Showing papers on "Double bond published in 1996"
TL;DR: In this paper, the 13C NMR lines at 60, 70, and 130 ppm were assigned to C−OH, C−O−C, and >CC CC< double bonds.
Abstract: Graphite oxide (GO) and its derivatives have been studied using 13C and 1H NMR. The 13C NMR lines at 60, 70, and 130 ppm are assigned to C−OH, C−O−C, and >CC CC< double bonds are relatively stable, while C−OH groups may condense to form C−O−C (ether) linkages. There are at least two magnetically inequivalent C−OH sites, and the structure does not necessarily possess long-range order. Water molecules interact very strongly with the structure. The results reveal a number of new structural features.
408 citations
Patent•
20 Mar 1996TL;DR: In this article, a polysiloxane with an alpha, omega-diene was used to make a silicone gel, which can then be crumbled into a silicone powder using mechanical force.
Abstract: Silicone gels are made by reacting an .tbd.Si--H containing polysiloxane with an alpha, omega-diene. The reaction is conducted in the presence of a platinum catalyst and in the presence of a low molecular weight silicone oil. The reaction is continued until a gel is formed by crosslinking and addition of .tbd.Si--H across double bonds in the alpha, omega-diene. The silicone gel can then be crumbled into a silicone powder using mechanical force. When additional amounts of low molecular weight silicone oil are added to the gel, and the silicone oil and the gel are subjected to shear force, a silicone paste can be formed.
311 citations
TL;DR: The double bond rule has long since been surpassed due to improved experimental and quantum chemical methods which have allowed the synthesis of main group analogues of methylene, ethylene, and cyclopropane that are kinetically stable in solution and the solid state at room temperature as discussed by the authors.
Abstract: For a long time methylene (:CH2), ethylene (H2CCH2), and cyclopropane [(CH2)3] were considered as compounds whose higher main group homologues or analogues could not be synthesized. One consequence of the failure of earlier experiments was, for example, the “double bond rule” which was introduced over twenty years ago and is still often quoted. Although it does not dispute the existence of multiple bonding between elements, it states that it leads to very kinetically unstable species. This interpretation of the double bond rule has long since been surpassed due to improved experimental and quantum chemical methods which have allowed the synthesis of main group analogues of methylene, ethylene, and cyclopropane that are kinetically stable in solution and the solid state at room temperature. In the following review recent advances in the synthesis of these compounds will be referenced, and the concepts, which were developed by a systematic study, will be laid out. In doing so, a detailed description of the complex reactivity of the individual classes of compounds will be avoided in order to highlight the basic principles. These can then be used to approximately predict reactivity and characteristics of new compounds. There are significant differences between formally and even structurally analogous compounds with elements from the higher rows as compared to their “lighter” homologues. For example, while every chemist is familiar with the planar D2h symmetrical structure of H2CCH2 as the only “significant” isomer, it must be accepted that Sn2H4 has four isomers that are separated by very small energy differences. For cis/trans isomerism of olefins only the rotation of the CC double bond needs to be considered, but there are three possible mechanisms for the disilene derivatives R1RSiSiR1R. In the last century cyclopropane was considered to be not producible and this provided the impetus for Baeyer's strain theory. Investigations into small silicon cycles, which were discovered much later, show that this theory has more validity for these rings. As a result of the collected data, it is slowly becoming clearer that precisely the carbon compounds once seen as mere models are in reality the “exotic” compounds. Rules with broader applications can be developed by studying the compounds made up of main group elements.
249 citations
TL;DR: Low-energy negative-ion electrospray mass spectrometry (ESI-MS) and ESI-MS/MS were used to characterize saturated and unsaturated fatty acids and the utility of this technique to examine biological samples was shown by analysis of the fatty acid composition of cod liver oil.
