Showing papers on "Double bond published in 1997"

Olefin metathesis and metathesis polymerization

Abstract: Preface. Abbreviations. Introduction: The Olefin Metathesis Reaction. Brief History. The Metal Carbene Mechanism. Equilibria and Stereoselectivity. Survey of Catalyst Systems: Group IV. Group V. GroupVI. Group VII. Group VIII. Photochemically Activated Catalysts. The Metal Carbene/Metallacyclobutane Mechanism: Evidence from Cross-Metathesis Reactions. Evidence from the Stereochemistry of Metathesis of Internal Olefins. Evidence from Ring-Opening Metathesis Polymerization (ROMP). Evidence from the reactions of Well-Defined Metal Carbene Complexes. Evidence from the Reactions of Metallacyclobutane Complexes. Evidence of Initiating Species in Systems with Non-Carbene Catalysts. Theoretical Treatments. Related Reactions: [2+2] Reactions Between Compounds Containing Multiple Bonds. Relationship to Ziegler-Natta Polymerization. Involvement of Three-Membered Ring Compounds in Metathesis Reactions. Ethene and Terminal Alkenes: Ethene. Propene. But-1-ene and its Derivatives. Pent-1-ene and its Derivatives. Hex-1-ene and its Derivatives. Higher Acyclic Terminal Alkenes. Acyclic Disubstituted and Trisubstituted Ethenes. Cis/trans Isomerization. Pent-2-ene and 4-Substituted Derivatives. Hex-2-ene and 4-Methylhex-2-ene.Hept-2-ene and Hept-3-ene. Higher Acyclic Internal Olefins. Stereoselectivity in the Metathesis of Acyclic Olefins. 1,1-Disubstituted Olefins. Trisubstituted Ethenes. Acyclic Functionalized Alkenes: Esters. Other Carbonyl-Containing Compounds. Ethers. Amines. Nitriles. Chlorides and Bromides. Sulfides and Sulfonates. Silancs and Germanes. Phospanes. Acyclic Dienes: Double Bonds Linked only by C Atoms. Double Bonds Linked by C and Si, Ge orSn Atoms. Double Bonds Linked by C and N Atoms. Double Bonds Linked by C, Si, and O Atoms. Divinylferrocene. Some Further Applications in Organic Synthesis. Copolymers by Metathesis Condensation. Cross-Metathesis Between Acyclic Compounds: Ethene.Propene. Butenes. Pentenes. Hexenes. Higher Olefins. Functionalized Olefins. Acetylenes: Metathesis Reactions Involving Total Cleavage of the C=C bond. Metathesis Reactions Involving Cleavage of Two of the thress C=C Bonds. Metathesis Reactions of Enynes and Dienynes. Other Metathesis Routes to Polyacetylenes. Ring-Opening Metathesis Polymerization: General Aspects: Thermodynamic Aspects. Efficiency of Initiation. The Use of Chain-Transfer Agents. Molecular Weight Distributions. Polymer Micostructure. Monocyclic Alkenes and Polyenes: Four-Membered Rings. Five-Membered Rings. Six-Membered Rings. Seven-Membered Rings. Eight-Membered Rings. Nine-Membered Rings. Ten-Membered Rings. Twelve-Membered and Other Rings. Polycyclic Alkenes: Monomers Containing a Fused Cyclobutene Ring. Monomers Containing a Fused Cyclopentene Ring and One Double Bond. Monomers Containing a Fused Cyclopentene Ring and More than One Double Bond. Bicyclo[2.2.1] Compounds Containing Heteroatoms in the Ring System. Other Bicyclic Compounds. Copolymers of Cycloalkenes: Direct Metathesis Copolymerization. Cyclic Co-Oligomers. Block Copolymers by Sequential Addition of Monomers to Living Systems. Block Copolymers by Modification of Homopolymers. Comb and GraftCopolymers. Copolymers by ROMP in Conjunction with Radical Reactions. Cross-Metathesis Between Cyclic and Acyclic Olefins: End-Groups and Telomers. Dependence of Molecular Weight on [M 2]/[M 1]. Kinetic Data. Degradation of UnsaturatedPolymers by Metathesis: Degradation by Intramolecular Metathesis. Applications of the Olefin Metathesis Reaction: The Phillips Triolefin Process. The Neohexene Process. The Shell Higher Olefins Process. Other Multistage Processes Involving Metathesis. The Isoamylene Process. (Circle around alpha and omega) ((-Diolefins. trans-Poly(1-Pentenylene). trans-Poly(1-octenylene). Polymers of Norhornene. Polymers of Norbornene Derivatives. Miscellaneous. Bibliography. Subject Index.

