Showing papers on "Double bond published in 1982"

1,4-Diaza-1,3-butadiene (a-diimine) ligands: their coordination modes and the reactivity of their metal complexes

Abstract: Publisher Summary Molecules containing the 1,4-diaza-1,3-butadiene skeleton have attracted much interest because of both their versatile coordination behavior and the interesting properties of their metal complexes. 1,4-diaza-1,3-butadienes (R-DAB) may be prepared by condensation reactions involving glyoxals, α-ketoaldehydes or α, β-–diketones with primary amines RNH2. It was concluded from nuclear magnetic resonance (NMR) spectra, dipole moments, and infrared (IR) spectra that the R-DAB molecule exists in solution in the E configuration at both C=N double bonds while the conformation of the central C–C bond is predominantly s-trans. So far stable complexes containing monodentate R–DAB have only been reported for the square planar d8–metals Pd11, Pt11, and Rh1. The reports of metal complexes with R–DAB ligands date back to 1953 when Krumholz described the synthesis of some ferrous complexes. The unusual stability and characteristic color being ascribed to the presence of π bonding between the metal and the nitrogen atoms. Factors, such as the substituents R and R, the metal atom, and the other ligands bonded to the metal atom, will influence the type of coordination of the R–DAB( R’,R) ligands. Just as 2, 2’-bipyridine, the R–DAB ligands can be readily converted to stable paramagnetic radical anions by potassium in 1,2-dirnethoxyethane or tetrahydrofuran (THF).

Factors affecting the quantity of remaining double bonds in restorative resin polymers

Abstract: The quantity of remaining unreacted double bonds may be a significant factor pertaining to the mechanical, physical and chemical properties of restorative resins. The said quantity was determined from the transmission IR-spectrum of the materials before and after polymerization. For proprietary resins the quantity of remaining double bonds was found to vary between 23 and 43%. For experimental, chemically cured resins the quantity in question was found to decrease with increasing resin content of amine and peroxide, and to increase with the content of inhibitor. The content of peroxide was the more influential of the three factors. For constant content of amine, peroxide, and inhibitor the number of remaining double bonds decreased with increasing content of diluting monomer in BISGMA-based monomer mixtures. The use of a trifunctional monomer as diluting monomer did not give rise to a higher degree of conversion of the double bonds in comparison to a bifunctional diluting monomer. The quantity of remaining double bonds of a light curing material was relatively small when compared to the quantity present in chemically cured materials of adequate setting time.

REACTIONS OF ALLYLSILANES AND APPLICATION TO ORGANIC SYNThESIS

Abstract: — Allylsilanes undergo regiospecific reactions with a variety of electrophilic species, especially with carbon electrophiles to form a new carbon—carbon bond. An electrophile enters on the terminus of the allylic system and the cleavage of the carbon—silicon bond occurs to give a new allylic system in which the double bond is relocated adjacent to its original position. Allylsilanes also undergo conjugate addition to n,3—eno— nes to give 6,c—enones exclusively. High nucleophilicity of the double bond of allylsilanes together with these advantageous features render very useful applications in organic synthesis.

Psoralen-deoxyribonucleic acid photoreaction. Characterization of the monoaddition products from 8-methoxypsoralen and 4,5'8-trimethylpsoralen.

Abstract: The isolation and structural characterization are described of the major monoaddition products formed in the photoreaction of two naturally occurring psoralens, 8-methoxypsoralen and 4,5',8-trimethylpsoralen, with high molecular weight, double-stranded DNA. Hydrolysis of the psoralen-modified DNA and subsequent chromatography resulted in the isolation of four modified nucleosides from each psoralen. Structural characterization was accomplished by mass spectrometry and 1H NMR analysis. The major products, accounting for 44-52% of the covalently bound psoralen, are two diastereomeric thymidine adducts formed by cycloaddition between the 5,6 double bond of the pyrimidine and the 4',5' (furan) double bond of the psoralen. A minor product, less than 2% of the covalently bound psoralen, is a furan-side adduct to deoxyuridine, derived from an initially formed deoxycytidine adduct by hydrolytic deamination. A fourth product is a thymidine adduct where cycloaddition has taken place between the 5,6 double bond of the pyrimidine and the 3,4 (pyrone) double bond of the psoralen. This pyrone-side adduct accounts for 19% of the covalently bound 8-methoxypsoralen but for less than 3% of the covalently bound 4,5'8-trimethylpsoralen. All of the isolated adducts have cis-syn stereochemistry. The stereochemistry and product distribution of the adducts are determined in part by the constraints imposed by the DNA helix on the geometry of the noncovalent intercalation complex formed by psoralen and DNA prior to irradiation.

Unreacted Methacrylate Groups on the Surfaces of Composite Resins

Abstract: The unreacted methacrylate groups on the surface of conventional composites and microfilled composites were studied by means of multiple internal reflection infrared spectroscopy. The influences of polymerization time, temperature, and the effect of polishing were studied. We also attempted to relate the results of some mechanical tests to the degree of chemical unsaturation measured in the different resins. All surface treatment and manipulative variables caused a decrease in double bond content and interfacial bond strength.

