Showing papers on "Double bond published in 1995"

Organic Compounds Produced by Photolysis of Realistic Interstellar and Cometary Ice Analogs Containing Methanol

Abstract: The InfraRed (IR) spectra of UltraViolet (UV) and thermally processed, methanol-containing interstellar / cometary ice analogs at temperatures from 12 to 300 K are presented. Infrared spectroscopy, H-1 and C-13 Nuclear Magnetic Resonance (NMR) spectroscopy, and gas chromatography-mass spectrometry indicate that CO (carbon monoxide), CO2 (carbon dioxide), CH4 (methane), HCO (the formyl radical), H2CO (formaldehyde), CH3CH2OH (ethanol), HC([double bond]O)NH2 (formamide), CH3C([double bond]O)NH2 (acetamide), and R[single bond]C[triple bond]N (nitriles) are formed. In addition, the organic materials remaining after photolyzed ice analogs have been warmed to room temperature contain (in rough order of decreasing abundance), (1) hexamethylenetetramine (HMT, C6H12N4), (2) ethers, alcohols, and compounds related to PolyOxyMethylene (POM, ([single bond]CH2O[single bond](sub n)), and (3) ketones (R[single bond]C([double bond]O)[single bond]R') and amides (H2NC([double bond]O)[single bond]R). Most of the carbon in these residues is thought to come from the methanol in the original ice. Deuterium and C-13 isotopic labeling demonstrates that methanol is definitely the source of carbon in HMT. High concentrations of HMT in interstellar and cometary ices could have important astrophysical consequences. The ultraviolet photolysis of HMT frozen in H2O ice readily produces the 'XCN' band observed in the spectra of protostellar objects and laboratory ices, as well as other nitriles. Thus, HMT may be a precursor of XCN and a source of CN in comets and the interstellar medium. Also, HMT is known to hydrolyze under acidic conditions to yield ammonia, formaldehyde, and amino acids. Thus, HMT may be a significant source of prebiogenic compounds on asteroidal parent bodies. A potential mechanism for the radiative formation of HMT in cosmic ices is outlined.

Chiral Auxiliaries and Ligands in Asymmetric Synthesis

Abstract: Enantiomerically Pure Chiral Auxiliaries. Chiral Reagents. Chiral Catalysis and Catalysts Bearing Chiral Ligands. Asymmetric Deprotonations and Protonations. Alkylations and Related Reactions. Additions to C=O and C=N Double Bonds. Additions to Carbon--Carbon Double Bonds. Additions to Double Bonds Bearing Heteroatoms Oxidations of Sulfides and Selenides. Cycloadditions. Sigmatropic Rearrangements. Transition Metal Catalyzed Reactions. References. Index.

The phenyldimethylsilyl group as a masked hydroxy group

Abstract: A phenyldimethylsilyl group attached to carbon can be converted into a hydroxy group 1→5, with retention of configuration at the migrating carbon, by any of three main methods. The first involves protodesilylation, to remove the phenyl ring from the silicon atom, followed by oxidation of the resulting functionalised silicon atom using peracid or hydrogen peroxide. The second uses mercuric acetate for the same purpose, and can be combined in one pot with the oxidative step using peracetic acid. This method has a variant in which the mercuric ion is combined with palladium(II) acetate, both in less than stoichiometric amounts. The third uses bromine, which can also be used in one pot in conjunction with peracetic acid. In this method, but not in the method based on mercuric acetate, the peracetic acid may be buffered with sodium acetate. The method using bromine as the electrophile for removing the benzene ring has a more agreeable variant in which it is administered in the form of potassium bromide, which is oxidised to bromine by the peracetic acid. The scope and limitations of each of these methods are reported with a range of examples possessing between them many of the common functional groups. Simple benzene rings, alcohols, ethers, esters, amides and nitriles are compatible with all three methods, and ketones do not undergo Baeyer–Villiger reaction under any of the conditions. Amines, however, are oxidised to amine oxides. Ketones may be brominated in the third of the three main recipes. The absence of acid in the third method makes it especially valuable when the phenyldimethylsilyl group has a neighbouring nucleofugal group such as hydroxy or acetoxy. Carbon–carbon double bonds are incompatible with the methods, except for terminal monosubstituted double bonds, which can survive the conditions used in the first of the three methods.