Abstract: Low-energy negative-ion electrospray mass spectrometry (ESI-MS) and ESI-MS/MS were used to characterize saturated and unsaturated fatty acids. The carbon number and degree of unsaturation of fatty acids were determined using ESI-MS, and MS/MS was used to localize some double bond positions of mono-and polyunsaturated fatty acids. For compounds with up to two unsaturated bonds, fragmentation was dominated by loss of H2O from the carboxyl moiety and very low-intensity peaks generated from bonds cleaved at carbons alpha and/or beta to sites of unsaturation. Fragmentation of monounsaturated fatty acids was minimal using this soft method of mass spectrometric analysis, but increased with progressively greater degrees of fatty acid unsaturation. There was extensive hydride migration during ESI-MS/MS of compounds with three or more double bonds. Although this behavior complicated localization of double and triple bonds, the spectra were reproducible. Many peaks could not be definitively assigned to specific product ions, but the spectra of standards and complementary natural products were similar and isobaric compounds could be differentiated. The utility of this technique to examine biological samples was shown by analysis of the fatty acid composition of cod liver oil. Detection limits for negative-ion ESI-MS/MS were at or below 1 pg.
130 citations
TL;DR: Lipophilic antioxidants BHA, BHT, and alpha-tocopherol were about 20 times more effective than hydrophilic free radical scavengers sodium benzoate, inositol, DMSO, and mannitol in preventing LOOH-induced strand breaks, supporting lipid phase localization of the damage.
117 citations
TL;DR: The relative stabilities of the R2XO, trans-RXOR, and cis-RxOR isomers were investigated by ab initio and DFT pseudopotential calculations as discussed by the authors.
Abstract: The relative stabilities of the R2XO, trans-RXOR, and cis-RXOR isomers (X = C, Si, Ge, Sn, Pb; R = H, CH3) were investigated by ab initio and DFT pseudopotential calculations. Geometry optimizations and frequency computations were performed at the MP2 and Becke3LYP levels with DZ+P basis sets. MP4SDTQ/(DZ+P)//MP2/DZ+P and CCSD(T)/(DZ+P)//MP2/DZ+P single point calculations gave high level ab initio data. The CCSD(T)/(DZ+P)//MP2/(DZ+P) and the Becke3LYP/(DZ+P) relative energies both agree and show that the C2v H2XO isomers (with the exception of formaldehyde) are the least stable and that the cis- and trans-HXOH Cs isomers are very close in energy. Acetone and dimethylsilanone are the most stable isomers in the Me2XO series. However, with the notable exception of HPbOH, the H2XO compounds are not stable thermodynamically toward cyclotrimerization or to hydration. The NPA/NLMO charges, bond orders, and orbital hybridizations support the polar description -O:::X+R2 of all metal “double bond” species. The -O::...
116 citations
TL;DR: A series of heterocyclic metal carbene complexes were prepared by the deoxygenation reaction of M(CO)6 (M = Cr, Mo, W) with RNH(CH2)nNPPh3 (R = H, Et, Ph; n = 2, 3, 4) as discussed by the authors.
112 citations
TL;DR: Kinetics of epoxidations of alkyl-substituted alkenes, with hydrogen peroxide as the oxygen source, suggest a concerted mechanism in which the electron-rich double bond of the alkene attacks a peroxidic oxygen of B.
Abstract: Epoxidations of alkyl-substituted alkenes, with hydrogen peroxide as the oxygen source, are catalyzed by CH(3)ReO(3) (MTO). The kinetics of 28 such reactions were studied in 1:1 CH(3)CN-H(2)O at pH 1 and in methanol. To accommodate the different requirements of these reactions, (1)H-NMR, spectrophotometric, and thermometric techniques were used to acquire kinetic data. High concentrations of hydrogen peroxide were used, so that diperoxorhenium complex CH(3)Re(O)(eta(2)-O(2))(2)(H(2)O), B, was the only predominant and reactive form of the catalyst. The reactions between B and the alkenes are about 1 order of magnitude more rapid in the semiaqueous solvent than in methanol. The various trends in reactivity are medium-independent. The rate constants for B with the aliphatic alkenes correlate closely with the number of alkyl groups on the olefinic carbons. The reactions become markedly slower when electron-attracting groups, such as halo, hydroxy, cyano, and carbonyl, are present. The rate constants for catalytic epoxidations with B and those reported for the stoichiometric reactions of dimethyldioxirane show very similar trends in reactivity. These findings suggest a concerted mechanism in which the electron-rich double bond of the alkene attacks a peroxidic oxygen of B. These data, combined with those reported for the epoxidation of styrene (a term intended to include related molecules with ring and/or aliphatic substituents) by B and by the monoperoxo derivative of MTO, suggest that all of the rhenium-catalyzed epoxidations occur by a common mechanism. The geometry of the system at the transition state can be inferred from these data, which suggest a spiro arrangement.