Picolinyl esters as derivatives for the structural determination of long chain branched and unsaturated fatty acids

Abstract: 3-Picolinyl esters were prepared from n-, iso-, anteiso- and unsaturated long chain fatty acids and were examined by gas chromatography and mass spectrometry The spectra contained ions which were diagnostic of the position of both the methyl branching and the double bond, and could be rationalized by assuming hydrogen abstraction from the chain by the nitrogen of the pyridine ring and cleavage at the resulting radical site The derivatives were easy to prepare and gave more informative spectra than the previously used pyrrolidides

Reaction of nitrogen dioxide with alkenes and polyunsaturated fatty acids: addition and hydrogen-abstraction mechanisms

Abstract: The reactions of nitrogen dioxide in a carrier gas (nitrogen, oxygen, or air) with cyclohexene and a series of mono-, di-, and trienes is reported at NO/sub 2/ concentrations ranging from 70 ppM to 50%. A complete product analysis was made with cyclohexene, and these data allow the calculation of the fraction of the NO/sub 2/ that reacts by addition to the double bond or by abstraction of an allylic hydrogen. At high concentrations of NO/sub 2/, addition is the predominant process, in agreement with the literature. However, below 10,000 ppM (1%), hydrogen abstraction predominates. It is suggested this is because of competition between a reversible addition and an irreversible H-abstraction step, much as is the case for the well-known bromine atom reaction system. In fact, a kinetic analysis shows that the ratios of rate constants for addition and abstraction are similar for both NO/sub 2/ and the bromine atom. A less direct method (analysis of water formed) was used to estimate the addition to abstraction ratio for other alkenes and for esters of unsaturated fatty acids; these data are in agreement with the cyclohexene data. The autoxidation of unsaturated fatty acid esters initiated by NO/sub 2/ also was studied,more » and kinetic chain lengths and autoxidizability ratios are given.« less

On the double bond isostere of the peptide bond: preparation of an enkephalin analogue

Abstract: Methodology for preparing dipeptide analogues in which a carbon-carbon double bond replaces the normal amide bond is described. Thus, the protected tyrosylglycine analogue, (S)-trans-5-t-butyloxycarbonylamino-6-(4-tbutoxyphenyl)hex-3-enoic acid has been synthesised and incorporated into the Leu-enkephalin analogue (3) by condensation with glycylphenylalanyl-leucine. The enkephalin analogue retained biological activity. The significance of this isosteric replacement of the amide group is discussed.

The rotational spectrum and molecular structure of the ethylene–HF complex

Abstract: The microwave spectrum of the ethylene–HF complex in the ground vibrational state has been assigned using a Fourier transform microwave spectrometer, employing a Fabry–Perot cavity and a pulsed supersonic nozzle as a molecular source. Ethylene–HF is nonplanar, with the axis of the HF subunit oriented perpendicular to the plane of the ethylene molecule, and bisecting the carbon–carbon double bond. A hydrogen bond is formed between the HF proton and the π‐electron density of ethylene. The spectroscopic constants of ethylene–HF and ethylene–DF are:

Estimates for systematic empirical corrections of consistent 4–21G ab initio geometries and their correlations to total energy group increments

Abstract: The structural parameters of the completely relaxed 4–21G ab initio geometries of more than 30 basic organic compounds are compared to experimental results. Some ranges for systematic empirical corrections, which relate 4–21G bond distances to experimental parameters, are associated with total energy increments. In general, for the currently feasible comparisons, the following corrections can be given which relate calculated distances to experimental r g parameters and calculated angles to r s -structures For CC single bond distances, deviations between calculated and observed parameters ( r g ) are in the ranges of −0.006(2) to −0.010(2) A for normal or unstrained hydrocarbons; −0.011(3) to −0.016(3) A for cyclobutane type compounds; and +0.001(5) to +0.004(4) A for CH 3 conjugated with CO. For CO single bonds the ranges are −0.006(9) to +0.002(3) A for CO conjugated with CO; and −0.019(3) to −0.027(9) A for aliphatic and ether compounds. A very large and exceptional discrepancy exists for the highly strained ethylene oxide, r s — r e = −0.049(5) A and in CH 3 OCH 3 and C 2 H 5 OCH 3 the r s — r e differences are −0.029(5), −0.040(10) and −0.025(10) A. Some of these discrepancies may also be due to deficiencies of the microwave substitution method caused by atomic coordinates close to inertial planes. For CN bonds, two types of NCH 3 corrections are from +0.005(6) to −0.006(6) and from −0.009(2) to −0.014(6) A; and the range for NCO is +0.012(3) to +0.028(4) A. For isolated CC double bonds the range is + 0.025(2) to +0.028(2) A. For conjugated CC double bonds the correction is less positive (+0.014(1) A for benzene). For CO double bonds the corrections are −0.004(3) to +0.003(3) A. For bond angles of type HCH, CCH, CCC, CCO, CCO, OCO, NCO and CCC the corrections are of the order of magnitude about 1–2° (or better). Angles centered at heteroatoms are less accurate than that, when hydrogen atoms are involved. Differences in HOC and NHC angles were found in a range of −2.3(5)° to −6.2(4)°.

