Classes Of Alkanes Research Articles

Proline‐Based P,O Ligand/Iridium Complexes as Highly Selective Catalysts: Asymmetric Hydrogenation of Trisubstituted Alkenes

P,O joins the mix: P,O ligands (L1) form efficient iridium catalysts for the asymmetric hydrogenation of olefins. The proline-derived ligands lead to high enantioselectivities with several classes of alkenes, most notably with α,β-unsaturated carboxylic esters and ketones, where they match or even surpass the ee values reported for the best N,P and C,N ligands. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ChemInform Abstract: Trienamines in Asymmetric Organocatalysis: Diels—Alder and Tandem Reactions.

AbstractA novel activation strategy, named trienamine catalysis, is applied to the Diels—Alder reaction of 2,4‐dienals as trienamine precursors with two classes of olefins.

ChemInform Abstract: Enantioselective Iminium‐Catalyzed Epoxidation of Hindered Trisubstituted Allylic Alcohols.

Abstract The reactivity of diastereomeric biaryl iminium cations made of a ( Ra )-5,5′,6,6′,7,7′,8,8′-octahydrobinaphthyl core and exocyclic appendages derived from ( S )- or ( R )-3,3-dimethylbutyl-2-amine was investigated with hindered trisubstituted allylic alcohols—a class of alkenes which had not been previously studied in detail in epoxidation reactions with cyclic iminium catalysts (ee up to 98%). Surprisingly, generally strong matched/mismatched effects are observed not only in terms of reactivity but also on the enantioselectivity of the reaction (Δee up to 16%). Also, for the most hindered substrates, two sets of reaction conditions were tested in a preliminary study and little advantage was found in running reactions in MeCN/water instead of CH 2 Cl 2 /water/18-C-6. In any case, the presence of the hydroxyl group did not reveal any anchimeric effect.

Enantioselective iminium-catalyzed epoxidation of hindered trisubstituted allylic alcohols

The reactivity of diastereomeric biaryl iminium cations made of a ( Ra)-5,5′,6,6′,7,7′,8,8′-octahydrobinaphthyl core and exocyclic appendages derived from ( S)- or ( R)-3,3-dimethylbutyl-2-amine was investigated with hindered trisubstituted allylic alcohols—a class of alkenes which had not been previously studied in detail in epoxidation reactions with cyclic iminium catalysts (ee up to 98%). Surprisingly, generally strong matched/mismatched effects are observed not only in terms of reactivity but also on the enantioselectivity of the reaction (Δee up to 16%). Also, for the most hindered substrates, two sets of reaction conditions were tested in a preliminary study and little advantage was found in running reactions in MeCN/water instead of CH 2Cl 2/water/18-C-6. In any case, the presence of the hydroxyl group did not reveal any anchimeric effect.

Yields ofβ-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates formed from OH radical-initiated reactions of 2-methyl-1-alkenes

Yields of beta-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates, in particles formed from OH radical-initiated reactions of C(9)-C(15) 2-methyl-1-alkenes in the presence of NO(x) were measured by using a thermal desorption particle beam mass spectrometer coupled to a high-performance liquid chromatograph with a UV-visible (UV-vis) detector. Yields of beta-hydroxynitrates and dihydroxynitrates increased with carbon number primarily due to enhanced gas-to-particle partitioning before reaching plateaus at approximately C(14)-C(15), where the compounds were essentially entirely in the particle phase. Plateau yields of beta-hydroxynitrates, dihydroxynitrates, and trihydroxynitrates were 0.183 +/- 0.005, 0.045 +/- 0.005, and 0.034 +/- 0.005, and, after normalization for OH radical addition to the C = C double bond, were 0.225 +/- 0.007, 0.055 +/- 0.006, and 0.042 +/- 0.006. The fractions of 1-hydroxy and 2-hydroxy beta-hydroxynitrate isomers were 0.90/0.10. Yields measured here and in our previous study of reactions of linear internal alkenes and linear 1-alkenes indicate that, for these alkene classes, the relative branching ratios for forming tertiary, secondary, and primary beta-hydroxyalkyl radicals by OH radical addition to the C=C double bond are 4.3/1.9/1.0, and the branching ratios for forming beta-hydroxynitrates from reactions of tertiary, secondary, and primary beta-hydroxyperoxy radicals with NO are 0.25, 0.15, and 0.12. The effects of H(2)O vapor and NH(3) on yields were also explored.

