The influence of the macroring structure on the enthalpies of solution of tetrapyridylporphyrin derivatives in water

The enthalpies of solution of 5,10,15,20-tetra(N-methylpyrid-4,3,2-yl)porphyrin tetraiodide were determined calorimetrically at 298.15 K. Changes in the position of the heteroatom in the pyridyl fragment of the substituted porphyrin (meta- and ortho- positions) substantially decreased the endothermic effect of solution compared with the para- isomer. This was related to changes in the energy of the molecular crystal lattice, which decreased in the series para- > meta- > ortho-isomer.     

Heterocycles Based on Sterically Hindered Phenols and their Derivatives. (Review)

Published data on the synthesis of heterocyclic compounds (derivatives of dibenzofuran, phenoxazine, benzodioxolane, etc.) based on sterically hindered 6-substituted 2,4-di-tert-butylphenols, 6-hydroxy-2,4- and 6-hydroxy-2,5-di-tert-butylphenols, and their redox-conjugated ortho-benzoquinones are reviewed.     

Advanced adsorbents for the separation of the ortho- and para-hydrogen spin isomers at cryogenic temperatures

Improved adsorbent types and compositions have been developed for the challenging separation of the ortho- and para-hydrogen spin isomers at 77 K. From a systematic study of commercially available adsorbent types, it has been found that zeolites of type X offer the largest capacity and selectivity towards ortho-hydrogen and that performance is significantly impacted by the cation type and the number of cations present in the zeolite. For the present separation improved performance was obtained with larger Group I cations, especially K and Cs. Another key property of the adsorbents addressed in the present work is the need to control the adsorbent composition to avoid unwanted catalytic conversion of the para- to ortho-hydrogen. A common source of unwanted catalytic activity in many adsorbent compositions was identified as the presence of unwanted transition metal impurities, especially iron associated with the natural clays, commonly employed as binding agents in the commercial agglomerated zeolite products. To avoid this, equivalent adsorbent compositions were agglomerated instead using colloidal silica binding agents which successfully minimize back conversion of the para- to ortho-hydrogen and produced adsorbents with higher capacities and selectivities for the ortho component at the test temperature of 77 K. These advanced adsorbents can be applied in more efficient hydrogen liquefaction processes.     

A new biologically active molecular scaffold: crystal structure of 7‐(3‐hydroxyphenyl)‐4‐methyl‐2H‐[1,2,4]triazolo[3,2‐c][1,2,4]triazole and selective antiproliferative activity of three isomeric triazolo–triazoles

A study of three isomeric compounds containing a phenolic moiety attached to the nitrogen‐rich triazolo–triazole bicycle is presented. In the three isomers, the phenolic OH group is in the ortho, meta and para positions. The crystal structure analysis of the meta isomer (C₁₀H₉N₅O) shows that the 2H‐tautomer is present in the crystal and that the molecule adopts a substantially planar geometry. However, the conformation found in the crystal is different compared to the monoprotonated cation of the same compound previously investigated in several salts. The packing of the meta isomer is driven by the formation of strong hydrogen bonds and shows the formation of infinite planar ribbons, parallel to a, formed around 2₁ crystallographic axes. The three isomers were tested against some cancer cell lines and also against normal cell lines. The ortho isomer shows a weak antiproliferative activity, the meta isomer shows significant antiproliferative activity against some cancer lines and no activity against healthy cell lines, and the para isomer is active against all the tested cell lines.     

Metal cation extraction properties of linear all-ortho phenolic oligomers

A series of ethyl acetate (nBP-Es) and trioxyethylene ether (nBP-OE) derivatives of linear all-ortho methylene-linked oligomers of p-tert-butylphenol (n = 1–7) were prepared, and cation extraction properties were determined. For alkali metal cations, nBP-Es showed the affinity, and especially 5BP-Es showed the selectivity for Na⁺. On the other hand, nBP-OE also showed sufficient affinity; however, the extraction behavior was completely different from that of nBP-Es, that is, the affinity of even membered BP-OE was higher than that of the odd membered. nBP-Es extracted cations by forming a cavity winding around them, while nBP-OE extracted with two trioxyethylene chain picking up cations. For alkaline earth metal cations, nBP-Es extracted more than that for alkali cations. Particularly, 7BP-Es showed the highest affinity for larger cations, Sr²⁺ and Ba²⁺, among phenolic oligomers and 18-crown-6 compound. On the other hand, nBP-OE showed a lower affinity than that for alkali cations. It was concluded that the linear phenolic oligomers extracted alkali and alkaline earth metal cations and the kind of ion ligand introduced influenced the affinity and the selectivity. © 1996 John Wiley & Sons, Inc.     

