Para Ratio Research Articles

Friedel–Crafts Acylation Reaction using Polymer Supported Aluminium Chloride

Friedel–Crafts reactions using polymer supported AICI3 are reported and the effect of crosslinking level on ortho:para ratio is studied.

Friedel–Crafts Acylation Reaction using Polymer Supported Aluminium Chloride

Friedel–Crafts reactions using polymer supported AlCl3 are reported and the effect of crosslinking level on ortho:para ratio is studied.

A Reinvestigation of Nitration of Phenols with Metal Nitrates under Non-Aqueous and Aprotic Conditions

Nitration of phenol and various 4-substituted phenols with Cu(NO3)2.3H2O, Cu(NO3)2.3H2O/SiO2, 9H2O and Cr(NO3)2. 9H2O in different anhydrous organic solvents are investigated. High selectivity ratio of para vs ortho isomers has been observed. Mono- and dinitro compounds from phenol and 4-substituted phenols by choosing the proper solvents and reaction conditions, are also obtained with high selectivity in excellent yields. Rate enhancement for mononitration of phenols in the presence of LiClO4 with Cu(NO3)2.3H2O is observed.

Hydrogen Dimer Features in the 2-μm Spectra of Saturn and Neptune

We report the detection of the (H2)2dimer in the atmospheres of Saturn and Neptune based on spectra of the fundamentalS1(1) collision-induced band of H2. The lines of this dimer are potentially useful for probing the (H2)2ortho–para ratio and its implications for atmospheric dynamical processes. We also report the detection of the (1–0)S1(1) quadrupole absorption line of monomeric H2in these spectra.

Rearrangement collisions with polarized positron beams and molecular oxygen targets

Angular-momentum coupling and density-matrix techniques are used to study the formation of para- and ortho-positronium in rearrangement collisions involving a slow polarized positron beam and a molecular oxygen target. Spin scattering matrices are obtained by ensuring spin conservation in the interaction region, and spin density matrices for the incoming positron-oxygen system are constructed to include an angular dependence between the spin-quantization axes of the two incoming beams. The ratios of para- to ortho-positronium formation are given for the scattering process O 2 + e + → O 2 + + Ps for an unpolarized as well as a polarized oxygen target. The variation from the statistical value of 1 3 is predicted in both cases. Experimental verification should be possible with modest upgrading of existing positron beam facilities.

The regioselectivity in the fluorination of dibenzofuran, diphenylether and biphenyl with N-F type of reagents

Dibenzofuran, diphenylether and biphenyl were used as a target molecules in an investigation of the effect of N-F type of reagent structure and reaction conditions on the fluorination process. The yields of fluorinated products formed and the regioselectivity depend on the reagent used, and in the reactions with dibenzofuran three products were formed. The ratios of 2-fluorodibenzofuran ( 4) and 3-fluorodibenzofuran ( 5) formed were: 1.3 for 1-fluoro-4-hydroxy-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (NFTh, 1b), 1.4 for 1-chloromethyl-4-fluoro-1,4-diazoniabicyclo[2.2.2]octane bis(tetrafluoroborate) (F-TEDA, 1a), and 1.8 for N-fluoro-2,6-dichloropyridinium tetrafluoroborate (FPD-B, 1c). Ortho regioselectivity predominated for all reagents in the fluorination of biphenyl (ortho : para ratio varied from 4.8 to 1.2), while para attack prevailed for diphenylether (ortho : para = 0.9 – 0.7); however substitution of a phenyl ring by a methyl group enhanced the amount of 2-fluoroanisole. Second order rate constants for the fluorination of aromatic molecules with F-TEDA in acetonitrile at 65°C were established: anisole 4.8×10 −3 Lmol −1s −1, diphenylether 6.0×10 −4 Lmol −1s −1, dibenzofuran 2.5×10 −4 Lmol −1s −1 and biphenyl 1.0×10 −4 Lmol −1s −1.