Phosphoramidite-Controlled Asymmetric Hydrogenation with Rhodium Catalysts

Phosphoramidites, and in particular those derived from BINOL, the MonoPhos family of ligands, have proven extremely useful for the asymmetric hydrogenation of carbon-carbon unsaturation using a rhodium catalyst. Many classes of alkenes can be reduced by these catalyst systems. The use of high-throughput experimentation can be applied to the synthesis of MonoPhos ligands and their subsequent screening, in order to find an appropriate candidate for a specific transformation. Suitable mixtures of ligands can also be found by these high-throughput methods.

Correlations for gas-phase reactions of NO 3, OH and O 3 with alkenes: An update

Methods are developed for predicting rate coefficients for reactions of initiators of tropospheric oxidation with unsaturated compounds that are abundant in the atmosphere; prognostic tools of this kind are essential for atmospheric chemists and modellers. To pursue the aim of exploring such tools, the kinetics of reactions of NO 3, OH and O 3 with a series of alkenes are examined for correlations relating the logarithms of the rate coefficients to the energies of the highest occupied molecular orbitals (HOMOs) of the alkenes. A comparison of the values predicted by the correlations with experimental data (where the latter exist) allowed us to assess the reliability of our method. We used a series of theoretical methods to calculate the HOMO energies, and found that higher computational effort improves the agreement of the predicted rate coefficients with experimental values, especially for reactions of NO 3 with alkenes that possess vinyllic halogen substituents. As a consequence, it is expedient to suggest new correlations to replace those presented by us and others that were based on the lower level of theory. We propose the following correlations for the reactions of NO 3, OH and O 3 with alkenes: ln( k NO 3 /cm 3 molecule −1 s −1)=6.40( E HOMO/eV)+31.69, ln( k OH/cm 3 molecule −1 s −1)=1.21( E HOMO/eV)−12.34 and ln( k O 3 /cm 3 molecule −1 s −1)=3.28( E HOMO/eV)−6.78. These new correlations have been developed using the larger experimental data sets now available, and the impact of the extended data on the quality of the correlations is examined in the paper. Atmospheric lifetimes have been calculated from both experimental and estimated rate coefficients to provide an overview of removal efficiencies for different classes of alkenes with respect to oxidative processes initiated by NO 3, OH and O 3. A figure is presented to show the spatial scales over which alkenes may survive transport in competition with attack by NO 3, OH and O 3. Removal by NO 3 or OH is always more important than removal by O 3, and reactions with NO 3 dominate for scales up to a few hundred metres.

The Intermolecular Pauson—Khand Reaction

AbstractFor Abstract see ChemInform Abstract in Full Text.

The Intermolecular Pauson–Khand Reaction

Five membered carbocycles are important building blocks for many biologically active molecules. Moreover, substituted cyclopentenones (e.g. cyclopentenone prostaglandins) exhibit characteristic biological activity. The efficiency and atom economy of the Pauson-Khand reaction render this process potentially one of the most attractive methods for the synthesis of such compounds. Although it was discovered in its intermolecular form, the scope of the intermolecular Pauson-Khand reaction has always been limited by the poor reactivity and selectivity of the alkene component. The past decade, especially the last three years, has seen concerted efforts to broaden the scope of this reaction. In this overview, we provide a comprehensive and critical coverage of the intermolecular Pauson-Khand reaction based on the reactivity characteristics of different classes of alkenes and a rationalization of successes and misfortunes in this area.

