Showing papers on "Double bond published in 1987"

Ferroelectric liquid crystals

Abstract: Ferroelectric liquid crystal mixture containing at least one compound of the general formula … … where n is 0 or 1, X is a single covalent bond, -COO- or -OOC-, X is a single covalent bond, -COO-, -OOC-, -CH2CH2-, -OCH2- or -CH2O-, the rings A , A and A are each independently of the others unsubstituted or cyano-, halogen- or lower alkyl-substituted 1,4-phenylene or one of the rings may also be pyrimidine-2,5-diyl or pyrazine-2,5-diyl and/or when n is 1 one of the rings may also be trans-1,4-cyclohexylene or trans-m-dioxane-2,5-diyl, with the proviso that one of the rings present is pyrimidine-2,5-diyl or pyrazine-2,5-diyl if a further ring is trans-1,4-cyclohexylene or, if n is 0 and X is a single covalent bond, R and R are each as defined in Claim 1, at least R having a C-C double bond,… and novel compounds of the formula I.

Barriers to rotation adjacent to double bonds. 3. The carbon-oxygen barrier in formic acid, methyl formate, acetic acid, and methyl acetate. The origin of ester and amide resonance

Abstract: The structures of the rotamers about the C-O bonds of formic acid, methyl formate, acetic acid, and methyl acetate were calculated by using the 6-31G* basis set and complete geometrical relaxation Large basis sets (6-311+G**) and correction for electron correlation were needed in order to obtain calculated barriers that were in good agreement with the available experimental data The factors that control the geometry at a carbonyl group are considered, and it is shown that an analysis in terms of bond path angles leads to a direct connection with electronegativity The nature of the interaction between an amino group and a carbonyl, as in an amide, is examined and shown not to involve charge transfer from the nitrogen to the carbonyl oxygen, but rather it involves charge transfer between carbon and nitrogen The origin of the rotational barrier in esters and of the difference in energy between the E and Z conformers is discussed

Chemistry of the Silicon-Silicon Double Bond

Abstract: Disilenes, compounds containing silicon-silicon double bonds, can be isolated as thermally stable, yellow- or orange-colored crystalline compounds; the substituent groups at silicon must be large (mesityl, tert -butyl, etc.) to prevent polymerization. Structural and spectro-scopic studies indicate many similarities between the 3p–3p π bonding in disilenes and the 2p-2p π bonding in olefins, but disilenes are much more reactive than alkenes. The reactions of disilenes lead to many new classes of silicon compounds, including three- and four-membered rings which present novel problems in chemical bonding.

Mechanistic studies on the cobalt(II) Schiff base catalyzed oxidation of olefins by O2

Abstract: The cobalt complex (bis(salicylidene-..gamma..-iminopropyl)methylamine)cobalt(II), CoSMDPT, has been shown to catalytically oxidize olefins in the presence of dioxygen or hydrogen peroxide. When terminal olefins are oxidized, the methyl ketone and corresponding secondary alcohol are produced selectively. Internal as well as terminal olefins are oxidized. The most common pathway for the oxidation of olefins catalyzed by first-row transition metals-autoxidation-has been ruled out in this system. A Wacker-type mechanism, oxidation by peracids, and mechanisms involving the formation of peroxymetallocycles have also been ruled out. A new mechanism for O/sub 2/ oxidations is proposed which involves oxidation of the primary alcohol solvent by CoSMDPT to produce the corresponding aldehyde and hydrogen peroxide. Reaction of hydrogen peroxide with CoSMDPT occurs to form a cobalt hydroperoxide, which can be viewed as a stabilized hydroperoxy radical which has spin paired with the d/sub z/sup 2// electron of CoSMDPT. The cobalt hydroperoxide then adds to the olefin double bond, leading to formation of an alkyl hydroperoxide. Haber-Weiss decomposition of this alkyl hydroperoxide by CoSMDPT produces the observed ketone and alcohol products. Deactivation of the catalyst is due to oxidation of the ligand system of the cobalt complex as well as formation of a ..mu..-peroxo-dicobalt complex.