Anomaly of the Ortho/Para Ratio of Hydrogen Molecules Generated by γ-Irradiation of Solid Alkanes

The gas chromatographic measurement of the ortho (=triplet nuclear spin)/para (=singlet nuclear spin) ratio of hydrogen molecules generated by γ-irradiation of alkanes revealed that the ortho/para ratio depends on the physical phase of alkanes during the irradiation. The ortho/para ratio for liquid alkanes was equal to the high-temperature limit of 3, which implies that the rate of hydrogen atom abstraction from alkanes by hydrogen atoms, the main mechanism of the formation of hydrogen molecules, does not depend on the nuclear spin states of the abstracting and abstracted hydrogen atoms. The ortho/para ratio for solid alkanes was about 2.6, which indicates that hydrogen molecules are trapped for more than a few second adjacent to the alkyl radicals generated in pair with the hydrogen molecules, during which the lattice vibration of the alkyl radicals induces the simultaneous transition of the rotational and the nuclear spin states of the hydrogen molecules. A quantum-mechanical theory of the ortho−para tr...

Adsorption and catalytic properties of MCM-22: The influence of zeolite structure

A combination of infrared spectroscopy and adsorption and microcalorimetric studies of molecules with different kinetic diameters, such as toluene, meta- and orthoxylene, and 1,2,4-trimethylbenzene, together with consecutive adsorption of these molecules, confirms the presence in MCM-22 of 10-membered ring channels and cavities of larger dimensions, both of which can be reached from the external surface. From the kinetic diameters of the adsorbates the dimension of the two types of void species has been estimated. The implications of pore topology on catalysis have been discussed on the basis of selectivity results obtained during alkylation of toluene by methanol and ethanol. The presence of the two types of unconnected cavities determines the ratios of para- to ortho isomers as well as the ratio of mono- to dialkylates.

Detection of absorption by H2 in molecular clouds: A direct measurement of the H2:CO ratio

Vibrational absorption by H2 and CO has been searched for toward infrared sources embedded in molecular clouds. H2 was detected toward NGC 2024 IRS 2 and possibly toward NGC 2264 (GL 989). CO was detected toward both sources. The results are consistent with the H2 ortho:para ratio being equilibrated at the cloud temperature. Toward NGC 2024, H2:CO = (3700(sub -2600)(sup +3100)) (2 sigma limits), and toward NGC 2264, H2:CO less than 6000. Approximately one-third of all carbon is in gas-phase CO.

Isomerization of xylene isomers on a PtRe-H-mordenite catalyst

The isomerization of three xylene isomers was carried out on a catalyst containing 0.35 wt.-% platinum plus 0.35 wt.-% rhenium on hydrogen mordenite in a pulse catalytic microreactor positioned at the inlet of a gas chromatograph. Reactant injections were carried out at temperatures between 300 and 400 °C with hydrogen gas flow at atmospheric pressure. High ratios of para -xylene in the product xylene isomer's mixture relative to the corresponding thermodynamic equilibrium values (2.9–3.5) were obtained, whereas the ratios of meta -xylene (0.33–0.69 ) were low and those of ortho -xylene were very low (0.093–0.18). However, relatively high dealkylation products (toluene and benzene) were obtained at higher temperatures. Disproportionation products (trimethylbenzenes) were not detected in the reaction products.

Observation of nonstatistical ortho–para ratio in hydrogen recombination at low temperatures

We have demonstrated that the molecular hydrogen obtained from atomic recombination at 300 mK has nonstatistic ortho–para ratio. The ortho para conversion is less than 3% in the vibrational relaxation phase. We suggest that it is possible to carry out detailed comparison between calculations and measurements at conditions similar to our experiments.