Highly enantioselective epoxidation of styrenes: implication of an electronic effect on the competition between spiro and planar transition states.

Asymmetric epoxidation of various styrenes using carbocyclic oxazolidinone-containing ketone 3 has been investigated. High enantioselectivity (89-93% enantiomeric excess) has been attained for this challenging class of alkenes. Mechanistic studies show that substituents on the ketone catalyst can have electronic influences on secondary orbital interactions, which affects the competition between spiro and planar transition states and, ultimately, enantioselectivity. The results described herein not only reveal the potential of chiral dioxirane catalyzed asymmetric epoxidation as a viable entry into this important class of olefins but also further enhance the understanding of the mechanistic aspects of chiral ketone-catalyzed asymmetric epoxidation.

Reference components of jet fuels: kinetic modeling and experimental results

The goal of this work is to give some kinetic insight on the autoignition and combustion behaviour of full boiling range hydrocarbon fuels. The initial attention is devoted to the selection of possible components of a surrogate that reproduces the reaction behaviour of typical real fuels. n-Dodecane and iso-cetane are the reference components for the different alkane classes, while methylcyclohexane and decalin represented naphthenes and alphamethylnaphthalene represented aromatics. Several oxidation results have been obtained in a pressurized flow reactor both for neat components and selected mixtures. The reactivity maps of the different experiments are reported in terms of CO production. The experimental results clearly confirm that autoignition properties of the mixture cannot be simply reproduced by linear blending rules. Semi-detailed or lumped kinetic models for the oxidation and combustion of pure components are briefly discussed and model predictions are compared with the overall set of experimental measurements. The general agreement with the experimental data, including the mixtures, indicates the viability and interest of the proposed approach.

A General Model for Selectivity in Olefin Cross Metathesis.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A General Model for Selectivity in Olefin Cross Metathesis

In recent years, olefin cross metathesis (CM) has emerged as a powerful and convenient synthetic technique in organic chemistry; however, as a general synthetic method, CM has been limited by the lack of predictability in product selectivity and stereoselectivity. Investigations into olefin cross metathesis with several classes of olefins, including substituted and functionalized styrenes, secondary allylic alcohols, tertiary allylic alcohols, and olefins with alpha-quaternary centers, have led to a general model useful for the prediction of product selectivity and stereoselectivity in cross metathesis. As a general ranking of olefin reactivity in CM, olefins can be categorized by their relative abilities to undergo homodimerization via cross metathesis and the susceptibility of their homodimers toward secondary metathesis reactions. When an olefin of high reactivity is reacted with an olefin of lower reactivity (sterically bulky, electron-deficient, etc.), selective cross metathesis can be achieved using feedstock stoichiometries as low as 1:1. By employing a metathesis catalyst with the appropriate activity, selective cross metathesis reactions can be achieved with a wide variety of electron-rich, electron-deficient, and sterically bulky olefins. Application of this model has allowed for the prediction and development of selective cross metathesis reactions, culminating in unprecedented three-component intermolecular cross metathesis reactions.

Potential for intrinsic and enhanced crude oil biodegradation in Louisiana’s freshwater marshes

This study determined the intrinsic rates of biodegradation of Louisiana “sweet” crude oil (LSCO) in aPanicum hemitomon freshwater marsh using kinetic microcosm studies and verified the results in a large intact core study. In addition, the potential to enhance biodegradation using inorganic nutrient additions was determined. These freshwater marsh soils have high intrinsic rates of degradation (2.0%/day) for the measured alkane fraction (C11–C66) and even higher rates (6.8%/day) for the measured polycyclic aromatic hydrocarbon (PAH) fraction (naphthalene, methylated naphthalenes, phenanthrene, and methylated phenanthrenes). However, there were compound-specific effects with intrinsic rates of degradation highest for the smaller alkanes (C 15) were much lower (0.7–1.2%/day). Results from the intact core study indicate that these rates are similar to those experiencedin situ, with the exception of the PAH fraction, whose rate constants will be substantially lower than those determined in the kinetic study. Nitrogen (ammonium) was primarily the limiting nutrient and increased degradation rate constants (2–3 fold). Few differences were seen between different classes of alkanes after fertilization. Critical nitrogen loading rates (amount needed to produce significant degradation increases) were similar for both the microcosm and core study (2.2–8.8 mg NH4 +-N/g oil), while maximum rates of degradation were observed at higher loading rates (22–44 mg NH4 +-N/g oil). While crude oil degradation can be enhanced by fertilization, the benefits need to be weighed against the presence of high intrinsic biodegradation rates in these systems.