A product study of the nitroxide inhibited thermal polymerization of styrene

Abstract: The efficient free radical scavengers 1,1,3,3-tetramethylisoindolinyl 2-oxy and 2,2,6,6-tetramethylpiperidinyl-1-oxy (nitroxides) disappear in styrene at 100°C with near zero order kinetics but at rates which are some 20 times higher than the known rate of initiation of thermal polymerization in the absence of scavenger A quantitative product analysis has shown that these inhibitors react by hydrogen abstraction from a thermally generated styrene dimer (1-phenyl-1,2,3,9-tetrahydronaphthalene) and to a minor extent by addition to the double bond of styrene monomer

Novel pi systems possessing cyclopropenylidene moiety

Abstract: As one of the most attractive Tr systems cyclopropenylidene metal complexes are prepared and their structure, especially carbene carbon—metal bonding is examined. In the lithium complex, this bonding is substantially ionic, on the other hand, in the transition metal complexes the carbene carbon—metal bond is shown to have double bond character by the ii back donation. The G donating and v accepting powers of cyclopropenylidenes change dramatically with presence or absence of amino substituent. Novel triafulvenes, triafulvalenes and related v system are taken up. The simplest triafulvenes and triafulvenes possessing conjugate Tr systems are synthesized. Triafulvalenes (3—5, 3—7, 3—9 systems) are also prepared. The structural features of these triafulvenes and triafulvalenes are discussed based on the spectral data. The parent compound of "cyclic dicalicene" which have peripheral l6v and central 8v structures is synthesized. The X ray analysis indicates that this novel system has planar (D2h) structure. Its v electron configuration is determined by i-H— and 1-3C—NMR spectra and MINDO/3 investigation.

Process for hydrogenating conjugated diene polymers

Abstract: A process for catalytically hydrogenating a carbon-carbon double bond of a conjugated diene polymer by introducing hydrogen in the solution of said polymer, characterized in that a palladium salt of a carboxylic acid is used as a catalyst.

cis‐trans isomerization of unsaturated fatty acids withp‐toluenesulfinic acid

Abstract: Elaidination of unsaturated fatty acids usingp-toluenesulfinic acid yielded 77–80% totaltrans unsaturation in the products. Results from reactions with monoene, diene, and triene isomers indicated that only geometric isomerization takes place. Each double bond isomerized randomly and independently in the polyunsaturated fatty acids. Reactions proceeded quickly, and the method proved convenient and reliable.

Photoinitiators and photoinitiation, 3. Comparison of the photodecompositions of α‐methoxy‐ and α,α‐dimethoxydeoxybenzoin in 1,1‐diphenylethylene as model substrate

Abstract: The photodecomposition of α-methoxydeoxybenzoin (1) and α,α-dimethoxydeoxybenzoin (2) was investigated both in the absence and in the presence of 1,1-diphenylethylene. The resulting products indicate that benzoyl radicals add to the olefinic double bond (initiation of polymerization), whereas the α-methoxybenzyl radicals generated from 1 do not add to the olefinic double bond (no initiation), but preferentially combine with other radicals (termination of polymerization). This reaction is largely suppressed in the case of α,α-dimethoxybenzyl radicals generated from 2 owing to sequential fragmentation into inactive methylbenzoate and highly reactive methyl radicals which add to the olefinic double bond and thus contribute to the initiation.

A spectroscopic study of proton transfer and photochromism in N-(2-hydroxybenzylidene)aniline

Abstract: The infrared spectral characteristics of N-(2-hydroxybenzylidene)aniline, its deuterium substituted analogue, N-(2-hydroxybenzylidene)-m-toluidine, and their photoproducts have been investigated. The infrared spectrum of a low temperature polycrystalline film of N-(2-hydroxybenzylidene)aniline exhibits new absorption bands at 3380, 1646, 1537, 1502, 1319, and 1310 cm−1 upon irradiation at 365 nm. Likewise, the spectrum of the m-toluidine derivative exhibits new absorption bands at 3320, 1650, 1535, 1503, 1321, 1310, and 995 cm−1 upon irradiation at 365 nm. These new data, in conjunction with the newly acquired data on the hydrochloride and deuterochloride of the title compound, indicate that the photoproduct is a zwitterion, not an ortho-quinone. It is also inferrred that the photoproduct exists in a conformation which is cis about the central carbon–nitrogen double bond.

Antithrombogenic biomedical material

Abstract: Provided is an antithrombogenic biomedical material comprising a copolymer of (A) not less than 5% by weight of one or more polymerizable monomers having a polyethylene oxide unit with a degree of polymerization not less than 5 and a polymerizable carbon-carbon double bond and (B) not more than 95% by weight of one or more monomers copolymerizable with said monomer (A).

Synthesis of polyethylene oxide macromers

Abstract: Anionic “living” polymerization of oxirane was shown to be efficient for the synthesis of polyethylene oxide macromers. The double bond at chainend was introduced either upon initiation or upon deactivation. The macromers obtained were characterized carefully to establish quantitatively the presence of the end-standing double bond. The species are well defined and of narrow molecular weight distribution.