Reaction of N-aryl- and N-alkyl-benzimidoyl chlorides with silver nitrate

N-Arylbenzimidoyl chlorides, in which the N-aryl group is unsubstituted at the ortho- and para-positions, react with AgNO3 to yield N-(nitroaryl)benzamides in which the NO2 group resides in the ortho- or para-position. N-Arylbenzimidoyl chlorides, in which the N-aryl ring is 2,4,6-trisubstituted, react with AgNO3 to yield the corresponding N-aryl-N-nitrobenzamides. The formation of both types of product can be explained by the intermediacy of an O-nitro imidate. Spectroscopic and chemical evidence is presented for the formation of this intermediate in the reaction of N-(2,4,6-trisubstituted phenyl)benzimidoyl chlorides with AgNO3. Rearrangement of the O-nitro imidate is unimolecular and intramolecular. The rate of rearrangement is independent of the substituent in the C-aryl ring, but increases with the electron-withdrawing ability of the substituents in the N-aryl ring. A mechanism is proposed in which the imidoyl chloride reacts with AgNO3 to produce first a nitrilium ion which goes on to form an O-nitro imidate that subsequently rearranges via a homolytic cleavage of the O–NO2 bond. The ortho:para ratios of N-(nitroaryl)benzamides obtained in the present work indicate that O-nitro imidates are not responsible for the high ½ortho:para ratios sometimes observed in the nitration of anilides.

Chemical processes in dark interstellar clouds – the effects of CNO depletion

The effects of depletion on the elements C, N and O on the chemical composition of dark clouds are investigated, using both isothermal and isochoric cloud models. This work differs from previous approaches in that a much larger range of CNO depletions is considered. The chemistry of the ortho- and para-forms of H 2 and the exothermic reaction between N + and ortho-H 2 , which synthesizes NH 3 , were included. In the isothermal models, the ortho:para ratio is very small at large depletions, but NH 3 formation is still efficient owing to reactions between He + and CN or HCN. In the isochoric models, the equilibrium temperature of the gas is larger, and a thermal ortho:para ratio, which is large enough to drive NH 3 formation, results

Two-phase nitration of phenols, part 3: The nitration of anisole

The two-phase nitration procedure previously described for phenols can be modified to lead to successful nitration of anisole but through a different mechanism. The addition of N(III) species is unnecessary and the reaction is not supressed by nitrous acid traps, the presence of which alters the ortho:para ratio.

Cyclic acetals as carbonyl blocking groups in the photo-fries rearrangement of acyl substituted aryl esters.

The ethylene acetals of o and p -acetoxyacetophenone 3a,b, prepared from the corresponding hydroxyacetophenones by treatment with acetic anhydride in pyridine and subsequently with ethylene glycol and p -toluenesulphonic acid, give upon irradiation the expected photo-Fries products 4a,b (from 3a) or 6 (from 3b). These compounds are converted in part into diacetylphenols 5a,b as a consequence of a deacetalization, occurring to some extent during the irradiation and further in the chromatographic workup. The yields of the photoproducts and the ortho / para ratio (in the case of 3a) are very similar to those given in the literature for phenyl acetate. By contrast, the acetoxyacetophenones 2a,b do not undergo any appreciable change upon irradiation,showing the deactivating effect of the acetyl side chain. Therefore, it is concluded that cyclic acetals are suitable carbonyl blocking groups in order to circumvent the deactivating effect of acyl substituents on the photo-Fries rearrangement of aryl esters.

Aromatic rearrangements in the benzene series. Part 3. Rearrangement of isotopically labelled phenyl benzoates: intermolecularity of the ortho-directed rearrangement. Criteria for determining the intra-/inter-molecularity of aromatic rearrangements

The rearrangement of a mixture of Ph13COOPh and PhCO18OPh (with some unlabelled ester) catalysed by anhydrous AlBr3 in homogeneous solution in chlorobenzene has been examined. Contrary to expectations, more of the 2-hydroxybenzophenone is formed intermolecularly than of the 4-hydroxybenzophenone at the beginning of the reaction, contradicting earlier views that a high ortho : para ratio in such reactions indicates the operation of an intramolecular mechanism. A mechanism is proposed for this stage of the rearrangement involving a cyclic six-membered transition state originating from one molecule of phenyl benzoate and one of Ph–C(OPh)=[graphic omitted]–ĀlBr3, allowing C-acylation by the benzoyl moiety of the catalyst–ester complex to compete with bimolecular ester interchange. This C-acylation can only occur at the ortho-position of the phenoxy-ring of the (uncomplexed) ester molecule, because of steric requirements. This step of the rearrangement is thus necessarily intermolecular. Criteria for judging the intra- or inter-molecularity of aromatic rearrangements are also briefly discussed.