Structural Requirements for Binding of Anandamide-Type Compounds to the Brain Cannabinoid Receptor

Abstract: In order to establish the structural requirements for binding to the brain cannabinoid receptor (CB1), we have synthesized numerous fatty acid amides, ethanolamides, and some related simple derivatives and have determined their Ki values. A few α-methyl- or α,α-dimethylarachidonoylalkylamides were also examined. In the 20:4, n-6 series, the unsubstituted amide is inactive; N-monoalkylation, at least up to a branched pentyl group, leads to significant binding. N,N-Dialkylation, with or without hydroxylation on one of the alkyl groups, leads to elimination of activity. Hydroxylation of the N-monoalkyl group at the ω carbon atom retains activity. In the 20:x, n-6 series, x has to be either 3 or 4; the presence of only two double bonds leads to inactivation. In the n-3 series, the limited data reported suggest that the derived ethanolamides are either inactive or less active than comparable compounds in the n-6 series. Alkylation or dialkylation of the α carbon adjacent to the carbonyl group retains the level...

4-aminoquinazoline derivatives

Abstract: Disclosed are novel 4-aminoquinazoline derivatives of the formula (See formula I) (wherein Z is NR3R4 in which R3 is H and R4 is Q2 or phenyl substituted with (R5)q or Z is (See formula II) the dotted line represents an optional double bond; R5 is a substituent such as halo, amino, alkyl, alkoxy, etc.; R6 is a substituent such as hydroxyl, amino, sulfo, alkoxy, carboxyl, etc.; q is 0-3; o is 0-2; Q2 is a 9- or 10-membered bicyclic heterocyclic moiety; Q1 is Ar-Y-X in which Ar is mono- or bicyclic (hetero)aryl, X is alkenylene, alkynylene or bond and Y is (CH2)p where p is 0-5; R1 is a substituent such as trifluoromethyl; n is 0-3; m is 1-2) and their pharmaceutically acceptable salts. Those compounds and the salts are useful for the treatment of hyperproliferative disorders and conditions in mammals.

Compounds Containing Planar‐Tetracoordinate Carbon

Abstract: It is a great challenge to synthesize compounds containing planar-tetracoordinate carbon that are stable enough to be isolated, investigated, and handled under ambient conditions. There have therefore been many attempts to construct hydrocarbon frameworks that can incorporate and stabilize tetravalent carbon in this “unnatural” planar coordination geometry, for example, by steric constraints. However, success is apparently more readily achieved if the “square Planar” carbon atom is stabilized electronically. Planar-tetracoordinate carbon is sp2-hybridized and has an electron deficient σ system. The p orbital orthogonal to the bonding plane is occupied by two electrons. Therefore, σ-donor/π-accptor substituents—that is, many metals—are in principle able to stabilize this “unnatural” geometry of tetravalent carbon. Meanwhile, well-established procedures for synthesizing very stable “anti-van't Hoff/LeBel compounds” have been devised, in which the planar-tetracoordinate carbon atom is stabilized, usually by the combined action of two directly bonded metals. In most cases, the square-planar carbon is part of a double bond system. Typical stabilizing metal combinations are Zr/Al or Zr/B, but there are also examples containing two transition metals from the right-hand side of the periodic table. Reliable estimates for the energy of stabilization of square planar carbon in such compounds are now available. Both theoretical and experimental investigations show that square planar carbon atoms that are stabilized by Zr/Zr+ and Zr/Al in dimetallic compounds are favored by about 12 and 40 kcalmol−1, respectively, over the trigonal planar alternatives. Square planar coordinated carbon is thus no longer an unusual feature in organometallic chemistry and must now be more frequently considered as an alternative structural possibility.