108 citations
TL;DR: The potential energy surface of the triatomic cation [Cr,O2]+ has been examined by means of ion-cyclotron resonance and sector-field mass spectrometry as well as high-level theoretical methods as mentioned in this paper.
Abstract: The potential-energy surface of the triatomic cation [Cr,O2]+ has been examined by means of ion-cyclotron resonance and sector-field mass spectrometry as well as high-level theoretical methods. Chromium(V) dioxide cation OCrO+ can be generated by electron ionization of CrO2Cl2 and exhibits a doublet ground state. The experimentally determined IE(CrO2) of 9.7 ± 0.2 eV leads to ΔHf(OCrO+) = 209 ± 12 kcal/mol which compares well with a theoretical prediction of 217 kcal/mol. The high-valent chromium(V) dioxide OCrO+ slowly reacts with H2 to form CrO+ and H2O as products. Activation of saturated and unsaturated hydrocarbons, including methane and benzene, is much more efficient and involves C−H as well as C-C bond activation. In the reaction of OCrO+ with CH4 the by-product OCr(OCH2)+ points to the operation of a stepwise mechanism in that initially a single oxo unit in OCrO+ is activated in terms of a [2 + 2] cycloaddition of methane across the Cr−O double bond. A structurally different [Cr,O2]+ cation can b...
104 citations
TL;DR: In this paper, the ruthenium complex (η5-C4Ph4COHOC 4Ph4-η 5)(μ-H)(CO)4Ru2 and its phenyl ring-substituted derivatives were found to act as efficient catalysts in reduction reactions of aldehydes and ketones to alcohols, using formic acid as H source.
99 citations
TL;DR: In this article, a regioselective formation of [60]fullerene derivatives with octahedral addition patterns is described via template activation with 9,10-dimethylanthracene Th-symmetric as well as mixed C2v-symetric hexaadducts.
TL;DR: High chemical yields, the simplicity of the experimental procedure, and the low cost of all reagents employed make this biomimetic transamination of fluorocarbonyl compounds a practical method for preparing fluorine-containing amines of biological interest.
Abstract: A systematic study of azomethine-azomethine isomerizations of the N-benzylimines 2, derived from fluorinated aldehydes or ketones and benzylamine, has been made. The results reveal that, in sharp contrast to hydrocarbon analogs, fluorinated imines of 2 in triethylamine solution undergo isomerizations to give the corresponding N-benzylidene derivatives 5 (for 5/2 K > 32) in good isolated yields. The rates of the isomerizations depend on the starting imine structures and increase in the following order: aryl perfluoroalkyl ketimine 2m, per(poly)fluoroalkyl aldimine 2a,d-g, perfluoroaryl aldimine 2h, alkyl perfluoroalkyl ketimine 2i,j. The presence of chlorine or bromine atoms in the alpha-position to the C=N double bond of the starting imine favors a dehydrohalogenation reaction, giving rise to unsaturated products 6-9. The azomethine-azomethine isomerization was studied and proven to proceed essentially (>98%) intramolecularly with isotope exchange experiments. High chemical yields, the simplicity of the experimental procedure, and the low cost of all reagents employed make this biomimetic transamination of fluorocarbonyl compounds a practical method for preparing fluorine-containing amines of biological interest.
