₄NOH (VI), were studied. Under the influence of VI, these compounds split out a proton from the imidazole ring and give anions I–V, which are capable of adding an electron reversibly. It was shown that the unpaired electron in I and II is localized in the benzimidazole system and that the splitting of the nitrogen atom of the nitro group does not depend significantly on the substituent in the phenyl ring. The introduction of a nitro group in the phenyl ring (III–V) leads to localization of the unpaired electron on it. The nature of the substituent in the benzimidazole system has a significant effect on the splitting constant for the nitrogen atom of the nitro group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 530–531, April, 1979.We thank T. A. Maslennikova for kindly providing us with the compounds for the investigation.     

Nitration of some 2, 5-disubstituted 4-phenylpyridin es

2,5-Dimethyl-4-phenylpyridine is nitrated in the para position of the phenyl ring. Further nitration of the resulting nitro compound gives a mixture of isomeric dinitro derivatives. In the case of 4-phenylisocinchomeronic acid the nitro group enters the meta position of the phenyl ring.Translated from Khimiya Geterotsiklicheskikh Soedinenii. No. 3, pp. 365–368, March, 1976.     

A New Approach to the Synthesis of 2-Nitrobenzaldehyde. Reactivity and Molecular Structure Studies

 New approaches to the synthesis of 2-nitrobenzaldehyde by formation and selective isomer separation of 2-nitrophenyl-1,3-dioxolane and further hydrolysis are reported. In this route, the same acidic heterogeneous catalyst is used for 1,3-dioxolane formation and hydrolysis; it can be recycled several times without loss of efficiency. The ortho/meta isomers of 2-nitrophenyl-1,3-dioxolane can be separated by a combination of stereoselective crystallization and fractionated distillation. This new route reduces safety and environmental hazards in the synthesis of 2-nitro- and 3-nitro-benzaldehydes. The molecular structures of the nitro derivatives were confirmed by ¹H and ¹³C NMR spectroscopy. The results are in accordance with a non-coplanar conformer of the 2-nitro derivatives (2-nitrobenzaldehyde and 2-(2′-nitrophenyl)-1,3-dioxolane), where the nitro group is twisted with respect to the phenyl ring. In contrary, both the carbonyl and the nitro group are coplanar with the phenyl ring in 3-nitrobenzaldehyde. This result is consistent with the reactivity of the compounds.     

A New Approach to the Synthesis of 2-Nitrobenzaldehyde. Reactivity and Molecular Structure Studies

Summary.  New approaches to the synthesis of 2-nitrobenzaldehyde by formation and selective isomer separation of 2-nitrophenyl-1,3-dioxolane and further hydrolysis are reported. In this route, the same acidic heterogeneous catalyst is used for 1,3-dioxolane formation and hydrolysis; it can be recycled several times without loss of efficiency. The ortho/meta isomers of 2-nitrophenyl-1,3-dioxolane can be separated by a combination of stereoselective crystallization and fractionated distillation. This new route reduces safety and environmental hazards in the synthesis of 2-nitro- and 3-nitro-benzaldehydes. The molecular structures of the nitro derivatives were confirmed by ¹H and ¹³C NMR spectroscopy. The results are in accordance with a non-coplanar conformer of the 2-nitro derivatives (2-nitrobenzaldehyde and 2-(2′-nitrophenyl)-1,3-dioxolane), where the nitro group is twisted with respect to the phenyl ring. In contrary, both the carbonyl and the nitro group are coplanar with the phenyl ring in 3-nitrobenzaldehyde. This result is consistent with the reactivity of the compounds. Received January 22, 2001. Accepted (revised) July 18, 2001     

NMR-Spectroscopic, computational and mass-spectrometric investigations on the cis/trans analogues of 2,3,4-trihydronaphthalene-1-one

NMR-Spectroscopic, computational and mass-spectrometric studies of the cis/trans isomers of N-[8-(acetylamino)-4-(2,2-dimethyl-1,1-diphenyl-silapropoxy)-6-fluoro-5-methyl-1-one-2,3,4-trihydronaphthyl]acetamide (1a and 1b), obtained as intermediates in the synthesis of an important class of alkaloid molecules, are reported. ¹H and ¹³C NMR analyses show an unusual axial preference of the TBDPSi- (tert-butyldiphenylsilyl) group in position 4 in both the isomers. Mass spectrometric evidence demonstrates that trans isomer has a higher affinity for ammonium ions than the cis isomer and that only the ammonium adduct [1b+NH₄]⁺ and the protonated molecule [1b+H]⁺ show the fragmentation in which loss of benzene is observed. Moreover, molecular mechanics and semi-empirical calculations indicate that a group of trans conformers tend to place one of the phenyl rings of the TBDPSiO- group in a offset π-stacked geometry with the compound's aromatic ring. The combination and the detailed analyses of these experimental and theoretical results could support the π-π interaction obtained as a conformational preference in the trans isomer.     