Synthesis and characterization of a stable dibismuthene : Evidence for a Bi-Bi double bond

Abstract: Treatment of an overcrowded triselenatribismane, 2,4,6-tris(bis(trimethylsilyl)methyl)phenyl-1,3,5-triselena-2,4,6-tribismane, with hexamethylphosphorous triamide in toluene at 100°C resulted in the quantitative formation of a stable dibismuthene [TbtBi=BiTbt, where Tbt is 2,4,6-tris(bis(trimethylsilyl)methyl)phenyl], a compound containing a double bond formed between two bismuth atoms. The compound formed as deep purple crystals upon cooling. Ultraviolet-visible and Raman spectra, x-ray crystallographic structural analysis, and theoretical calculations provided evidence for the double bond character of the Bi–Bi bond.

Carbene-Pnictinidene Adducts

Abstract: The syntheses, characterizations, and X-ray crystallographic structure determinations are described for adducts of stable nucleophilic carbenes with pnictinidenes. The adducts between 1,3-dimesitylimidazol-2-ylidene and phenylphosphinidene, phenylarsinidene, (trifluoromethyl)phosphinidene, and (pentafluorophenyl)arsinidene are reported. These carbene-pnictinidene adducts are formed by the direct reaction of a stable nucleophilic carbene with the corresponding pnictinidene cyclic oligomers. The synthesis and structure of the adduct between 1,3-dimesitylimidazolin-2-ylidene and phenylphosphinidene from the reaction of 1,3-dimesitylimidazolin-2-ylidene with phenylphosphorus dichloride are also reported. These carbene-pnictinidene adducts possess strongly polarized pnictinidene-carbene bonds. The C-Pn-C angles are all typically small at 97-102 degrees, and there is only a 4% shortening of the nominal Pn=C double bond compared to the Pn-C single bond to the second substituent on the pnictogen. The (31)P NMR shifts of the phosphorus adducts suggest strongly shielded phosphorus centers in accord with the polarized structures.

Substituted 6,5-hetero-bicyclic derivatives

Abstract: This invention relates to compounds of formula (I), wherein the dashed lines represent optional double bonds; A is nitrogen or CR7; B is -NR?1R2, -CR1R2R10-C(=CR2R11)R1, -NHCR1R2R10, -OCR1R2R10, -SCR1R2R10, -CR2R10NHR1, -CR2R10OR1, -CR2R10SR1? or -COR2; J and K are each independently nitrogen or carbon and both J and K are not nitrogens; D and E are each selected, independently, from nitrogen, CR4, C=O, C=S, sulfur, oxygen, CR?4R6 and NR8?; G is nitrogen or carbon; and their use for the prevention or inhibition of a disorder that can be treated by antagonizing CRF.

Structure and Bonding of Ordered Organic Monolayers of 1,5-Cyclooctadiene on the Silicon(001) Surface

Abstract: The interaction of 1,5-cyclooctadiene with the (001) surface of silicon has been investigated using scanning tunneling microscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and ab initio computational chemistry techniques. Scanning tunneling microscopy images reveal that 1,5-cyclooctadiene molecules adsorb onto well-defined lattice sites and that the molecules are highly ordered both translationally and rotationally. Fourier-transform infrared and X-ray photoelectron spectra show that bonding occurs without dissociation by breaking one π bond of the 1,5-cyclooctadiene molecule and the π bond of one SiSi dimer of the reconstructed Si(001) surface, forming two new Si−C bonds. Only one of the two unsaturated bonds in each 1,5-cyclooctadiene molecule react, leaving one double bond exposed at the outermost surface. Computational chemistry studies suggest that the surface-bound molecule involves rapid interconversions of several similar low-symmetry conformations.