TL;DR: In this article, the cross molecular beam technique was employed to investigate the reaction between ground state carbon atoms, C(3Pj), and allene, H2CCCH2(X 1A1), at two averaged collision energies of 19.6 and 38.8 kJ
Abstract: The crossed molecular beams technique was employed to investigate the reaction between ground state carbon atoms, C(3Pj), and allene, H2CCCH2(X 1A1), at two averaged collision energies of 19.6 and 38.8 kJ mol−1. Product angular distributions and time-of-flight spectra of C4H3 were recorded. Forward-convolution fitting of the data yields weakly polarized center-of-mass angular flux distributions isotropic at lower, but forward scattered with respect to the carbon beam at a higher collision energy. The maximum translational energy release and the angular distributions combined with ab initio and RRKM calculations are consistent with the formation of the n-C4H3 radical in its electronic ground state. The channel to the i-C4H3 isomer contributes less than 1.5%. Reaction dynamics inferred from the experimental data indicate that the carbon atom attacks the π-orbitals of the allenic carbon–carbon double bond barrierless via a loose, reactant-like transition state located at the centrifugal barrier. The initiall...
TL;DR: The reaction of ozone with phospholipids containing polyunsaturated fatty acyl groups is a useful method to probe the position of double bonds by electrospray ionization mass spectrometry.
Abstract: The reaction of ozone with double bonds present in glycerophosphocholine lipids results in formation of ozonides that can be directly analyzed by mass spectrometry as either positive or negative molecular ion species generated by electrospray ionization. Polyunsaturated fatty acyl groups esterified to the phospholipid yielded a mixture of ozonide species with the maximum number of ozone molecules added equal to the total number of double bonds. Ozonide decomposition resulted in ω-aldehyde and ω-carboxylic acid products as revealed by ESI-MS. Collisional activation of the ozone adducts for mono- and polyunsaturated phospholipids gave rise to fragment ions indicative of the position of the double bonds in these molecules. The major decomposition pathway for either positive or negative ozonide ion species involved charge remote fragmentation of the ozonide initiated by homolytic cleavage of the peroxide bridge followed by rearrangement to form the ω-aldehyde and ω-carboxylate acyl species. The reaction of oz...
TL;DR: In this article, a variety of terpenes bearing electron-withdrawing groups such as neryl acetate, geranyl acetate (4), citral (5), and geranyl nitrile (6) were epoxidized in preference to the others.
Abstract: Catalytic epoxidation of monoterpenes with aqueous hydrogen peroxide catalyzed by peroxotungstophosphate (PCWP) under biphase conditions using chloroform as the solvent was examined. A variety of terpenes was oxidized to the corresponding monoepoxides or diepoxides in good yields under mild conditions. For example, limonene (1) was converted into limonene oxide (1a) in which the cyclohexene double bond was selectively epoxidized in almost quantitative yield. The oxidation of γ-terpinene (2) with 2.2 equiv of 35% H2O2 took place with high stereoselectivity to give cis-diepoxide 2c. In terpenes bearing electron-withdrawing groups such as neryl acetate (3), geranyl acetate (4), citral (5), and geranyl nitrile (6), the double bonds remote from the substituents were epoxidized in preference to the others. The epoxidation of linalool (9) by the present catalyst−oxidant system produced the cyclic products, hydroxy furan 9a and hydroxy pyran 9b, rather than epoxide. tert-Butyl alcohol was successfully employed as...
TL;DR: A new turnover mechanism is proposed, not involving direct participation of the oxo ligand group, and based on that of Coucouvanis et al, to give a Mo(VI) species.