Hydrocyanation process and multidentate phosphite and nickel catalyst composition therefor

Abstract: A process for hydrocyanation of an aliphatic monoethylenically unsaturated compound, in which the ethylenic double bond is not conjugated to any other unsaturated group in the molecule, or a monoethylenically unsaturated compound in which the ethylenic double bond is conjugated to an ester group, which process uses a catalyst composition comprising a zero-valent nickel and a multidentate phosphite ligand in the presence of a Lewis acid promoter.

Synthesis of Polyenes That Contain Metallocenes via the Living Polymerization of Ethynylferrocene and Ethynylruthenocene

Abstract: We describe the living polymerization of ethynylferrocene and ethynylruthenocene and the copolymerization of ethynylferrocene and TCDTF6 (TCDTF6 = 7,8-bis(trifluoromethyl)tricyclo[4.2.2.0 2,5 ]-deca-3,7,9-triene). In all cases Mo(N-2,6-Me 2 C 6 H 3 )(CHCMe 2 Ph)[OCMe(CF 3 ) 2 ] 2 was the initiator that was employed. Charged systems were generated by terminating the living polymer with pyridinecarboxaldehyde followed by quaternizing the tertiary nitrogen with methyl iodide. Polyenes and copolyenes that contain up to ∼50 double bonds are soluble. Charged polymers exhibit a more intense and red-shifted absorption. NMR studies suggest that ethynylferrocene adds to the initiator to give an unobservable intermediate α-substituted metallacyclobutene that opens to give the disubstituted (ferrocenyl/vinyl) propagating alkylidene. The structures of the first and second insertion products obtained by capping the chain with ferrocenecarboxaldehyde or pyridinecarboxaldehyde confirm that α addition takes place, a trans double bond is formed, and polymerization is virtually exclusively head-to-tail. Ethynylferrocene reacts extremely slowly with Mo(N-2,6-Me 2 C 6 H 3 )(CHCMe 2 Ph)(O-t-Bu) 2 via α addition and with Mo(NAr)-(CHCMe 2 Ph)(OC 6 F 5 ) 2 (quinuclidine) and Mo(NAd)(CHCMe 2 Ph)[OCH(CF 3 ) 2 ] 2 (2,4-lutidine) via β-addition.

About the aromaticity of five-membered heterocycles

Abstract: The aromaticity of five-membered heterocycles with one and two heteroatoms (O, S, NH, N and P) has been investigated, using energetic and structural criteria. It has been shown that to obtain a correct order for the aromaticity, a nonhomodesmic reaction (SEH) is sufficient, provided it compares the energy of the ring to that of the conjugated building blocks in the ring. Contrary to general expectations, superhomodesmic reactions seem less reliable owing to unpredictable steric interactions in the conjugated reference molecules. The stabilization shows a considerable increase if calculated at the MP2 versus HF level of theory in all reactions. The aromatic stabilization in the ring is mainly determined by the “first heteroatom” which provides two electrons for the π-system (O, S or NH). The effect of the second heteroatom is much smaller. In agreement with earlier observations, N as a second heteroatom increases the stabilization in the SEH reaction. In the case of P, stabilization has again been observed, but only at the MP2 level. An aromaticity index has been defined based on the double bond characters of the peripheral bonds in the ring. According to this geometry aromaticity index ( I ), there is no apparent increase in aromaticity for the phosphorus compounds; thus, I can be related to the decrease in ring strain, attributable to the small bonding angle about phosphorus.

High affinity and selectivity on 5-HT1A receptor of 1-aryl-4-[1-tetralin)alkyl]piperazines. 2.