A Stereospecific Access to Allylic Systems Using Rhodium(II)−Vinyl Carbenoid Insertion into Si−H, O−H, and N−H Bonds

Abstract: Rhodium-catalyzed decomposition of α-vinyldiazoesters in the presence of silanes, alcohols, ethers, amines, and thiols have been shown to produce the corresponding α-silyl, α-hydroxy, α-alkoxy, α-amino, and α-thioalkoxy esters in generally good yield with a complete retention of the stereochemistry of the double bond of the diazo precursor. An extension of the process in homochiral series has also been devised using either a chiral auxiliary attached to the ester function or achiral α-vinyldiazoesters and Doyle's chiral catalyst Rh2(MEPY)4. In the former approach, pantolactone as chiral auxiliary gave diastereoselectivities of up to 70%, while the second approach produced the desired allylsilane with ee as high as 72%. On the other hand, Rh2(MEPY)4-catalyzed insertion into the O−H bond of water led to poor or no enantioselectivity in good agreement with recent literature reports.

New Methods of Free-Radical Perfluoroalkylation of Aromatics and Alkenes. Absolute Rate Constants and Partial Rate Factors for the Homolytic Aromatic Substitution by n-Perfluorobutyl Radical.

Abstract: New methods of free-radical perfluoroalkylation of aromatics and alkenes are reported. n-C4F9I has been utilized as source of C4F9• radical through iodine abstraction by phenyl or methyl radical. The reaction with alkenes, carried out in the presence of catalytic amount of Cu(OAc)2, leads to substitution by a mechanism substantially identical to the aromatic substitution and not to the usual chain addition of perfluoroalkyl group and iodine atom to the double bond. This has allowed to measure for the first time the absolute rate constants and the partial rate factors for the homolytic aromatic perfluoroalkylation by competition kinetics. The C4F9• radical shows a clear-cut electrophilic character in the aromatic substitution, as already reported for the addition to alkenes, but the low regio- and chemoselectivities suggest that the polar effect is not the main factor in determining the high reactivity of perfluoroalkyl radicals toward aromatics (105−106 M-1 s-1, 2−3 orders of magnitude more reactive than ...

Structure and Reactivity of Chelating Imido−Amido Complexes of Tantalum. Mechanistic Studies on the Addition of Silanes to Ta−N Multiple Bonds

Abstract: The synthesis, structural characterization, and reactivity of tantalum complexes with chelating imido−amido ligands are reported. The highly bent imido Cp* = η5-C5Me5), with a TaN−C bond angle of 116.3(4)°, was synthesized from Cp*TaCl4 and the lithiated bis(silylamino)biphenyl (C6H3Me)2(NLiSiMe3)2 (3). Compound 4 undergoes reactions with electrophiles at the nucleophilic imido nitrogen atom. The methyl reacts with xylyl isonitrile to give an insertion product, 6, which was structurally characterized. Addition of MeI to 5 gives a cationic diamide tantalum the ionic structure of which was confirmed by X-ray crystallography. Reactions of 4 and 5 with unhindered silanes result in addition of the silane Si−H bond across the TaN double bond. Addition of PhSiH3 to 4 and 5 gave the respectively. The crystal structure of 9 was determined. Compounds 8 and 9 are unstable and decompose via elimination of HSiMe3. In the presence of CH2Cl2 and PhSiH3, 4 was slowly converted to another hydrido A mechanism for this tran...

Dimers and Model Monomers of Nickel(II) Octaethylporphyrin Substituted by Conjugated Groups Comprising Combinations of Triple Bonds with Double Bonds and Arenes. 1. Synthesis and Electronic Spectra

Abstract: Porphyrin dimers linked in the meso-positions by bridges containing alkynes conjugated with the porphyrin π-systems display highly perturbed electronic absorption spectra. We have prepared a series...