Unsaturated Molecules Containing Main Group Metals

Abstract: Molecules in which there are neighboring electrophilic and nucleophilic centers are unusually reactive. Oligomerization can be prevented only by bulky groups attached to the main group metal atom that would act as electron pair acceptor, or to the basic non-metal atom. The basic and the acid centers behave as a single unit in chemical reactions; the system is similar to a “double bond” whose π-electron density is largely concentrated at one atom. The unsaturated nature of these molecules can be seen in (for example) their addition reactions with hydrogen compounds of non-metals, or in reactions that are distantly related to cycloadditions at homopolar double bonds. The selection of suitable reaction partners leads to polycyclic, cage-like molecules containing metal atoms. If these atoms possess lone pairs (as is usual in the lower oxidation states of the third and fourth main groups), these can be utilized to form bonds to further (Lewis acid) metal centers. In some cases large assemblies can be built up from polycyclic systems in this way; a characteristic of these assemblies is a one-dimensional array of metal atoms. Commonly occurring structural features of the polycyclic species are tetrahedra, trigonal bipyramids and cubes.

Preparation, characterization, and x-ray crystal structure of an acetonitrile-complexed ruthenium silylene

Abstract: Silylene complexes (L/sub n/M double bond SiR/sub 2/) are postulated intermediates in a number of transition-metal-mediated transformations, including Rochow's direct process, catalytic redistribution of silanes, and various silylene-transfer reactions. Unfortunately, such species have been synthetically elusive, despite the well-established existence of congeneric carbene, germylene, stannylene, and plumbylene complexes. Although numerous examples of silylene-bridged bimetallic species exist, there are no well-characterized examples of compounds possessing a formal metal-silicon double bond, despite numerous attempts to prepare them. To investigate the chemistry of transition-metal-silicon double bonds, the authors are attempting to develop synthetic routes to such terminal silylene complexes. Here the authors report the first synthesis and complete structural characterization of a base-stabilized transition-metal silylene complex.

Structure of Phosphorus Oxynitride Glasses

Abstract: The structures of phosphourus oxynitride glasses have been determined using a combination of solid-state 31P, 15N, and 23Na nuclear magnetic resonance and Raman spectroscopies. Raman spectra of model phosphazene compounds with different types of P–N bonding have been used to confirm spectral assignments. Results indicate that nitrogen replaces oxygen in the phosphrus atoms (via one double bond and one single bond) and as nitrogen bonded to three phosphorus atoms via three single bonds. The observed structural features are consistent with data which show that nitrogen influences the chemical durability, thermal expansion, and other properties of phosphate glasses by cross-linking ploymeric phosphate chain to gether in the glass network.

Mass spectra of the picolinyl esters of isomeric mono- and dienoic fatty acids.

Abstract: The picolinyl ester derivatives of the complete series of isomeric octadecenoates, methylene-interrupted octadecadienoates, and of octadec-9-ynoate have been subjected to gas chromatography-mass spectrometry. A fused-silica capillary column, coated with a cross-linked methyl silicone, was used for the separation. Electron impact spectra were determined at 70 eV. Earlier observations with a limited series of model compounds were confirmed, and it was shown that the picolinyl ester derivatives were of almost universal value in the location of double bonds in such isomers. Difficulties of interpretation arose mainly when the double bonds were close to the carboxyl group.

The first stable transition metal (molybdenum or tungsten) complexes having a metal–phosphorus(III) double bond: the phosphorus analogues of metal aryl- and alkyl-imides; X-ray structure of [Mo(η-C5H5)2(PAr)](Ar = C6H2But3-2,4,6)

Abstract: Arylphosphinylidenemetal complexes [M(η-C5H5)2(PAr)][M = Mo (1) or W (2), Ar = C6H2But3-2,4,6] and an alkyl analogue [W(η-C5H5)2(PR)][R = CH(SiMe3)2(3)] have been prepared from [{M(η-C5H5)2HLi}4] and PCl2R′(R′= Ar or R), and show low-field 31P chemical shifts: δ(31P{1H})(C6D6)(1)+ 799.5 [J(31P–1H) 4 Hz (involving only one of the two C5H5 rings)]; (2)+666.1 [J(31P–183W) 153.5 Hz, J(31P–1H) 4 Hz]; and (3)+679.6 [J(31P–183W) 144.1 Hz]. Compound (1) has an Mo–P bond length of 2.370(2)A and a Mo–P–C bond angle of 115.8(2)°.

