Double bond

About: Double bond is a research topic. Over the lifetime, 29147 publications have been published within this topic receiving 425077 citations.

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.

Chemical Bonding in Higher Main Group Elements

Abstract: Many concepts used for a qualitative description of chemical bonding that originated in the early days of theoretical chemistry have been vindicated recently by quantum chemical calculations, at least as far as first row elements are concerned. However, many concepts that have been justified for first row elements (Li to Ne) cannot—contrary to widespread belief—be generalized to the higher main group elements. This applies particularly to the concept of hybridization, which should be viewed with considerable caution. The essential difference between the atoms of the first and higher rows is that the cores of the former contain only s-AOs, whereas the cores of the latter include at least s- and p-AOs. As a consequence, the s and p valence AOs of first row atoms are localized in roughly the same region of space, while the p valence AOs of higher row atoms are much more extended in space. This has the consequence that for the light main group elements both lone-pair repulsion and isovalent hybridization play a greater role than for the heavy main group elements. Furthermore, this implies that single bonds between first row elements are weak and multiple bonds are strong, whereas for the second or higher row elements single bonds are strong and multiple bonds weak. The “extended valence” (violation of the octet rule) observed in compounds of higher main group elements has very little to do with the availability of d-AOs but is due rather to the size of these atoms and thus to the reduced steric hindrance between ligands and, to a lesser extent, also to the lower electronegativity of the heavy atoms. A model based on the concept of electron-rich multicenter bonds is certainly closer to reality than one involving hybrids with the participation of d-AOs. The XO bonds in phosphane oxides, sulfoxides, oxo acids and related compounds are better formulated as semipolar rather than as true double bonds, even if they behave in some respects like double bonds.—The growing interest of theorists in compounds of higher main group elements parallels new and, in some instances, spectacular results of experimental research on the chemistry of these elements.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Abstract: Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C–C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C–C bond cleavage, and C–H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C–C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven...

Tetramesityldisilene, a stable compound containing a silicon-silicon double bond

Abstract: Irradiation of 2,2-bis(2,4,6-trimethylphenyl)hexamethyltrisilane in hydrocarbon solution produces tetramesityldisilene, which can be isolated as a yellow-orange solid stable to room temperature and above in the absence of air Like the olefins of carbon chemistry, tetramesityldisilene undergoes addition reactions across the silicon-silicon double bond

Red-, blue-, or no-shift in hydrogen bonds: a unified explanation.

Abstract: We provide a simple explanation for X-H bond contraction and the associated blue shift and decrease of intensity in IR spectrum of the so-called improper hydrogen bonds This explanation organizes hydrogen bonds (HBs) with a seemingly random relationship between the X-H bond length (and IR frequency and its intensity) to its interaction energy The factors which affect the X-H bond in all X-H [midline ellipsis] Y HBs can be divided into two parts: (a) The electron affinity of X causes a net gain of electron density at the X-H bond region in the presence of Y and encourages an X-H bond contraction (b) The well understood attractive interaction between the positive H and electron rich Y forces an X-H bond elongation For electron rich, highly polar X-H bonds (proper HB donors) the latter almost always dominates and results in X-H bond elongation, whereas for less polar, electron poor X-H bonds (pro-improper HB donors) the effect of the former is noticeable if Y is not a very strong HB acceptor Although both the above factors increase with increasing HB acceptor ability of Y, the shortening effect dominates over a range of Ys for suitable pro-improper X-Hs resulting in a surprising trend of decreasing X-H bond length with increasing HB acceptor ability The observed frequency and intensity variations follow naturally The possibility of HBs which do not show any IR frequency change in the X-H stretching mode also directly follows from this explanation