Electron-impact-induced 3,3-sigmatropic rearrangement and cyclization in phenyl allenylmethyl ethers

A 3,3-sigmatropic rearrangement in the M^+· of phenyl allenylmethyl ether is proposed for the observed losses of CO, C₂H₄, and CH₃. Direct cyclization in the M^+· also leads to the [M?CH₃] ion. The presence of sulfur as the heteroatom in phenyl allenylmethyl sulfide does not significantly influence the occurrence of Claisen rearrangement. Ortho interaction of the nitro group with the allenyl double bond in the side chain leads to characteristic fragment ions in 2-nitrophenyl allenylmethyl ether. Linked scans, high-resolution mass spectrometry, collision-activated dissociation-B/E linked-scan spectra, and D-labeling have been employed to support the proposed mechanisms and ion structures.     

Research on imidazo[1,2-a]benzimidazole derivatives

Depending on the nature of the substituent in the 2 position of the heteroring, imidazo[1,2-a] benzimidazole derivatives undergo either mononitration in the 3 position or form dinitro derivatives. In the latter case, one nitro group enters the phenyl group in the 2 position, and the other enters the benzimidazole fragment of the molecule.     

Synthesis of 4-(2-hydroxyaryl)-3-nitro-4H-chromenes

A combinatorial library of 4-(2-hydroxyaryl)-3-nitro-4H-chromenes was synthesized in high yield by C4-SMe substitution in N-alkyl/phenyl 4-(methylthio)-3-nitro-4H-chromen-2-amines with a variety of phenols. The reaction always provided C2 substitution in the phenol ring, dictated by hydrogen bond interactions between the phenolic hydroxyl group and the nitro group in 3-nitro-4H-chromenes. Reduction of the nitro group with concomitant hydrolysis of the enamine in 4-(2-hydroxyaryl)-3-nitro-4H-chromenes with Zn, Ac₂O in AcOH furnished hybrid amino-acid lactone incorporating ortho-tyrosine and phenyl alanine moieties.     

Reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine with phosphorus pentoxide in the presence of nitriles. New method for the generation of aryloxenium ion

A reaction of N-nitro-O-(4-nitrophenyl)hydroxylamine with nitriles RCN (R = Me, Et, Ph) in the presence of P₄O₁₀ in excess amount at 0 °C leads to the formation of 2-R-5-nitro-1,3-benzoxazoles. The reaction presumably takes place through the intermediate (phenoxy)oxodiazonium ion [NO₂C₆H₄O-N=N=O]⁺, which eliminates an N₂O molecule to form the aryloxenium ion [NO₂C₆H₄O]⁺. The latter reacts with nitriles RCN at the ortho-carbon atom of the phenyl ring giving 2-R-5-nitro-1,3-benzoxazoles.     

Novel access to 2-substituted quinolin-4-ones by nickel boride-mediated reductive ring transformation of 5-(2-nitrophenyl)isoxazoles

Reductive ring transformation of 3-substituted 5-(2-nitrophenyl)isoxazoles, readily accessible via 1,3-dipolar cycloaddition of 2-ethinylnitrobenzene with nitrile oxides, opens a novel access to 2-substituted quinolin-4-ones. Nickel boride, generated in situ from nickel chloride and sodium borohydride, allows, via simultaneous reduction of the nitro group and reductive cleavage of the isoxazole ring, the one-step conversion into the target quinolin-4-ones. This protocol tolerates various functional groups, except olefins, and thus is complementary to the reductive ring transformation with iron/acetic acid, which predominantly tolerates olefins.     