The Addition of Malonates to Glycals: A General and Convenient Method for the Synthesis of 2-C-Branched Carbohydrates

Abstract: A general and convenient synthesis of carbohydrate 2-C-analogs by addition of malonates to glycals is described. The method is applicable to glycals derived from hexoses and pentoses and is characterized by easily available precursors. The reactions are mediated by manganese(III) or cerium(IV) and proceed via intermediarily generated malonyl radicals. All additions exhibit a very high degree of regioselectivity, since only 2-C-branched sugars were obtained. This result can be best rationalized by favorable orbital interactions between the SOMO of the malonyl radical and the HOMO of the double bond. Variation of the steric demand of the malonate or the glycal allows the stereoselectivities to be increased up to >98%. Highest selectivities were obtained with tri-O-acetyl-d-galactal and di-O-acetyl-d-arabinal, where the attack occurs exclusively from one face of the carbohydrate. For all cerium(IV)-mediated reactions, methyl glycosides are formed as main products in 73−89% yield, which can be isolated in ana...

The chemistry of pseudomonic acid. 18. Heterocyclic replacement of the alpha,beta-unsaturated ester: synthesis, molecular modeling, and antibacterial activity.

Abstract: The electronic requirements around the C1-C3 region of pseudomonic acid analogues were investigated. Synthetic routes were developed to access a range of compounds where the alpha, beta-unsaturated ester moiety had been replaced by a 5-membered ring heterocycle. The inhibition of isoleucyl tRNA synthetase from Staphylococcus aureus NCTC 6571 was determined as was the minimum inhibitory concentration (MIC) of the test compounds against that organism. Compounds possessing a region of electrostatic potential corresponding to that of the carbonyl group in the alpha, beta-unsaturated ester, and a low-energy unoccupied molecular orbital in the region corresponding to the double bond, were found to have IC50 values of 0.7-5.3 ng mL-1. However the MIC values of these compounds were in the range 2.0-8.0 micrograms mL-1, reflecting their poorer penetration into the bacterial cell.

Oxidation catalysis with semi-inorganic zeolite-based Mn catalysts

Abstract: The chelation of zeolite-exchanged Mn 2+ by N-containing ligands gives rise to a whole class of heterogeneous liquid phase oxidation catalysts. Bi-, tri- or tetradentate ligands can be used. A high degree of metal complexation is required to avoid side reactions due to the presence of zeolite-coordinated manganous ions. Applied physico-chemical techniques include IR, ESR and electronic spectroscopy. Oxidation-resistant chelands, e.g. with aromatic pyridine groups, are employed to ensure long-term catalyst stability. Use of hydrogen peroxide is most successful in combination with 2,2′-bipyridine (bpy) or 1,4,7-trimethyl-1,4,7-triazacyclononane (tmtacn); with both systems double bond oxidation proceeds with high selectivity. Olefin oxidations with other oxidants, e.g. tert -butylhydroperoxide ( t BuOOH) or iodosylbenzene, are less selective or slower. Alkane oxidation with t BuOOH is possible with various tetradentate diimine ligands. A principal effect of the zeolite matrix is that formation of Mn clusters is impeded in comparison with solution chemistry. Other effects of the zeolite matrix include modulation of the acid strength and suppression of side reactions, such as allylic oxidation of olefins or formation of isomerized epoxides.

Ingold−Fischer “Persistent Radical Effect”, Solvent Effect, and Metal Salt Oxidation of Carbon-Centered Radicals in the Synthesis of Mixed Peroxides from tert-Butyl Hydroperoxide

Abstract: Mixed peroxides are formed from tert-butyl hydroperoxide (TBH), tert-butyl peroxalate (TBP), and a variety of substrates (p-cresol, cyclohexene, styrene, α-methylstyrene, acrylonitrile, 2-methylcyclohexanone). Also, the oxidation of THF in the presence of acrylonitrile under the same conditions gives the mixed peroxide, generated by addition of the tetrahydrofuranyl radical to the double bond and the cross-coupling of the radical adduct with the tert-butylperoxyl radical. Similarly, benzoyl peroxide, TBH, and acrylonitrile give the mixed peroxide by oxidative arylation of the double bond. Paradoxically, TBH acts as effective inhibitor of the polymerization of vinyl monomers (acrylonitrile, styrene). An overall kinetic evaluation suggests that the conditions for the Ingold−Fischer “persistent radical effect”, characterized by the simultaneous formation of a persistent and a transient radical, are fulfilled in all cases. The reactions are strongly affected by solvents, which form hydrogen bonds with TBH. Ca...