Abstract: The reaction mechanism of the molybdoenzyme xanthine oxidase has been further investigated by 13C and 17O ENDOR of molybdenum(V) species and by kinetic studies of exchange of oxygen isotopes. Three EPR signal-giving species were studied: (i) Very Rapid, a transient intermediate in substrate turnover, (ii) Inhibited, the product of an inhibitory side reaction with aldehyde substrates, and (iii) Alloxanthine, a species formed by reaction of reduced enzyme with the inhibitor, alloxanthine. The Very Rapid signal was developed either with [8-13C]xanthine or with 2-oxo-6-methylpurine using enzyme equilibrated with [17O]H2O. The Inhibited signal was developed with 2H13C2HO and the Alloxanthine signal by using [17O]H2O. Estimates of Mo-C distances were made, from the anisotropic components of the 13C-couplings, by corrected dipolar coupling calculations and by back-calculation from assumed possible structures. Estimated distances in the Inhibited and Very Rapid species were about 1.9 and less than 2.4 A, respectively. A Mo-C bond in the Inhibited species is very strongly suggested, presumably associated with side-on bonding to molybdenum of the carbonyl of the aldehyde substrate. For the Very Rapid species, a Mo-C bond is highly likely. Coupling from a strongly coupled 17O, not in the form of an oxo group, and no coupling from other oxygens was detected in the Very Rapid species. No coupled oxygens were detected in the Alloxanthine species. That the coupled oxygen of the Very Rapid species is the one that appears in the product uric acid molecule was confirmed by new kinetic data. It is concluded that this oxygen of the Very Rapid species does not, as frequently assumed, originate from the oxo group of the oxidized enzyme. A new turnover mechanism is proposed, not involving direct participation of the oxo ligand group, and based on that of Coucouvanis et al. [Coucouvanis, D., Toupadakis, A., Lane, J. D., Koo, S. M., Kim, C. G., Hadjikyriacou, A. (1991) J. Am. Chem. Soc. 113, 5271-5282]. It involves formal addition of the elements of the substrate (e.g., xanthine) across the Mo = S double bond, to give a Mo(VI) species. This is followed by attack of a "buried" water molecule (in the vicinity of molybdenum and perhaps a ligand of it) on the bound substrate carbon, to give an intermediate that on intramolecular one-electron oxidation gives the Very Rapid species. The latter, in keeping with the 13C, 17O, and 33S couplings, is presumed to have the 8-CO group of the uric acid product molecule bonded side-on to molybdenum, with the sulfido molybdenum ligand retained, as in the oxidized enzyme.
TL;DR: The [Rh2(OAc)4]-catalyzed decomposition of NsN(DouBLE BOND)IPh {N-(p-nitrobenzenesulfonyl)imino]phenyliodinane} in the presence of olefins affords aziridines in yields of up to 85%.
TL;DR: A linear solvation energy relationship has been found for 353 values of the limiting adsorption coefficients of diverse chemicals: log K = −0.37 + 0.0341Vi − 1.227V2/3 −1.65P with R = 0.51, n = 353, and F = 818 as mentioned in this paper.
Abstract: A linear solvation energy relationship has been found for 353 values of the limiting adsorption coefficients of diverse chemicals: log K = −0.37 + 0.0341Vi − 1.07β + D + 0.65P with R = 0.951, s = 0.51, n = 353, and F = 818.0, where Vi is the intrinsic molar volume; β is a measure of the hydrogen bond acceptor strength of the solute; D is an index parameter for the research group which includes the effects of the different types of carbon used, the temperature, and the length of time allowed for the adsorption equilibrium to be established; and P is an index parameter for the flatness of the molecule. P is defined to be unity if there is an aromatic system in the molecule or if there is a double bond or series of conjugated double bonds with no more that one non-hydrogen atom beyond the double bond and zero otherwise. A slightly better fit is obtained if the two-thirds power of Vi is used as a measure of the surface area in place of the volume term: log K = −1.75 + 0.227V2/3 − 1.10β + D + 0.60P with R = ...
TL;DR: Methyltrioxorhenium-catalyzed oxidation of sulfides with hydrogen peroxide in ethanol has been found to be an efficient catalytic system for the selective formation of sulfoxides and sulfones as discussed by the authors.
Abstract: Methyltrioxorhenium-catalyzed oxidation of sulfides with hydrogen peroxide in ethanol has been found to be an efficient catalytic system for the selective formation of sulfoxides and sulfones. The oxidation using an equimolar amount of hydrogen peroxide afforded sulfoxides in excellent yield, and the use of two molar amounts of hydrogen peroxide gave sulfones quantitatively. Strongly deactivated sulfide, bis(4-nitrophenyl) sulfide, was converted smoothly to the corresponding sulfoxide and sulfone in excellent yields. The functional group in the side chain of sulfide such as a carbon–carbon double bond was not affected under the reaction conditions, and the sulfur atom was selectively oxidized.