Premating Isolation Is Determined by Larval Rearing Substrates in CactophilicDrosophila mojavensis. III. Epicuticular Hydrocarbon Variation Is Determined by Use of Different Host Plants inDrosophila mojavensis andDrosophila arizonae

Adult epicuticular hydrocarbon profiles of male and femaleDrosophila mojavensis have been implicated as determinants of mate choice leading to premating isolation between geographically isolated populations. Hydrocarbon profiles of a Baja California and a mainland Sonora population ofDrosophila mojavensis, ayellow body mutant strain ofD. mojavensis, and a population ofD. arizonae were compared among flies that had been reared on two cactus substrates and a synthetic laboratory growth medium in order to assess the degree to which natural rearing substrates influence adult hydrocarbon composition. Twenty epicuticular hydrocarbon components, ranging from C29 to C41, were recovered by gas chromatography that represented major classes of alkanes, alkenes, and alkadienes. We found differences in relative amounts of epicuticular hydrocarbons among Baja and mainlandD. mojavensis, and theyellow body mutants. There were few differences betweenD. mojavensis andD. arizonae. The effects of rearing substrates were remarkable: most of the differences were due to the effects of lab food vs. cactus, but there were significant rearing substrate effects due to differences in the two cacti used. Eleven hydrocarbon components differed in abundance between males and females or showed significant sex × rearing substrate interactions from ANOVA. The effects of rearing substrates on epicuticular hydrocarbon composition inD. mojavensis are concordant with changes in the intensity of premating isolation between populations, implicating host ecology as a major determinant in patterns of mate choice in this species.

The common quantum-mechanical problem for the whole class of alkanes as a matrix generalization of the definite two-level problem

Abstract The common hamiltonian matrix for the whole class of alkanes (H) has been considered as a generalization of the definite two-dimensional matrix (h), where the usual Coulomb and resonance parameters are replaced by the N × N-dimensional matrices (N stands for the number of chemical bonds in an alkane). A similar relation between the two analytical expressions for the one-electron density matrices of alkanes and of the relevant two-level two-electron system described by the hamiltonian matrix h has been established. The block-diagonalization procedure for the matrix H following from the Brillouin theorem and resulting in the localized MOs (LMOs) of alkanes has been shown to be an analogous matrix generalization of the usual eigenvalue problem for the two-dimensional matrix h. These results imply a kind of similarity between the class of alkanes and the unique two-level system and form the basis for describing the former as a single quantum-mechanical object. The relation between the actual occupation numbers of the bond orbitals and the extent of delocalization of the respective LMOs and the proportionality of the stabilization energy to the total delocalization of the occupied LMOs have been shown to result from the established similarity between alkanes and the two-level system.

Synthesis of Pyrano[4,3‐b]Azepines by [4 + 2] Cycloaddition of Photochemically Generated 3‐Alkoxycarbonyl‐1,2‐Didehydroazepines with Enol Ethers