Synthesis of 4-(5-Nitrophenylfur-2-yl)-1,2,3-thia- and Selenadiazoles

Arylation of 2-acetylfuran with o-, m-, and p-nitrophenyldiazonium salts under the conditions of the Gomberg-Bachmann reaction has afforded the corresponding 5-(nitrophenyl)-2-acetylfurans. Their carbo-ethoxyhydrazones have undergone the cyclization into stable 4-(5-nitrophenylfur-2-yl)-1,2,3-thiadiazoles under the conditions of the Hurd-Mori reaction. Analogous semicarbazones have afforded the corresponding selenadiazoles upon oxidation with selenium dioxide. The analysis of electronic absorption spectra of the obtained hybrid heterocycles has shown that the conjugation of the phenyl and the furan ring in o-nitrophenyl derivatives is distorted due to steric hindrance, whereas the effect of direct polar conjugation leading to strong bathochromic shift of the absorption band has been observed in the case of the p-nitro derivatives. The position and intensity of the bands in the electronic absorption spectra of the studied compounds are determined by electronic as well as steric factors. The difference in the length of conjugation chain determined by the position of the nitro group in the phenyl fragment also contributes to the observed trend. The introduction of selenadiazole fragment instead of thiadiazole one has caused slight bathochromic shift of the band in the electron absorption spectra.

     

A theoretical study of the structure and vibrations of 2,4,6-trinitrotolune

Theoretical calculations of the structure, internal rotations and vibrations of 2,4,6-trinitrotolune, TNT, in the gas phase were performed at the B3LYP/6-31G* and B3LYP/6-311+G** levels of theory. Two genuine energy minimum structures were found. In both structures the 4-nitro group is planar to the phenyl ring, while the 2,6-nitro groups are slightly out of plane with the phenyl ring due to steric interaction with the methyl group. The two structures are related by internal rotations of the methyl and 2, or 6-nitro group. The lowest energy route for interconversion between them is a concerted motion of the methyl group and 2 or 6 nitro group in a ‘cog wheel’ type of mechanism. The geometry of the low energy structure A is closest to that observed in the crystal structures of TNT, where all three nitro groups are out of plane with the phenyl ring. FTIR and Raman spectra of solid TNT and ¹³C, ¹⁵N enriched TNT are presented and assigned with the help of the B3LYP/6-311+G** calculations on A. The lower level B3LYP/6-31G* calculation fails to predict the correct vibrational coupling between the nitro and phenyl groups. The B3LYP/6-311+G** calculation gives a good prediction of the nitro vibrations and the isotopic shifts observed for TNT isotopomers.     

ZUM MECHANISMUS MASSENSPEKTROMETRISCHER FRAGMENTIERUNGSREAKTIONEN BEI A/B-CIS- VERKNüPFTEN 3α-HYDROXYSTEROIDEN MIT UND OHNE 11-KETOGRUPPE

Mass spectra of steroids containing a carbonyl group in position 11 and a 3α-hydroxy group in a cis connected A/B ring system are characterised by very strong [M – 72]⁺· key ions and may therefore be clearly differentiated from the spectra of their isomers. The mechanism of this fragmentation reaction was investigated by deuterium labelling and the DADI technique. The 3α-hydroxy group is eliminated together with the 9α-H atom. Next a hydrogen atom is transferred from the A ring to the B/C/D ring system. This causes the cleavage of the C-3? C-4 bond and expulsion of C atoms 1 to 4 as butadiene. In 3α-hydroxy-5α-androstanes possessing no 11-keto group an analogous [M – 18]⁺. fragment is fromed, followed by the elimination of ethylene originating mostly from C-1 and C-2.     

Stereochemical studies—XXXVII: Saturated heterocycles—XIII Configuration and conformation of Z- and E-N-methyl- and -N- benzyl-2-p-nitrophenyl-4,5- and -5,6-tetramethylenetetrahydro-1,3-oxazines

The configuration and conformation of Z- and E-N-methyl- and -N-benzyl-2-p-nitrophenyl-4,5-, and -5,6-tetramethylenetetrahydro-1,3-oxazines were determined by ¹H and ¹³C NMR spectroscopy. The Z isomers were proved to be conformationally homogeneous, having the heteroatom in axial and equatorial position, respectively, in the case of the 5,6- and 4,5-tetramethylene compounds. Consequently, the p-nitrophenyl group and the anellated cyclohexyl ring are all-cis arranged in the Z-5,6-tetramethylene compounds while in the case of the Z-4,5-tetramethylene isomers the p-nitrophenyl group and the cyclohexyl ring are trans arranged to the hetero ring.     