Oxidation of 2-dialkylaminomethyl-4,6-di-tert-butylphenols

Oxidative transformations of 2-dialkylaminomethyl-4,6-di-tert-butylphenols depend on the nature of the oxidant, the character of the substituents at the nitrogen atom, and the medium. A mechanism of the oxidation of these compounds is suggested. The molecular structure of the compound obtained as a result of oxidative trimerization of 2-dimethylaminomethyl-4,6-di-tert-butylphenol was established by X-ray structural analysis. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1328–1335, July, 1997.     

Competitive solvent extraction of alkaline earth metals by ionizable nano-baskets of calixarene

The competitive solvent extraction of alkaline earth metals using different nano-baskets was investigated. The novelty of this work is to study the correlations between the isomer structure of calixarenes and their extraction properties. The objective was to quantify the effects of aryl groups in the ionisable pendant moieties, calixarene conformation, steric orientations (cis- and trans-) and relative positions (ortho- and para-) of pendant moieties upon the extraction efficiency, pH_1/2 and the selectivity of calix[4]arene complexes. Alkaline earth metals were extracted from aqueous solutions into chloroform by di-ionisable calix[4]arenes and were measured using ion chromatography. The results revealed that alternation of aryl group in the pendant moieties, changing their orientation from cis- to trans-analogues as well as from ortho- to para- analogues, showed no changes in the selectivity, the extraction efficiency and the pH_1/2 of calix[4]arene complexes. Changing the scaffold of calixarene's ring to the cone, 1,2-alternate and partial-cone conformers altered their complexation ability towards alkaline earth metals and their extraction efficiency.     

Infrared spectra ofortho-substituted acetanilides: Vicinal effects and conformation

Summary The infrared spectra of twenty-twoortho-substituted acetanilides (1a–1v) in CCl₄ and CHCl₃ were measured in the region of the C=O and NH stretching vibrations and compared with those ofpara-substituted acetanilides (2a–2i). The wave numbers of the C=O stretching vibrations were analyzed using empirical substituent constants and single- and multiparametric correlations. On the basis of the above approaches, the separation of the polar effects into inductive, field, resonance, and steric components has been assessed for theortho-substituted series. For compounds containing polar substituents with double bonds, specific vicinal effects caused by intramolecular hydrogen bonding have been observed. The conformations ofortho-substituted acetanilides1a–1v were studied by both infrared spectroscopy and AM1 calculations.

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Infrarotspektren vonortho-substituierten Acetaniliden: Nachbargruppeneffekte und Konformation

Zusammenfassung Die Infrarotspektren von 22ortho-substituierten Acetaniliden (1a–1v) in CCl₄ und CHCl₃ wurden im Bereich der C=O- und NH-Streckschwingungen gemessen und mit jenen vonpara-substituierten Acetaniliden (2a–2i) verglichen. Die Wellenzahlen der C=O-Streckschwingungen wurden mit Hilfe empirischer Substituentenkonstanten und ein- und mehrparametriger Korrelationen untersucht. Auf dieser Grundlage konnte für dieortho-substituierte Reihe eine Zerlegung der polaren Effekte in induktive, feldbedingte, resonanzabhängige und sterische Komponenten erzielt werden. In Verbindungen mit Doppelbindungen enthaltenden polaren Substituenten wurden durch intramolekulare Wasserstoffbrückenbindungen hervorgerufene spezifische Nachbargruppeneffekte beobachtet. Die Konformationen derortho-substituierten Acetanilide1a–1v wurden sowohl infrarotspektroskopisch als auch mittels AM1-Rechnungen untersucht.

     

Reversal of order of chemical shifts. Differential solvent effects in the hydrogen shifts of toluene,m-xylene and o-xylene as determined by 320 MHz tritium NMR spectroscopy

Chemical shifts for the aromatic tritons of toluene decrease in the order meta>para>ortho for pure toluene, but in the order meta>ortho>para for dilute solutions of toluene in carbon tetrachloride, chloroform, cyclohexane and dimethyl sulphoxide; m-xylene shifts are 5>4,6>2 in the pure state and 5>2>4,6 in carbon tetrachloride and dimethyl sulphoxide; o-xylene shifts are 4,5>3,6 in the pure state and reversed in carbon tetrachloride.     