Abstract3‐Alkoxycarbonyl‐1,2‐didehydroazepines, generated by photolysis of alkyl 2‐azidobenzoates, undergo a hetero‐[4 + 2] cycloaddition (stepwise or concerted) with ketone‐derived enol ethers to form intensely colored, paratropic 6,8‐dialkoxy‐8,9‐dihydropyrano[4,3‐b]azepines 5–7 which contain the unusual 3‐azaheptafulvene partial structure. Other derivatives of 2‐azidobenzoic acid as well as aldehyde‐derived enol ethers, other classes of olefins, phenol ethers, and furans are unreactive although 2‐methoxynaphthalene undergoes demethylation to produce methyl 2‐(2‐naphthyloxy)‐3H‐azepine‐3‐carboxylate (8). Acid‐catalyzed hydrolysis of the title compounds produces 2‐(acylmethylene)‐2,3‐dihydro‐1H‐azepine‐3‐carboxylates 9 and indoles 10, catalytic hydrogenation generates a tetrahydro derivative 11, and diastereomeric tricarbonyliron complexes 12 are formed with Fe2(CO)9 at the conjugated diene moiety. An intensely colored byproduct 13 of the photolysis reaction is identified as the first known derivative of 3,3′‐diazaheptafulvalene.

Discriminant analysis of leaf wax alkanes in the Lamiaceae and four other plant families

Leaf wax n-alkanes and iso-alkanes were determined in several species of the Lamiaceae and used as chemotaxonomic characters. These alkane classes were also determined in species belonging to Boraginaceae, Verbenaceae, Solanaceae and Scrophulariaceae and the results were compared to those obtained from the Lamiaceae. The plot of area percentages of some n-alkanes and iso-alkanes provided a good partition both inside the Lamiaceae and among the five different families examined. Discriminant analysis provided a much deeper insight into pattern partition confirming the chemotaxonomic usefulness of leaf wax alkanes. The data obtained for Lamiaceae are also discussed with regard to different systematic subdivisions of the family.

A canonical ordering of polybenzenes and polymantanes using a prime number factorization technique

The correlation described over twenty years ago by Matula between the prime factorization of integers and the class of alkanes is re-examined with a view to explaining the probable reason why there have, to date, been no major extensions of this idea. By considering the class of alkanes as a one-dimensional one-parameter system, a new perspective on the method is gained that is amenable to extension, but in a different direction than originally anticipated. With this new perspective, the classes of polybenzenes and polymantanes are seen to be the representatives of two- and three-dimensional one-parameter systems, respectively. A “nomenclature”, comparable to one that Matula used for alkanes, is created that gives a unique canonical name to all possible combinations of either polybenzene or polymantane modules. Such a “nomenclature” contains a “built-in” means of positioning the molecule in the field of interest in accordance with arbitrary pre-selected criteria, such as Patterson's rules, and also coding that indicates symmetries inherent in the structure of this “molecule”.

The second generation regional acid deposition model chemical mechanism for regional air quality modeling

A state‐of‐the‐art gas phase chemical mechanism for modeling atmospheric chemistry on a regional scale is presented. The second generation Regional Acid Deposition Model (RADM2) gas phase chemical mechanism, like its predecessor RADM1, is highly nonlinear, since predicted ozone, sulfate, nitric acid and hydrogen peroxide concentrations are complicated functions of NOx and nonmethane hydrocarbon concentrations. The RADM2 chemical mechanism is an upgrade of RADM1 in that (1) three classes of higher alkanes are used instead of one, (2) a more detailed treatment of aromatic chemistry is used, (3) the two higher alkene classes now represent internal and terminal alkenes, (4) ketones and dicarbonyl species are treated as classes distinct from aldehydes, (5) isoprene is now included as an explicit species, and (6) there is a more detailed treatment of peroxy radical‐peroxy radical reactions. As a result of these improvements the RADM2 mechanism simulates the concentrations of peroxyacetyl nitrate, HNO3, and H2O2 under a wide variety of environmental conditions. Comparisons of RADM2 mechanism with the RADM1 mechanism predictions and selected environmental chamber experimental results indicate that for typical atmospheric conditions, both mechanisms reliably predict O3, sulfate and nitric acid concentrations. The RADM2 mechanism gives lower and presumably more realistic predictions of H2O2 because of its more detailed treatment of peroxy radical‐peroxy radical reactions.