Search results for "Butadiene"
showing 10 items of 106 documents
1,4-regioselective iodofunctionalizations of 1,3-butadiene
1988
Abstract Addition reactions of benzene and acetonitrile to 1,3-butadiene are described. This new iodofunctionalization process proceeds “via” iodonium ion-allylic cation equilibrium and gives regioselectively 1,4-adducts, which can be alternatively obtained by acid treatment of the 1,2-derivative 8 .
Comparative chemistry of 18-electron Mo(II) and 17-electron Mo(III) compounds containing only carbon-based ligands
1998
International audience; The chemical reactivity of various kinetically stable isomers of compound CpMo(η3-C3H5)(η4-C4H6), 1, and its oxidation product [1]+, as well as the bis-allyl Mo(III) complex CpMo(η3-C3H5)2, 2, and the bis-diene Mo(II) complex [CpMo(η4-C4H6)2]+, 3, is reviewed. The inertness toward isomerization processes of the allyl and butadiene ligands in the Mo(II) complexes has allowed a study of the relative reactivity toward both electrophilic and nucleophilic addition processes as a function of coordination mode. The dependence of various reaction pathways on the metal oxidation state has also been investigated. Of particular interest is the discovery that the electronically …
Theoretical study of the low‐lying states of trans‐1,3‐butadiene
1992
We present extensive ab initio calculations on the low‐lying electronic states of trans‐1,3‐butadiene within the multireference configuration interaction (MRCI) framework by selecting the configurations with a perturbative criterion. The X 1Ag ground state and 1 3Bu, 1 3Ag, 2 1Ag, and 1 1Bu valence excited states have been calculated at a fixed geometry. The results obtained are in good agreement with previous experimental and calculated values, and could help to understand polyene spectroscopy, photochemistry, and photophysics. The advantages of a MRCI method where the most important contributions to the total MRCI wave function, perturbatively selected, are treated variationally, and the …
1,3-Dipolar cycloaddition of diaryldiazomethanes across N-ethoxy-carbonyl-N-(2,2,2-trichloroethylidene)amine and reactivity of the resulting 2-azabut…
2016
Abstract 1,3-dipolar cycloaddition of diaryldiazomethanes Ar2C N2 across Cl3C–CH N–CO2Et 1 yields Δ3-1,2,4-triazolines 2. Thermolysis of 2 leads, via transient azomethine ylides 3, to diaryldichloroazabutadienes [Ar(Ar')C N–CH CCl2] 4. Treatment of 4a (Ar = Ar' = C6H5) and 4c (Ar = Ar' = p-ClC6H4) with NaSR in DMF yields 2-azabutadienes [Ar2C N–C(H) C(SR)2] 5. In contrast, nucleophilic attack of NaStBu on 4 affords azadienic dithioethers [Ar2C N–C(StBu) C(H)(StBu)] (7a Ar = C6H5; 7b Ar' = p-ClC6H4). The reaction of 4a with NaSEt conducted in neat EtSH produces [Ph2C N–C(H)(SEt)–CCl2H] 8, which after dehydrochloration by NaOMe and subsequent addition of NaSEt is converted to [Ph2C N–C(SEt) C…
Cd(II) and Cu(II) coordination polymers constructed from the expanded 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene ligand: conventional and ultrasound-…
2018
Shaabani, Behrouz/0000-0001-5576-4604; Kubicki, Maciej/0000-0001-7202-9169; Grzeskiewicz, Anita M./0000-0003-0377-2260 WOS: 000447971700041 A 3D open inorganic/organic framework, {[Cd(mu-L)(mu(3)-SO4)(H2O)]center dot H2O}(n) (1) [L = 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene] was synthesized by the reaction of CdSO4 center dot 8H(2)O with L. The treatment of Cu(NO3)(2)center dot 3H(2)O with the same N,N'-donor ligand in two different solvent mixtures, methanol/ dichloromethane (2) and methanol/ chloroform (3), afforded two new ladder-like coordination polymers of formula {[Cu(mu-L)(mu-NO3)(NO3)]center dot solv}(n) [solv = CH2Cl2 (2) and CHCl3 (3)]. The non-interpenetrated ladder motifs 2 a…
Chlamydomonas reinhardtii in the landscape of pigments.
2004
▪ Abstract This review focuses on the biosynthesis of pigments in the unicellular alga Chlamydomonas reinhardtii and their physiological and regulatory functions in the context of information gathered from studies of other photosynthetic organisms. C. reinhardtii is serving as an important model organism for studies of photosynthesis and the pigments associated with the photosynthetic apparatus. Despite extensive information pertaining to the biosynthetic pathways critical for making chlorophylls and carotenoids, we are just beginning to understand the control of these pathways, the coordination between pigment and apoprotein synthesis, and the interactions between the activities of these…
Liquid/Gas and Liquid/Liquid Phase Behavior of n-Butane/1,4-Polybutadiene versus n-Butane/1,2-Polybutadiene
2005
Solutions of 1,4-polybutadiene (1,4-PB, 98% cis) and of 1,2-polybutadiene (1,2-PB) in n-butane (n-C 4 ) were studied with respect to their vapor pressure and to their demixing into two liquid phases under isochoric conditions within the temperature range from 25 to 75 °C. 1,2-PB mixes homogeneously with n-C 4 at any ratio, in contrast to 1,4-PB, which exhibits a miscibility gap extending from practically pure solvent to approximately 40 wt % polymer. Corresponding to these solubility differences, the vapor pressures for the system n-C 4 /1,4-PB are considerably higher than for n-C 4 /1,2-PB at the same concentration and temperature. The experimental results are modeled accurately and consis…
Reptation and constraint release
1991
Abstract The reptation and constraint release models are discussed by considering three recent experimental examples: (1) the diffusion of hydrogenated polybutadiene in matrices of molecular weights raning between 1 ⩽ Mw / Me ⩽ 253; (2) the diffusion of polystyrene (PS) chains in matrices of star branched PS; (3) the diffusion of very long PS chains in chemically cross-linked PS-networks. It is concluded that the reptation and constraint release models are applicable, but ‘constraint release’ should be understood in a wider sense allowing for non-reptative removal of barriers to lateral chain motion. The analysis of the third example proves that lateral modes of motion have a negligible inf…
Intramolecular caging in polybutadiene due to rotational barriers
2003
We present molecular dynamics simulations of a chemically realistic model of 1,4-polybutadiene and a freely rotating chain model derived from the first model by neglecting all dihedral potentials. We show that the presence of energy barriers hindering dihedral rotation leads to an intermediate plateau regime in the tagged particle mean-squared displacement reminiscent of the cage effect underlying the mode-coupling description of the liquid-glass transition. This intramolecular caging, however, occurs already at temperatures well above the glass transition regime. Because of its different physical origin, it also does not comply with the theoretical predictions of the mode-coupling theory. …
The molecular dynamics of thermoreversible networks as studied by broadband dielectric spectroscopy
1995
Polybutadienes modified by a small number of 4-phenyl-1,2,4-triazoline-3,5-dione form thermoreversible networks via hydrogen bonding between the polar stickers. The molecular dynamics of systems with different contents of polar stickers are investigated by broadband dielectric spectroscopy in the frequency regime of 10−1–109 Hz. Unmodified polybutadiene shows two relaxation processes, the α-relaxation which is correlated to the dynamic glass transition of the polybutadiene, and a β-relaxation corresponding to a local relaxation of polybutadiene segments. In the polar functionalized systems, besides these two relaxations, an additional relaxation process (called α*) is observed, which occurs…