Aromatic rearrangements in the benzene series. Part 4. Intramolecularity of both the ortho- and para-rearrangements of benzyl phenyl ether as shown by labelling experiments

The rearrangement of a mixture of Ph13CH2OPh and PhCH218OPh (with some unlabelled ether) catalysed by AlBr3 in homogeneous solution in 1,2,4-trichlorobenzene and in nitrobenzene has been examined. The literature report of this reaction was shown to be substantially correct: the reaction is very rapid, and ortho-migration of the benzyl group predominates, but does not (in contrast to the earlier report) occur exclusively. The ortho : para ratio of the rearrangement products is ca. 11 in 1,2,4-trichlorobenzene and ca. 4.7 in nitrobenzene. The ether undergoes rearrangement in both solvents without prior scrambling of isotopic labels. In trichlorobenzene, the reaction appears to be almost completely intramolecular, even for para-rearrangement: o-benzylphenol is unscrambled, the para-isomer almost so. In nitrobenzene, o-benzylphenol is virtually unscrambled, the para-isomer ca. 25% so. A mechanism involving a tight ion-pair (from which some leakage occurs in nitrobenzene) is proposed, and possible explanations of the high ortho : para ratios are considered.

Evidence for disequilibrium of ortho and para hydrogen on Jupiter from Voyager IRIS measurements

Specification of the ratio of molecular hydrogen in the ortho state (parallel proton spins) to that in the para state (antiparallel proton spins) has long been a problem encountered in the modelling of the atmospheres of the outer planets1–3. At deeper atmospheric levels where the temperature exceeds 300 K, a ‘normal’ ortho–para ratio of 3:1 will exist; as a parcel is transported upwards to cooler levels, the ratio can either remain fixed or move toward the ‘equilibrium’ value at the local temperature, depending on the relative magnitudes of the equilibration and transport times, neither of which is well known. To make further progress in the investigation of these processes, it is important to determine the ortho–para ratios within the observable portions of the atmospheres of the giant planets. Here we present preliminary results of an analysis of the H2 ortho–para ratio in the atmosphere of Jupiter using Voyager infrared spectrometer (IRIS) data.

Selective Electrosyntheses on Chemically Modified Electrodes: III . Regio‐Selective Anodic Chlorination of Some Benzene Derivatives with a Cyclodextrin Chemically Modified Electrode

The regio‐selective anodic chlorination of some benzene derivatives with an α‐cyclodextrin (α‐CD) chemically modified graphite electrode via “ester bonding” (α‐CD‐CME) and with an α‐CD adsorbed graphite (α‐CD‐AE) was studied. In the C 1s ESCA spectrum of the α‐CD‐CME, a small peak which is considered to be based on carbon atoms in α‐CD appeared at a higher binding energy side of the main peak, indicating that α‐CD can be immobilized on the electrode surface. The immobilized α‐CD as well as the adsorbed α‐CD had a pronounced effect on the para‐position selective chlorination of anisole and toluene, but such an effect could not be observed in the chlorination of chlorobenzene. Increasing the conversion of a substrate resulted in a decrease in the ratio of para‐ to ortho‐chlorination product, ratio, since the products have an inhibition effect on the inclusion of the substrate in α‐CD's cavity. Although the homogeneous chlorination by in the presence of α‐CD in solution also showed a relatively high p/o ratio, it revealed that the ratio observed in the electrochemical method was slightly higher than that observed in the homogeneous method. The α‐CD‐CME used repeatedly showed relatively high regio‐selectivity even after a month of immersion of the electrode in water, whereas the α‐CD‐AE showed decrease of the p/o ratio with increasing immersion time.

ChemInform Abstract: 2‐HYDROXYACETOPHENONE VIA FRIES REARRANGEMENT AND RELATED REACTIONS. A COMPARATIVE APPLIED STUDY

AbstractDie Herstellung von Phenylacetat (II) durch Umsetzung von Phenol (I) mit Essigsäure in Gegenwart von Protonensäuren oder sauren Ionenaustauschern wird untersucht.