Chemical transformations of tetracyclo[3.3.1.1<Superscript>3,7</Superscript>.0<Superscript>1,3</Superscript>]decane (1,3-dehydroadamantane): III. Reactions of 1,3-dehydroadamantane with isothiocyanates

1,3-Dehydroadamantane reacted with phenyl isothiocyanate at 120–130°C under solvent-free conditions to give 4-(adamantan-1-yl)phenyl isothiocyanate. The selectivity of its reactions with benzyl and phenethyl isothiocyanates in which the isothiocyanato group is separated from the benzene ring by methylene or ethylene bridge was lower, and adamantylation of the para position of the benzene ring was accompanied by adamantylation of the methylene groups.     

Cs+ -selective membrane electrodes based on ethylene glycol-functionalized polymeric microspheres

A new strategy for improving the robustness of membrane-based ion-selective electrodes (ISEs) is introduced based on the incorporation of microsphere-immobilized ionophores into plasticized polymer membranes. As a model system, a Cs⁺-selective electrode was developed by doping ethylene glycol-functionalized cross-linked polystyrene microspheres (P-EG) into a plasticized poly(vinyl chloride) (PVC) matrix containing sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl] borate (TFPB) as the ion exchanger. Electrodes were evaluated with respect to Cs⁺ in terms of sensitivity, selectivity, and dynamic response. ISEs containing P-EG and TFPB that were plasticized with 2-nitrophenyl octyl ether (NPOE) yielded a linear range from 10⁻¹ to 10⁻⁵ M Cs⁺, a slope of 55.4 mV/decade, and a lower detection limit (log a_Cs) of −5.3. In addition, these membranes also demonstrated superior selectivity over Li⁺, Na⁺, and alkaline earth metal ion interferents when compared to analogous membranes plasticized with bis(2-ethylhexyl) sebacate (DOS) or membranes containing a lipophilic, mobile ethylene glycol derivative (ethylene glycol monooctadecyl ether (U-EG)) as ionophore.     

Effets de substituants et conformation de stilbenes

Simultaneous study of para nitrostilbenes by X-ray diffraction and ¹³C nuclear magnetic resonance shows a quantitative relationship between the effect of a para nitro substituent on the chemical shift of ethylenic carbon not adjacent to the substituted phenyl ring and the dihedral angle between this phenyl ring and the central double bond. The alternative introduction of substituents in each phenyl ring discloses at the position of carbon β a certain π-polarization which extends to the double bond and to an unsaturated group carried by carbon α.     

Influence de la nature du solvant sur le comportement photochimique de complexes trans- ET cis-[PtCl2(éthylène)(amine)]

Nature of the solvent plays a major role in the photochemical behaviour of cis- and trans-[PtCl₂(ethylene)(amine)] complexes. Dimeric compounds [Pt₂Cl₄-(amine)₂] are obtained on irradiation of these complexes in chloroform or diethyl ether. A non-stereospecific reaction of photosubstitution is observed in nitrile solvents. When methanol, dimethoxyethane or dimethylformamide are used as solvents, cis and trans complexes have a quite different photochemical behaviour, but in all of the cases, a photodegradation leading to ionic species [PtCl₃(ethylene)]^? H⁺ amine and [PtCl₃(amine)]^? H⁺ amine is the main reaction.     

Mass spectrometry of aralkyl compounds with a functional group—VII. On the structure of the ions C8H9+ from C6H5C2H4X- and C9H11+ from C6H5C3H6X-compounds

The C₈H₉⁺-ion, formed from the molecular ions of 2-phenyl-1-bromoethane, 1-phenyl-1-bromoethane and of 1-phenyl-1-nitroethane by loss of the bromine atom and of the nitro group, splits off a molecule of acetylene after an almost complete randomization of hydrogens, as proved by deuteration. An eight-membered ring structure for the C₈H₉⁺-ion is proposed to explain these results. By loss of the nitro group from the molecular ions of 1-phenyl-1-nitropropane and of 1-phenyl-2-nitropropane the well-known phenylated cyclopropane ion3 (C₉H₁₁)⁺ is generated. Mass spectra of analogues, specifically deuterated in the side-chain, show that in this ion a randomization of hydrogen atoms in the cyclopropane ring as well as a hydride transfer from the cyclopropane ring to the phenyl cation occur.