Carbenoid Complexes of Electron‐Deficient Transition Metals—Syntheses of and with Short‐Lived Building Blocks

Abstract: The relation of thermodynamic stability and kinetic lability of σ-organometallic compounds of transition metals, together with an improved understanding of the subtle interactions between central metal, ligands, and substrates, has increased the chemist's ability to plan organometallic syntheses. This article presents new results on intermediary and isolable synthetic building blocks incorporating metal–ligand multiple bonds of electron-deficient transition metals; the main emphasis will be placed on compounds with titanium–carbon double bonds. This particular class of compounds is mainly generated by H-transfer reactions starting from readily accessible alkyl and alkenyl derivatives. The preparative use of [L2Ti(CHR2)R′] derivatives as sources for [L2TiCR2] intermediates will be discussed, as well as the nature of these intermediates. Application of the same approach to vinyltitanium compounds [L2Ti(CHCH2)R] opens up an access to a short-lived metallaallene derivative [L2TiCCH2] of an electron-deficient transition metal. The reactivity of these synthetic building blocks is mainly characterized by the nucleophilic properties of the α-C atoms as well as by the spatial orientation of the π-bonding planes. Numerous cycloaddition products with unsaturated substrates could be isolated and characterized for the first time by using [L2TiCCH2] intermediates. Hence it is possible to compare the properties of a multitude of metallacyclic ring systems with those obtained from “Tebbe–Grubbs chemistry”, and in this context, the dependence of the properties of metallacyclic four-membered rings on the substitution pattern is discussed. This class of compounds includes the metallaoxetanes, which have been obtained for the first time by the cycloaddition of the [CpTiCCH2] intermediate with cumulenes and metal carbonyls. The differing cycloreversion behavior of these metallaoxetanes enables the differentiation of species exhibiting classical and nonclassical reactivity. The number and position of the exocyclic double bonds are the determining factors of the reactivity of the formed metallacycles. The discussion of the products obtained from titanium methylene and vinylidene building blocks is an up-to-date report on the formation and applications of carbene complexes and carbene intermediates of group 4 metals.

Palladium-Catalyzed Cyclocarbonylation of Terminal and Internal Alkynols to 2(5H)-Furanones

Abstract: A series of substituted alkynols, containing alkyl, phenyl, and vinyl groups at the acetylenic terminal, were found to undergo direct carbonylation to the corresponding substituted 2(5H)-furanones in 67−98% yield. This reaction requires catalytic quantities of Pd2(dba)3·CHCl3 (4 mol %) and 1,4-bis(diphenylphosphino)butane (dppb) (8 mol %) in dichloromethane under an atmosphere of CO (600 psi) and H2 (200 psi) at 95 °C for 36 h. Hydrogen is required for this reaction. Another bidentate ligand such as 1,3-bis(diphenylphosphino)propane, and a monodentate ligand such as PPh3 or PCy3, are equally effective for this reaction. Conjugated ene−ynols can also be carbonylated affording 3-alkenyl-2(5H)-furanones in good yield. However, double bond isomerization (cis−trans) occurred if an ene−ynol containing a cis olefinic substituent was used as the substrate. The cyclocarbonylation reaction is believed to proceed via an allenylpalladium intermediate, which is formed by initial insertion of Pd(0) into the C−O bond of...

Pyrrolopyrimidines and processes for their preparation

Abstract: There are described compounds of formula (I) wherein R1 and R2 are as defined in the description, Q is heterocyclyl bonded via a ring nitrogen atom and having formula (IA) wherein R3 and R4 and m and n are as defined in the description, the ring marked A is a heterocyclyl having from 5 to 9 ring atoms and having at least one saturated bond, it being possible for a further ring hetero atom selected from O and S to be present in addition to the bonding nitrogen atom, the ring system marked B is a free or benzo-, thieno-, furo-, pyrrolo- or dihydropyrrolo-fused carbocyclic ring having from 5 to 9 carbon atoms that is fused to the ring A and may be unsaturated, partially saturated or fully saturated, and the bond marked by a parallel dotted line between the ring systems marked A and B is either a single bond or a double bond, and a salt thereof where at least one salt-forming group is present. The compounds are inhibitors of protein kinases and have, for example, antitumour activity.