Abstract: Several 4-alkyl-1-arylpiperazines that present a tetralin moiety on the terminal part of the side chain were synthesized in order to increase the selectivity on the 5-HT1A versus D-2, alpha 1, sigma, and other 5-HT receptors Many changes have been effected on previous structures of type 3(1-aryl-4-[3-(1,2-dihydronaphthalen-4-yl)-n-propyl]piperazines) Several synthetic procedures were followed to obtain the final products, depending on the presence or absence of a double bond, as well as of a heteroatom on the side chain In the first case versatile use of Grignard reaction was made, whereas in the second one usual synthetic ways were applied Final compounds were evaluated for in vitro activity on dopamine D-1 and D-2, serotonin 5-HT1A, 5-HT1B, 5-HT1C, and 5-HT2, alpha 1 adrenergic, and sigma receptors by radioreceptor binding assay For the 2-MeO-Ph, 2-pyridyl, and unsubstituted phenyl N-piperazine derivatives, low IC50 values (03 nM) on 5-HT1A receptors and high selectivity values were observed

ortho-Chelating Arenethiolatocopper(I) Complexes as Versatile Catalysts in the Regioselective Cross-Coupling of Allylic Derivatives with nBuMgI—An Example of Reversed Reactivity of Leaving Groups

Abstract: The regioselectivity in the arenethiolatocopper(I)-catalyzed crosscoupling reaction of allylic substrates was studied. It was found that allylic acetates gave highly γ-selective reactions in Et2O at 0°C with slow addition of the Grignard reagent, whereas α-selective reactions were obtained in THF at −30°C with fast addition of the Grignard reagent. It is proposed that the formation of an intermediate in Et2O, in which the allylic acetate coordinates in a bidentate fashion the arenethiolatocopper(I) catalyst, dramatically increases the reactivity of the leaving group and results in excellent γ-selectivity. The remarkable observation that an allylic acetate can be made more reactive than an allylic chloride by using the arenethiolatocopper(I) catalyst 1a supports the theory of a bidentate coordination of the substrate to the catalyst through its double bond and acetate oxygen.

Spectroscopy and photophysics of bridged enone derivatives: effect of molecular structure and solvent

Abstract: The spectroscopy and photophysics of several substituted enones with different bridged structures were studied in a variety of solvents. Results show that, in all cases, the non-radiative and radiative decay processes of the excited states are strongly influenced by the molecular structure and the solvent polarity. The “negative solvatokinetic effect” and “positive solvatokinetic effect” are observed for all four compounds. Compounds 3 and 4, with bridged double bond structures, have high fluorescence quantum yields and (especially compound 4 with a rigid structure even in non-polar solvents (cyclohexane, Φf=0.5)), indicating that radiative decay is predominant during the decay of the excited states of these compounds. In contrast, the enone compounds with a free double bond have very low fluorescence quantum yields, indicating that non-radiative decay is important for these compounds.

Ab initio study of styrene and β‐methyl styrene in the ground and in the two lowest excited singlet states

Abstract: The structure and vibrational frequencies of styrene and trans‐β‐methyl styrene in the lowest three singlet states (S0, S1, and S2) have been calculated using ab initio quantum chemical methods The frequencies are compared with experimental data obtained in the bulk and in a supersonic jet The calculation shows that in the ground state the molecules have a broad shallow potential as a function of the torsional angle, are essentially planar, but may be slightly bent In the S1 and S2 states, the molecules are planar; In S1, the main structural change is in the aromatic ring, that is somewhat expanded In S2, the C=C vinyl double bond elongates, while the C1—Cα single bond becomes shorter, bringing these two bonds to almost equal length Correlation diagrams connecting ground state vibrational modes with ones belonging to electronically excited states are given; they show that for many out‐of‐plane modes the vibrational frequencies decrease upon electronic excitation This is accounted for in terms of the

Covalent carbon nitride material comprising C2 N and formation method

Abstract: A nitride material comprises C 2 N. A method of forming a covalent carbon material includes forming an atomic nitrogen source, forming an elemental reagent source and combining the atomic nitrogen, elemental reagent to form the covalent carbon material and annealing the covalent carbon material. The elemental reagent is reactive with the atomic nitrogen of the atomic nitrogen source to form the covalent carbon material. Annealing the covalent carbon material produces the C 2 N. In one embodiment, essentially all carbon nitride chemical bonds are single or double bonds.