In Situ Generation and Synthetic Application of 2-Phenylbenzimidazoline to the Selective Reduction of Carbon–Carbon Double Bonds of Electron-Deficient Olefins

Abstract: 2-Phenylbenzimidazoline (PBI) as a mild, selective, and convenient reducing agent was efficiently generated in situ from o-phenylenediamine and benzaldehyde in alcohols. A generally applicable method for the selective reduction of carbon–carbon double bonds of a variety of electron-deficient olefins with an alcoholic solution of PBI is described. The reduction of α,β-unsaturated ketones to the corresponding saturated ketones could also be accomplished (but, less effectively) with PBI with the aid of a Lewis-acid catalyst. 1-Methyl-2-(o-nitrophenyl)benzimidazoline prepared and isolated by the reaction of o-nitrobenzaldehyde with N-methyl-o-phenylenediamine reduced benzylidenemalononitrile to give benzylmalononitrile and 1-methyl-2-(o-nitrophenyl)benzimidazole in high yields. This shows the validity of PBI to be the actual reducing species in the present reduction system. From a mechanistic study, the present reductions could be interpreted in terms of a mechanism involving a synchronous transport of a pair...

Surface areas of 1-palmitoyl phosphatidylcholines and their interactions with cholesterol.

Abstract: 1-Palmitoyl phosphatidylcholines (1-palmitoyl PCs), in which the 2-position was occupied respectively by C10:0, C12:0, C14:0, C14:1, n-7, C16:0, C16:1, n-7, C18:0, C18:1(t), n-9, C18:1, n-9, C18:2, n-6, C18:3, N-3, C18:3, n-6, C18:3(5t,9,12), C22:0, C22:1, n-9, C22:2, n-6, C22:3, n-3, C22:4, n-6, C22:5, n-6 or C22:6, n-3 fatty acids, were studied as monolayer films at the air/water interface. Results for molecular area indicated that the areas of the PC (phosphatidylcholine) did not continuously decrease as the length of one chain increased. For series of saturated, monoenoic and dienoic 1-palmitoyl PCs the smallest molecular area was occupied by the PC containing a 20-carbon acid at the 2-position. In the 18-carbon series, introduction of the first and third cis double bonds caused a large increase in molecular area, but in the 22-carbon series the first and second cis double bonds produced large increases in molecular area. Molecules containing three or more cis double bonds varied little in molecular area, regardless of chain length (18-22 carbon atoms). The influence of a trans double bond was intermediate between that of a saturated and a cis double bond. The 18- and 22-carbon series of PCs were studied in mixed monolayers with cholesterol and desmosterol. Condensation of molecular areas occurred in all sterol PC mixed films, and similar results were obtained with cholesterol and desmosterol. Condensation of PC containing a cis or trans double bond within 10 carbon atoms of the carboxy group initially increased with increasing surface pressure. Condensation of other PCs decreased as surface pressure increased. All cis- or trans-unsaturated PCs condensed maximally in mixtures of approximately equimolar ratios with sterols, but saturated PCs condensed to the greatest extent in mixtures that contained about 30 mol% sterol.