Photophysics of 4-dimethylamino 4′-cyanostilbene and model compounds: dual excited states revealed by sub-picosecond transient absorption and Kerr ellipsometry

Abstract: 4-Dimethylamino 4′-cyanostilbene (DCS) and two selectively bridged compounds are investigated using sub-picosecond time-resolved absorption and Kerr ellipsometry experiments. The latter technique makes it possible to work at low excitation energy and low concentrations, thereby avoiding intensity and concentration effects which exist in DCS derivatives. Using this technique, in a non-polar solvent (cyclohexane), only the presence of a single excited state is observed for all studied compounds. In polar solvents, the bridged derivative where twisting of the anilino moiety is prevented but double bond twisting is allowed also reveals the presence of only one excited state. On the other hand, in polar solvents, for the DCS compound and the related bridged derivative where the anilino moiety is still able to twist, a precursor-successor relationship is clearly observed between two different excited states. These results can be understood within a four excited states model derived from a previously suggested diagram: the DE state (delocalized excited state), the ICT state (internal charge transfer, highly polar, nearly planar configuration, formed quasi-instantaneously from the DE state by electronic reorganization), the CRICT state (conformational relaxed ICT state, highly polar and fluorescent, involves conformational geometric changes such as twisting of the anilino group which enhances charge transfer) and the “phantom” state P∗ on the trans⇄cis isomerization pathway (twisted double bond, low polar, non-fluorescent). In this study, we observed the formation of the CRICT excited state on a time scale ranging from 2 to 20 ps depending on the solvent characteristics (polarity, viscosity and hydrogen bonding ability).

Trans Fatty Acids, Plasma Lipid Levels, and Risk of Developing Cardiovascular Disease : A Statement for Healthcare Professionals From the American Heart Association

Abstract: Dietary guidelines for the general population and individuals with hyperlipidemia specify upper limits for total fat, saturated fat, and cholesterol intake.1 2 The term trans fatty acids does not appear in dietary guidelines or on nutrient labels; however, it appears frequently in the scientific and lay press. Current issues of controversy are whether trans fatty acids should be listed on nutrient labels and whether this is the appropriate time to issue public health guidelines with respect to intake. Trans fatty acids contain at least one double bond in the trans configuration. The carbon/carbon double bonds of fatty acids can exist in either the cis or trans configuration. When the two hydrogen atoms are on opposite sides of the double bond, the configuration is termed trans ; when the two hydrogen atoms are on the same side of the double bond, the configuration is termed cis . Lack of rotational mobility precludes interconversion of configurations under normal circumstances. The bond angle is larger for a trans than a cis double bond. Therefore, the presence of a trans , relative to a cis , double bond results in acyl chains that can pack together more tightly. Trans double bonds occur in nature as such. They are the result of anaerobic bacterial fermentation in ruminant animals and are thereby introduced into the food chain.3 Humans consume them in the form of meat and dairy products. Trans double bonds are also formed during the hydrogenation of either vegetable or fish oils. Oils are hydrogenated to increase their plasticity and chemical stability, hence their potential use in food products. It is important to note that hydrogenation results in a number of changes in the acyl chain of the fatty acid moiety, all of which can impact physiological parameters: conversion of cis to trans …

Synthesis and Nonlinearity of Triene Chromophores Containing the Cyclohexene Ring Structure

Abstract: A series of conjugated donor−acceptor trienes in which the central double bond is incorporated into an unsaturated isophorone, verbenone, or chromone ring has been synthesized. In each case, the donor group consists of an amine and an aromatic or heterocyclic ring system, and the acceptor is the dicyanomethylidene group. The nonlinear optical properties of each of the compounds has been measured and correlated with its structure. The dipole moments and molecular hyperpolarizabilities of these compounds, like those of other conjugated polyenes, are large enough to be used as the active components of electrooptic polymers. Unlike other donor−acceptor polyenes, however, these compounds exhibit the thermal stability required for such applications.