QSPR study on pK<Subscript>a</Subscript> values of N-methoxy-polynitroaniline derivatives

A QSPR study is presented for acidities of thirteen N-methoxy-polynitroaniline derivatives. Hammett σ values are known for meta and para substituents, and in the present study values are introduced for ortho-substituents in these N-methoxy-polynitroaniline derivatives. Hammett σ values for ortho-substituents in these N-methoxy-polynitroaniline derivatives were obtained by multiplying para values with 0.65.     

Analytical MO study of the singlet–triplet coupling in xylylenes

The singlet–triplet energy difference in para-, meta-, and ortho-xylylenes is studied as the interaction of two radical centers through the benzene ring. An SCF perturbative procedure adapted to open-shell systems leads to two benzyl-like nonbonding molecular orbitals (NBMOS ) and to benzene-like occupied and vacant MOS whatever the xylylene isomer. The superposition of these NBMOS in para-, meta-, and ortho-positions and their interaction with the benzene-like MOS lead, at the configuration interaction level, to the following results: The exchange energy (which favors the triplet state) and the charge transfer energy (which favors the singlet state) are important only in the meta-xylylene; the dynamic (or double) spin polarization favors the triplet in meta and the singlet in para and ortho-isomers; the super-exchange energy (which favors the singlet) is important only in para- and ortho-isomers. The above results are independent of the chosen geometry.     

Selective initiation of nonconjugated dienes containing electron donor–electron acceptor systems. II. Polymerization studies of vinyl ether–β-nitrostyrenes

The monomer series, o-, m-, and p-(2-vinyloxyethoxy)-β-nitrostyrenes, was studied. All three monomers were selectively polymerized through the electron-donating vinyloxy group via cationic initiation. The linear polymers from the meta and para isomers containing the electron-accepting nitrovinyl group were readily crosslinked via anionic initiation. The polymer derived from the ortho isomer was not crosslinked by this mechanism, an observation in accord with results previously reported from these laboratories in which it was shown that all o-substituted-β-nitrostyrenes having ortho substituents larger than fluorine exhibited a sterically inhibited propagation step. The meta and para isomers of this series were selectively polymerized through the electron-accepting nitrovinyl group via anionic initiation. Because of the fact that the resulting polymers were soluble only in highly polar solvents, subsequent crosslinking of these polymers via cationic initiation could not be accomplished. However, these polymers showed strong tendencies to undergo crosslinking upon long exposure to air. Because of the sterically induced ortho effect referred to above, no significant polymerization occurred in the case of the ortho isomer of this series via anionic initiation. However, it was shown in this case that initiation via the anion was rapid, and that the slow step was propagation.     

Effects of acyl donor type, catalyst type, and reaction conditions on the activity and selectivity of Friedel-Crafts acylation

Acylation of anisole and 3-methylanisole was performed with several acylating reagents (acetylation by AcCl and Ac₂O and bromoacetylation by BrAcCl and (BrAc)₂O) over different solid acid catalysts. The reaction conditions were optimized with respect to the acylation reagent, overall yield, solid acid catalyst, and the products selectivities. While acylation of anisole with acetyl chloride or acetic anhydride resulted in its full conversion to para-substituted acetophenone, the use of bromoacetyl bromide or bromoacetic anhydride yielded also the ortho-substituted product. Acylation of 3-methylanisole also yielded both para- and ortho-substitutions, and the products distribution was affected by the reaction conditions and catalyst type. It was found that while more acidic catalysts (caesium salt of heteropolyacid and zeolites) were the most active towards anisole acylation, the most active catalysts for the acylation of 3-methylanisole were ion-exchange catalysts. Employing HY-740 zeolite resulted in the highest ortho-selectivity in the acylation of anisole with bromoacetyl bromide and bromoacetic anhydride and in the acylation of 3-methylanisole with acetic anhydride.     