Structure of 2,3-butanedione dihydrazone and IR study of higher polyazines: a new class of polymeric conductors

Abstract: Polyazines, H/sub 2/N single bond (N double bond C(CH/sub 3/) single bond C(CH/sub 3/) double bond N)/sub x/ single bond NH/sub 2/, of various chain lengths have been prepared and studied by IR spectroscopy. An x-ray crystal structure was done on the monomer of this series, 2,3-butanedione dihydrazone (x = 1). It crystallized in space group P4/sub 2//n with cell constants a = 12.172 (3) A and c = 4.115 (1) A and Z = 4; intensity data were collected from 3.0/sup 0/ less than or equal to 2theta less than or equal to 65.0/sup 0/. The monomer is planar with long carbon nitrogen double bonds (1.291 (1) A) in the E conformation, the methyl groups are anti across the short carbon-carbon single bond (1.474 (2) A), and the lone pairs across the nitrogen-nitrogen single bonds are gauche. The anomalous bond lengths indicate a degree of ..pi..-bond conjugation in this molecule. The higher molecular weight materials are yellow to brown powders, are stable to air, have high melting points, and are surprisingly resistant to hydrolysis. Correlation of IR spectra of the monomer and sequentially increasing chain length polymers shows that the highest molecular weight material is at least 45 monomermore » units long and is planar with double bonds in the E conformation and all single bonds in the anti conformation. As in the monomer, the position of the C double bond N resonance indicates conjugation of the ..pi.. system along with polymer chain.« less

Metal d.pi.-ligand .pi. conflicts in octahedral oxo, carbyne, and carbonyl complexes

Abstract: Metal-ligand ..pi.. interactions in group VI model compounds containing oxo, carbyne, and carbonyl ligands are probed with use of the extended Hueckel method. The interplay between M double bond O ..pi.. bonding optimization and the metal sigma framework geometry in (MoO/sub 2/H/sub 4/)/sup 2 -/ is examined first. The importance of oxygen's electronegativity for housing lone pairs in monomers containing terminal oxygens is noted and later contrasted with similar model compounds containing carbyne ligands. Calculations on (W(CH)/sub 2/H/sub 4/)/sup 4 -/ confirm the qualitative expectation that a nonbonding carbon 2p orbital combination exists for both cis and trans isomers. Even though this orbital is not at particularly high energy for a filled frontier orbital, they anticipate that these carbyne carbons will be vary nucleophilic if filled or very electrophilic if vacant; i.e., they will resemble a carbanion or a carbonium ion. A mixed oxocarbyne complex, such as (W(CH)(O)H/sub 4/)/sup 3 -/ will exhibit a d..pi.. conflict with the covalency requirements of the carbyne causing electron density to build up on the terminal oxygen. Competition for d..pi.. orbitals also results when ..pi..-acid ligands are trans to ..pi..-donor ligands. Recognition of ..pi..-acid/..pi..-donor d..pi.. conflicts rationalizes the cis geometry of W(O)(CO) in d/supmore » 2/ M(O)(CO)L/sub 4/ octahedra.« less

Sulfuration of the norbornene double bond

Abstract: Sulfuration par S 8 des norbornene, dicyclopentadiene, isodicyclopentadiene, norbornadiene, dihydro-1,4 methano-1,4naphtalene, aryl-2 norbornenes et sesquinorbornene: obtention dans la plupart des cas de trithiolannes-1,2,3 eventuellement avec des pentathiepannes-1,2,3,4,5. Mecanismes

Photopolymerizable composition and photopolymerizable recording material containing same

Abstract: Upon imagewise exposure, a photopolymerizable composition which contains (a) a polymeric binder; (b) a compound that has at least one terminal ethylenic double bond and a boiling temperature, at standard pressure, of above 100° C., and that can form a polymer by polymerization initiated by a free-radical process; (c) a photoinitiator; (d) a leuco base of a triarylmethane dye; and (e) a photochromic spiro-indolino-benzopyran compound represented by the formula ##STR1## wherein R denotes a hydrogen atom or a C1 -to-C16 alkyl group, R1, R2, R3 and R4 are identical or different, and each denotes a hydrogen or a halogen atom, a C1 -to-C4 alkyl or alkoxy group, or a nitro group, and R5, R6, R7 and R8 are identical or different, and each denotes a hydrogen or a halogen atom, a nitro or an amino group, a C1 -to-C5 alkyl or alkoxy group, or a C6 -to-C10 aryl group exhibits a strong color contrast which is maintained even after prolonged storage.