Separation of fuels,heavy fractions,and crude oils into compound classes: A review

Practically all the conventional chromatographic techniques are used in the characterization of the highly complex mixtures of organic compounds occurring in fuels, heavy fractions, and crude oils. This paper surveys the techniques employed for class determination, preparative fractionation of the main classes, and determination of subgroups after class fractionation.     

Coordinating ability of the heterocycles 1,3-dithia-2-arsa and stiba-cyclopentanes toward sulfur containing ligands,part I. Dialkyl-dithiocarbamate complexes

Summary The heterocyclic compounds ClMS₂ (CH₂)₂ (M = As, Sb) are tested by first time as source of starting materials in the synthesis of complexes. The preparation and characterization of heterocyclic dithiocarbamatesR ₂NCS₂ MS₂ (CH₂)₂, (M = As, Sb;R =Me,Et,i-Pr) is reported. Spectroscopic and analytical data suggest a bidentate behavior of the dithiocarbamate entity and the presence of aMS₄ core.

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Die Koordinationsfähigkeit der Heterocyclen 1,3-Dithia-2-arsa- und-stiba-cyclopentan gegenüber Schwefel enthaltenden Liganden, I. Dialkyldithiocarbamat-Komplexe

Zusammenfassung Die heterocyclischen Verbindungen ClMS₂ (CH₂)₂ (M = As, Sb) werden erstmals als Quelle für Ausgangsmaterial zur Synthese von Komplexen herangezogen. Es wird über die Herstellung und Charakterisierung der heterocyclischen DithiocarbamateR ₂NCS₂ MS₂ (CH₂)₂ (M = As, Sb;R =Me,Et,i-Pr) berichtet. Spektroskopische und analytische Daten sprechen für ein bidentates Verhalten der Dithiocarbamat-Einheit und der Präsenz einerMS₄-Anordnung im Komplex.

     

Cobalt-mediated approach for the synthesis of terpene-based hybrids

[structure: see text] Dicobalt-beta-pinene hybrids of types I and II have been prepared using a Nicholas reaction between propargyl derivatives, obtained from commercial (1R)-(-)-myrtenal, and different aromatic nucleophiles. The method is suitable for the preparation of densely functionalized bio-organometallic natural product-based hybrids, as demonstrated by the preparation of a beta-pinene-neoclerodane hybrid.     

Precise and accurate quantitative C NMR with reduced experimental time

In order to detect small variations in ¹³C isotopomers concentrations, high sensitivity, accuracy and precision have to be achieved. To assess such criteria, when using ¹³C NMR, ¹³C bi-labelled ethanol has been proposed as a molecular probe. Advantage has been taken of the pre-established structural relationship between the peak areas of the ¹³C NMR spectrum of this molecule, i.e. the ratio of signal areas is set to a fixed value. It is shown that the quality performance, required by quantitative ¹³C NMR spectroscopy, is not affected by a large reduction of the repetition delay using relaxation reagents.     

Spectroscopic probing of the effect of alkanols on the properties of the head group region in reverse micelles of AOT-heptane-water

The effects of addition of alkanols (ethanol, n-hexanol, and 3-ethyl-3-pentanol) on the micropolarity and microviscosity of the head group region in reverse micelles of AOT-heptane-water have been investigated by fluorescence probing methods (ANS fluorescence yield and TMADPH fluorescence anisotropy), complemented by the use of the solvatochromic probe E(T)(30) in absorption spectroscopy. For all the alkanols considered, ANS fluorescence in AOT reverse micelles (at W=3) is quenched by additive incorporation, being the effect elicited almost independent of the alkanol chain length and topology. As sensed by the E(T)(30) parameter, the micropolarity of the micelle surface increases, remains unmodified, and decreases upon addition of ethanol, 3-ethyl-3-pentanol, and hexanol, respectively. While ethanol barely modifies the fluorescence anisotropy of TMADPH, 3-ethyl-3-pentanol and n-hexanol addition strongly decrease it. The similarity of the tendencies of ANS data to TMADPH anisotropies and the differences between ANS data and E(T)(30) values would indicate that, at least for 3-ethyl-3-pentanol and n-hexanol, microviscosity, rather than micropolarity, must be considered to interpret the effect of the alkanols upon the fluorescent behavior of ANS.     

Heavy-Atom Tunneling in Semibullvalenes: How Driving Force,Substituents, and Environment Influence the Tunneling Rates

The Cope rearrangement of selectively deuterated isotopomers of 1,5-dimethylsemibullvalene 2 a and 3,7-dicyano-1,5-dimethylsemibullvalene 2 b were studied in cryogenic matrices. In both semibullvalenes the Cope rearrangement is governed by heavy-atom tunneling. The driving force for the rearrangements is the small difference in the zero-point vibrational energies of the isotopomers. To evaluate the effect of the driving force on the tunneling probability in 2 a and 2 b , two different pairs of isotopomers were studied for each of the semibullvalenes. The reaction rates for the rearrangement of 2 b in cryogenic matrices were found to be smaller than the ones of 2 a under similar conditions, whereas differences in the driving force do not influence the rates. Small curvature tunneling (SCT) calculations suggest that the reduced tunneling rate of 2 b compared to that of 2 a results from a change in the shape of the potential energy barrier. The tunneling probability of the semibullvalenes strongly depends on the matrix environment; however, for 2 a in a qualitatively different way than for 2 b .     

The Benzylperoxyl Radical as a Source of Hydroxyl and Phenyl Radicals

The benzyl radical ( 1 ) is a key intermediate in the combustion and tropospheric oxidation of toluene. Because of its relevance, the reaction of 1 with molecular oxygen was investigated by matrix‐isolation IR and EPR spectroscopy as well as computational methods. The primary reaction product of 1 and O₂ is the benzylperoxyl radical ( 2 ), which exists in several conformers that can easily interconvert even at cryogenic temperatures. Photolysis of radical 2 at 365 nm results in a formal [1,3]‐H migration and subsequent cleavage of the O?O bond to produce a hydrogen‐bonded complex between the hydroxyl radical and benzaldehyde ( 4 ). Prolonged photolysis produces the benzoyl radical ( 5 ) and water, which finally yield the phenyl radical ( 7 ), CO, and H₂O. Thus, via a sequence of exothermic reactions 1 is transformed into radicals of even higher reactivity, such as OH and 7 . Our results have implications for the development of models for the highly complicated process of combustion of aromatic compounds.     

Inherently Chiral Macrocyclic Oligothiophenes: Easily Accessible Electrosensitive Cavities with Outstanding Enantioselection Performances

Linear conjugated oligothiophenes of variable length and different substitution pattern are ubiquitous in technologically advanced optoelectronic devices, though limitations in application derive from insolubility, scarce processability and chain‐end effects. This study describes an easy access to chiral cyclic oligothiophenes constituted by 12 and 18 fully conjugated thiophene units. Chemical oxidation of an “inherently chiral” sexithiophene monomer, synthesized in two steps from commercially available materials, induces the formation of an elliptical dimer and a triangular trimer endowed with electrosensitive cavities of different tunable sizes. Combination of chirality with electroactivity makes these molecules unique in the current oligothiophenes literature. These macrocycles, which are stable and soluble in most organic solvents, show outstanding chiroptical properties, high circularly polarized luminescence effects and an exceptional enantiorecognition ability.