Separating Para and Ortho Water

Water exists as two nuclear‐spin isomers, para and ortho, determined by the overall spin of its two hydrogen nuclei. For isolated water molecules, the conversion between these isomers is forbidden and they act as different molecular species. Yet, these species are not readily separated, and no pure para sample has been produced. Accordingly, little is known about their specific physical and chemical properties, conversion mechanisms, or interactions. The production of isolated samples of both spin isomers is demonstrated in pure beams of para and ortho water in their respective absolute ground state. These single‐quantum‐state samples are ideal targets for unraveling spin‐conversion mechanisms, for precision spectroscopy and fundamental symmetry‐breaking studies, and for spin‐enhanced applications, for example laboratory astrophysics and astrochemistry or hypersensitized NMR experiments.     

Tetraphenylporphyrins monosubstituted with glycerol derivative units in the phenyl rings. Synthesis and characterization

Summary The synthesis and spectroscopic characterization of a series ofmeso-tetraphenyl substituted porphyrins appended with glycerol, diacetylglycerol, or isopropylideneglycerol units inortho,meta, orpara position of the phenylene ring is described.

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Synthese und Charakterisierung von an den Phenylresten mit Glycerinderivaten monosubstituierten Tetraphenylporphyrinen

Zusammenfassung Synthese und spektroskopische Charakterisierung einer Reihe von an den Phenylringen inortho-,meta- oderpara-Position mit Glycerin, Diacetylglycerin oder Isopropylidenglycerin substituiertenmeso-tetraphenylsubstituierten Porphyrinen wird beschrieben.

     

Hydroxynitrobenzodifuroxan and its salts

The synthesis and properties of hydroxynitrobenzodifuroxan (5‐nitro[1,2,5]oxadiazolo[3,4‐e][2,1,3]ben‐zoxadiazol‐4‐ol‐3,8‐dioxide) ( 1 ) and its salts (four metal and three amine salts) are described. Crystal structure analyses indicate that the hydroxynitrobenzodifuroxan materials can exist in two forms. One form is the isomer in which the oxy and nitro group are in positions ortho to each other. In the other form, these groups are para to each other.     

Organometallic derivatives of 2,6-di-tert-butylphenols as specific inhibitors of methyl oleate oxidation

2,6-Di-tert-butylphenols containing the Pt—SnCl₃ and Pt—GeCl₃ groups in the para position exert a dual effect on the oxidation of methyl oleate by molecular oxygen. Initially, these compounds act as antioxidants producing the corresponding phenoxyl radicals whose decomposition is accompanied by elimination of SnCl₂ and GeCl₂, which are oxidation promoters.     

Hydrogenation of 2- tert -butylphenol over Ni catalyst

The hydrogenation of 2-tert-butylphenol was studied in regard to possibilities of influencing selectivity, namely the ratio ofcis- andtrans-isomers of 2-tert-butylcyclohexanol in the final reaction mixture. The hydrogenation reactions were carried out using the catalyst Ni/Al₂O₃. During the hydrogenations, a higher content of thecis-isomer was attained, when simultaneously the final reaction mixture contained 2-tert-butylcyclohexanone. The content of this intermediate, which primarily hydrogenated to thecis-isomer, increased with a decreased pressure and after the addition of acetic acid into the reaction mixture.     

Band‐Gap Manipulations of Monolayer Graphene by Phenyl Radical Adsorptions: A Density Functional Theory Study

Phenyl radical (Ph^.) adsorption on monolayer graphene sheets is used to investigate the band‐gap manipulation of graphene through density functional theory. Adsorption of a single Ph^. on graphene breaks the aromatic π‐bond and generates an unpaired electron, which is delocalized to the ortho or para position. Adsorption of a second radical at the ortho or para position saturates the radical by electron pairing and results in semiconducting graphene. Adsorption of a second radical at the ortho position (ortho–ortho pairing) is found to be more favorable than adsorption at the para position (ortho–para pairing), and the ortho–ortho pairing has stronger effects on band‐gap opening compared with ortho–para pairing. Adsorption of even numbers of Ph^. on graphene by ortho–ortho and ortho–para pairings, in general, increases the band gap. Our study shows promise of band‐gap manipulation in monolayer graphene by Ph^. adsorption, leading to potential wider applications of graphene.     

Synthesis of Tetrahydrobenzazepinesulfonamides and Their Rearrangement to Diarylsulfones

A new class of diarylsulfones, in which tetrahydrobenzazepine comprises one of the aromatic moieties, has been synthesized via the acid‐catalyzed rearrangement of several substituted benzazepinesulfonamides. The rearrangement is normally ortho but in at least one case a para isomer is also formed. Sulfones of this type have been shown to possess potent anti‐HIV activity.