Proposed mechanism for the cytochrome P450-catalyzed conversion of aldehydes to hydrocarbons in the house fly, Musca domestica.

Abstract: Experiments were performed to elucidate the mechanism of hydrocarbon formation in microsomal preparations from the house fly, Musca domestica. Antibody to both house fly cytochrome P450 reductase and a purified cytochrome P450 (CYP6A1) from the house fly inhibited (Z)-9-tricosene (Z9-23:Hy) formation from [15,16-3H]-(Z)-15-tetracosenal (24:1 aldehyde). Chemical ionization-gas chromatography-mass spectrometry (CI-GC-MS) analyses of the n-tricosane formed by microsomal preparations from [2,2-2H2,2-13C]- and [3,3-2H2,3-13C]tetracosanoyl-CoA demonstrated that the deuteriums on the 2,2- and 3,3-positions were retained in the conversion to the hydrocarbon product. Likewise, CI-GC-MS analysis of the Z9-23:Hy formed from [1-2H]tetracosenal by microsomal preparations demonstrated that the aldehydic proton on the 1-carbon was transferred to the hydrocarbon product. Hydrogen peroxide, cumene hydroperoxide, and iodosobenzene were able to support hydrocarbon production from [3H]24:1 aldehyde in place of O2 and NADPH for short incubation times. From these data, a cytochrome P450 mechanism is proposed in which the perferryl iron-oxene, resulting from heterolytic cleavage of the O-O bond of the iron-peroxy intermediate, abstracts an electron from the C=O double bond of the carbonyl group of the aldehyde. The reduced perferryl attacks the 1-carbon of the aldehyde to form a thiyl-iron-hemiacetal diradical. The latter intermediate can fragment to form an alkyl radical and a thiyl-iron-formyl radical. The alkyl radical then abstracts the formyl hydrogen to produce the hydrocarbon and CO2.

Intermolecular C–H activation by reactive titanocene alkylidene intermediates

Abstract: Thermal α-H abstraction from (C5H4R)2Ti(CH2CMe3)2(R = H, Me) produces reactive titanocene neopentylidene intermediates under mild conditions, that can either be trapped with PMe3 to yield the alkylidene complexes (C5H4R)2Ti(CHCMe3)PMe3, or add C–H bonds of hydrocarbon substrates R′H (R′H = benzene, p-xylene) to the TiC double bond to produce (C5H4R)2Ti(CH2CMe3)R′; an alternative reaction pathway, insertion of the alkylidene moiety into the cyclopentadienyl C–C bond, has been observed in the presence of THF.

A carbene–stannylene adduct with a long tin–carbon double bond?

Abstract: Bis(2,4,6-triisopropylphenyl)stannylene, formed by thermolysis of the cyclotristannane 4, reacts with 4,5-dimethyl-1,3-diisopropylimidazol-2-ylidene to furnish the adduct 8; an X-ray structural analysis of this compound reveals the presence of a long tin–carbon ‘double bond’ with a length of 237. 9(5) pm and a distinctly pyramidal tin centre.

Atomic images of saturated and unsaturated fatty acids at liquid/graphite interface and difference of tunneling currents between them observed by scanning tunneling microscopy

Abstract: Structures of arachidic acid and elaidic acid molecules adsorbed onto a graphite substrate were investigated using a scanning tunneling microscope. The ordered arrangements of the molecules were observed with atomic resolution. The image of an arachidic acid molecule is composed of nineteen bright spots at the individual hydrocarbon groups in the alkyl chain and a dark region at the carboxyl group. The image of an elaidic acid molecule with an unsaturated hydrocarbon chain is similar to that of an arachidic acid molecule except for a much brighter spot at the double bond in the hydrocarbon chain. As a result, functional groups such as hydrocarbon chains, carboxyl groups and double bonds could be distinguished by the tunnel currents.