TL;DR: In this article, the effect of metal particle size on the catalytic activity and selectivity has been studied by using catalysts having a metal dispersion ranging from 0.05 to 0.88.
Abstract: The hydrogenation of citral and cinnamaldehyde has been investigated over Ru/Al 2 O 3 catalysts. The effect of metal particle size on the catalytic activity and selectivity has been studied by using catalysts having a metal dispersion ranging from 0.05 to 0.88. It has been observed that the overall rate of hydrogenation of both the unsaturated aldehydes is not influenced by the Ru particle size. In the hydrogenation of cinnamaldehyde a higher selectivity to cinnamyl alcohol has been observed on catalysts with larger metal particle size. No variations have been found in the hydrogenation of citral. It is suggested that steric effects do not influence significantly the product selectivity. A repulsive interaction between the aromatic ring and the catalyst surface would explain the higher selectivity to cinnamyl alcohol. On all the investigated catalysts the isolated C C double bond of citral shows a low reactivity. It is suggested that the unsaturated aldehyde is adsorbed through the carbonyl group. This strong adsorption prevents the hydrogenation of the isolated olefinic bond which is located far away from the adsorption centers.
TL;DR: In this paper, the influence of the electronegativity of the ligands Y (F, Cl, Br, I, OH, NH2, CH3, H) on the strength of the σ*-aromatic effect in gem-disubstituted 1H-Phosphirenium cations and substituted 3-silacyclopropenes has been investigated with ab initio theory.
Abstract: The influence of the electronegativity of the ligands Y (F, Cl, Br, I, OH, NH2, CH3, H) on the strength of the σ*-aromatic effect in gem-disubstituted 1H-Phosphirenium cations and substituted 3-silacyclopropenes has been investigated with ab initio theory. Phosphorus and silicon provide a low lying p-type σ*-orbital antibonding to the ligands Y. This interacts with the ring double bond analogously to a third p-orbital in a 2π Huckel system. These systems have been compared to the analogous saturated rings. Calculations at the RHF/6-31G* and MP4/6-31+G* levels, NBO analyses of the effect of the ligands Y and comparisons of the relative stabilities of the saturated and unsaturated compounds suggest a weak but significant σ*-aromatic effect dependent on the electronegativity of Y.
TL;DR: Deuterium isotope effects on 13C nuclear shielding, nΔC(OD), were investigated for a series of enolic β-diketones at different temperatures as discussed by the authors.
Abstract: Deuterium isotope effects on 13C nuclear shielding, nΔC(OD), were investigated for a series of enolic β-diketones at different temperatures. The investigated enolic β-diketones cover a broad range of tautomeric equilibrium constants (K). The equilibrium constants were estimated from 17O and 13C chemical shifts. 13C chemical shifts and the deuterium isotope effects show changes with temperature, which are due to a change in the tautomeric equilibrium. It is shown that the variation of K with deuterium substitution depends on K. This has the important consequence that the equlibrium isotope effects for a series with different K may go through a maximum. If the sum of the deuterium isotope effects on 13C chemical shifts for the carbonyl and enolic carbons is above 0.8 ppm for five-membered and 1.2 ppm for six-membered ring compounds, the system is tautomeric. This statement holds for sterically non-hindered compounds. The intrinsic two-bond deuterium isotope effects for an intramolecular hydrogen bonded system with a chelate six-membered ring with optimal geometry and a localized double bond are estimated to be 1.2 ppm. Knowing the intrinsic contribution, deuterium isotope effects can be used to estimate the position of tautomeric equilibria for β-diketones. 1H chemical shifts of OH groups display a linear relation with the molar fraction X.
TL;DR: In this article, the reactivity of different olefinic substrates is compared and is shown to be dependent on the structure, which allows the selective epoxidation of compounds containing different kinds of double bonds.
Abstract: Silica gel treated with Ti(OiPr)4 is an efficient catalyst for the TBHP epoxidation of non-functionalized alkenes, dienes, and allylic alcohols. This catalyst is more efficient than those obtained from other titanium precursors; it must be activated at 140°C prior to use, it can be recovered and stored in the open air. The reactivity of different olefinic substrates is compared and is shown to be dependent on the structure, which allows the selective epoxidation of compounds containing different kinds of double bonds.
TL;DR: In this paper, the adsorption of 1,3-butadiene and 1-butene on Pt(111), and Pd(111) was studied by near edge X-ray absorption fine structure (NEXAFS).
TL;DR: In this article, the retention properties of various benzyl, phenacyl, and normal-and branched-chain alkyl esters of 6-18:1, 9-18-1 and 11-18 :1 fatty acids have been studied by silver ion high-performance liquid chromatography.
TL;DR: A theoretical evaluation of tetra-tert-butylethylene (1) at the BLYP/DZd level confirms that it should be a stable molecule with a singlet ground state.
Abstract: A theoretical evaluation of tetra-tert-butylethylene (1) at the BLYP/DZd level confirms that it should be a stable molecule with a singlet ground state. The synthesis of 1 from two molecules of di-...
TL;DR: In this paper, all the reactions which involve the exocyclic double bond of alkylidenecyclopropanes in cycloaddition processes are dealt with.
Abstract: Alkylidenecyclopropanes are a peculiar class of olefinic compounds characterized by a high ring strain, but at the same time a sufficient stability to permit their use in organic synthesis. The strain associated with the structure of these compounds is in general responsible for the good reactivity of the carbon-carbon double bond, even in sterically encumbered substrates. The key role of these compounds in organic synthesis resides in the exclusive, and by far the most useful, possibility of the introduction of a cyclopropyl ring in a more complex molecule through reactions onto the exocyclic double bond. For this reason the investigations on the synthesis and reactivity of these compounds has exploded in the last decade. This article will deal with all the reactions which involve the exocyclic double bond of alkylidenecyclopropanes in cycloaddition processes. Albeit most of the reactions are true pericyclic cycloaddition processes, also those reactions which lead to cycles by stepwise processes will be reported with comments on the mechanism.
TL;DR: Consideration of the bilayer-to-hexagonal transition in terms of bending and interstitial energies provides a rationale for the relative values of T(H), which exhibits a minimum when the C=C is around position 9.
TL;DR: Arylation of 1-(methoxycarbonyl)-2,5-dihydropyrrole under standard Heck reaction conditions produces a mixture of compounds and the C-3 arylated enamides were converted further into the corresponding 3-arylpyrrolidines.
Abstract: Arylation of 1-(methoxycarbonyl)-2,5-dihydropyrrole under standard Heck reaction conditions produces a mixture of compounds. The olefin undergoes two types of palladium-catalyzed reactions: (a) arylation to provide C-3 arylated derivatives and (b) competing double bond isomerization. Addition of silver carbonate and thallium acetate fully suppressed the isomerization, and good yields of C-3 substituted compounds were achieved after arylation with aryl halides. With regard to aryl triflates as arylating agents, addition of lithium chloride was necessary to promote the Heck reaction. This additive excluded the use of silver and thallium salts, but high regioselectivity and good yields could be obtained by employing tri-2-furylphosphine as ligand. Arylation was rendered both regioselective and enantioselective (58% ee) with 1-naphthyl triflate as substrate utilizing a (R)-BINAP/thallium acetate combination. The C-3 arylated enamides were converted further into the corresponding 3-arylpyrrolidines.
TL;DR: In this article, the authors reviewed peroxide curing of diene elastomers and observed changes in crosslinking mechanisms at high dicumyl peroxide loading and high curing temperature.
Abstract: The scope of this paper is to review peroxide curing of diene elastomers. At high dicumyl peroxide loading and high curing temperature, changes in the crosslinking mechanisms were observed. Both Abstraction of allylic hydrogen and addition to the double bond can act as mechanisms of crosslinking. IR spectroscopy reveals a significant decrease in double bonds, and a new relaxation at temperatures above the Tg of the elastomers is present.