EP2 -receptor agonists as agents for lowering intraocular pressure

Abstract: The invention relates to (±) trans- 2-[-4(1-hydroxyhexyl) phenyl]-5-oxocyclopentaneheptanoicacid, and ester and unsaturated derivatives thereof, prostaglandin derivatives. More particularly, the present invention concerns compounds of formula (I), wherein the wavy bonds indicate the α or β configuration, the dashed bond represents either a single or double bond, which double bond may be a cis or trans double bond and R is a saturated or unsaturated acyclic hydrocarbon group having from 1 to about 20 carbon atoms, or -(CH2)mR1- wherein m is 0-10, and R1 is an aliphatic ring having from about 3 to about 7 carbon atoms, or an aryl or heteroaryl ring having from about 4 to about 10 carbon atoms and wherein the heteroatom is selected from the group consisting of N, O and S. The compounds of the present invention are potent ocular hypotensives, and are particularly suitable for the management of glaucoma.

Reaction products of polyisobutylenes and nitrogen oxides or mixtures of nitrogen oxides and oxygen and their use as fuel and lubricant additives

Abstract: The invention concerns reaction products of polyisobutylenes having an average polymerisation degree P of 10 to 100 and a proportion E of 60 to 90 % of double bonds which can be reacted with maleic acid anhydride, E corresponding to 100 % of the calculated theoretical value if each polyisobutylene molecule has a reactive double bond of this type, with nitrogen oxides or mixtures of nitrogen oxides and oxygen. These reaction products are suitable as fuel additives, in particular for spark-ignition engines, and as lubricant additives.

Cyclic ether compounds

Abstract: Compositions are disclosed comprising (a) a metal chelate wherein the metal is selected from the group consisting of europium, terbium, dysprosium, samarium osmium and ruthenium in at least a hexacoordinated state and (b) a compound having a double bond substituted with two aryl groups, an oxygen atom and an atom selected from the group consisting of oxygen, sulfur and nitrogen wherein one of the aryl groups is electron donating with respect to the other. Such composition is preferably incorporated in a latex particulate material. Methods and kits are also disclosed for determining an analyte in a medium suspected of containing the analyte. The methods and kits employ as one component a composition as described above.

End Groups in 1-Butene Polymerization via Methylaluminoxane and Zirconocene Catalyst

Abstract: Poly(1-butene) was obtained by polymerization of 1-butene at 100 o C using rac-(dimethylsilyl)bis(4,5,6,7-tetrahydro-1-indenyl)zirconium dichloride (1) as catalyst and methylaluminoxane (MAO) as cocatalyst. The product was characterized by NMR ( 1 H and 13 C), SEC, and vapor pressure osmometry (VPO). The molecular weight M n of the polymer was determined as 1910, 2025, and 2055 by SEC, VPO, and NMR, respectively. The poly(1-butene) is 84% isotactic and has high regioselectivity (ca. 95% 1,2-addition). Both saturated and unsaturated end groups were characterized by NMR. Vinylidene and trisubstituted double bonds comprise approximately 67% and 29%, respectively, of the unsaturated end groups with the remainder consisting of vinylene, vinyl, and tetrasubstituted double bonds. n-Butyl and sec-butyl groups constitute the saturated end groups in the approximate ratio 10:1. There is a slight excess of saturated end groups relative to unsaturated end groups. These results are discussed in terms of a reaction mechanism of initiation and propagation with various chain-transfer reactions (β-hydride transfers with and without rearrangement, transfer to aluminum, transfer to vinylidene end groups, and β-alkyl transfer)