Resonance Raman spectroscopy of butadiene: Demonstration of a 2 1Ag state below the 1 1Bu V state

Resonance Raman spectra of butadiene obtained with radiation in the 230-218 nm range exhibit activity in combinations and overtones of a mode of b_u symmetry. The pattern of the observed bands must be due to vibronic activity of this mode in a state of A_g symmetry. We conclude that the 2 ¹A_g state of butadiene lies between 5.4 and 5.8 eV, below the 1 ¹B_u state at 5.8 to 6.3 eV.     

Atom Transfer Radical Polymerization of Butadiene Initiated by Benzyl Chloride/MoCl5 Substituted by 1-octanol/PPh3

A novel initiator system, benzyl chloride/MoCl₅ substituted by 1-octanol/triphenyl phosphine (PPh₃), was applied to the atom transfer radical polymerization (ATRP) of butadiene. The characterization revealed the linear increase of the number average molecular weight with the monomer conversion and the rather wide molecular weight distributions of the polymerization products. The microstructure of the butadiene was detected by IR and ¹H-NMR. The chlorine atom at ω –end group of the polymer and the change of valence states of molybdenum detected by UV–Vis spectra revealed that the polymerization accorded primarily with the mechanism of ATRP.     

Polymerization and copolymerization of 2-phthalimidomethyl 1,3-butadiene. I. Preliminary studies of free radical polymerization and polymerizations initiated by various transition metal allyl complexes

2-Phthalimidomethyl 1,3-butadiene was homopolymerized and copolymerized with butadiene by free radical initiators; r₁ and r₂ were close to 1. All the attempts to polymerize 2PMB anionically have been unsuccessful. Preliminary studies of various η³-allylic catalysts showed that η³-allyl M₀(CO)₃OOCCF₃ initiates the polymerization of butadiene and is not sensitive to N-methyl phthalimide (NMP); neither does it initiate the copolymerization of butadiene and 2PMB. On the other hand, a catalyst that results from the reaction of allyl trifluoroacetate with nickel tetracarbonyl is efficient for the copolymerization of butadiene and 2PMB. η³-Allyl nickel trifluoroacetate was prepared in heptane or benzene and used in benzene or methylene chloride. In all cases it initiated the copolymerization of butadiene with 2PMB     

MoO_2Br_2体系催化丁二烯聚合中烯丙基卤素的作用

ＭｏＯ２Ｂｒ２－Ａｌ（ｉ－Ｂｕ）２ＯＰｈＣＨ３（－ｍ）体系催化丁二烯１，２－聚合过程中添加Ｃ３Ｈ５Ｘ（Ｘ＝Ｃｌ、Ｂｒ和Ｉ）对聚合物分子量有较好的调节作用，其中以Ｃ３Ｈ５Ｂｒ的调节作用最强，Ｍｎ从１７．５×１０５降至３．５×１０５，但对催化活性有一定的影响．在测定催化体系的ＵＶ光谱、（１３）Ｃ－ＮＭＲ谱、聚合活性和聚合动力学参数的基础上，讨论了Ｃ３Ｈ５Ｘ在催化体系中的行为．     

(Cyclopentadienyl)(1-methylallyl)(butadiene)titanium

(Cyclopentadienyl)(1-methylallyl)(butadiene)titanium, C₁₃H₁₈Ti, has been obtained from the reaction between (C₅H₅)TiCl₃ or (C₅H₅)TiCl₂ and 1-methylallylmagnesium bromide in ether. The brown compound is diamagnetic and thermally stable, but very sensitive to oxygen. The nature of the new compound has been elucidated from its reaction with bromine and by IR, ¹H and ¹³C NMR, and mass spectral analysis.     

Quantum-chemical simulation of unit process for the oxidation reactions of ethylene and its derivatives invoving <Superscript>1</Superscript>O<Subscript>2</Subscript> (<Superscript>1</Superscript>Δg)

The results of simulation of oxidation reactions of ethylene derivatives with different substituents (F atoms, CH₃O and CH₃ groups) and butadiene molecule with participation of ¹O₂ (¹Δg) have shown the possibility to realize different routes for the majority of the considered reactions. The largest product variety is obtained for butadiene and CH₃ derivatives of ethylene. For butadiene, along with 1,2-cycloaddition reactions resulting in four-membered dioxetane (which is realized in all cases), the possibility to form six-membered cyclic epidioxides (1,4-addition) and diepoxide products with two three-membered rings (epoxidation) has been found. The formation of hydroperoxide forms along with 1,2-addition reactions is also possible for all CH₃ derivatives of ethylene. Formation conditions and relative stability of the noted products have been analyzed for each case and certain features of the revealed reaction pathways with the transfer of two oxygen atoms have been discussed.     

Styrene/1,3‐butadiene copolymerization by C2‐symmetric group 4 metallocenes based catalysts

C₂‐symmetric group 4 metallocenes based catalysts (rac‐[CH₂(3‐tert‐butyl‐1‐indenyl)₂]ZrCl₂ (1) , rac‐[CH₂(1‐indenyl)₂]ZrCl₂ (2) and rac‐[CH₂(3‐tert‐butyl‐1‐indenyl)₂]TiCl₂ (3) ) are able to copolymerize styrene and 1,3‐butadiene, to give products with high molecular weight. In agreement with symmetry properties of metallocene precatalysts, styrene homosequences are in isotactic arrangements. Full determination of microstructure of copolymers was obtained by ¹³C NMR and FTIR analysis and it reveals that insertion of butadiene on styrene chain‐end happens prevailingly with 1,4‐trans configuration. In the butadiene homosequences, using zirconocene‐based catalysts, the 1,4‐trans arrangement is favored over 1,4‐cis, but the latter is prevailing in the presence of titanocene (3) . Diad composition analysis of the copolymers makes possible to estimate the reactivity ratios of copolymerization: zirconocenes (1) and (2) produced copolymers having r₁ × r₂ = 0.5 and 3.0, respectively (where 1 refers to styrene and 2 to butadiene); while titanocene (3) gave tendencially blocky styrene–butadiene copolymers (r₁ × r₂ = 8.5). The copolymers do not exhibit crystallinity, even when they contain a high molar fraction of styrene. Probably, comonomer homosequences are too short to crystallize (n_s = 16, in the copolymer at highest styrene molar fraction). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1476–1487, 2008     

Copolymerization of 1,3-butadiene and styrene with a neodymium catalyst

Homo- and copolymerization of butadiene and styrene in the presence of the catalyst system Nd(octanoate)₃/CCl₄/Al(iBu)₃ (iBu: isobutyl) were investigated at 60°C in heptane as solvent. The initiating catalyst system is very effective in the polymerization of butadiene. However, the presented copolymerization of butadiene and styrene is only practicable when using a special addition order of the catalyst components and a prescribed ageing phase. Copolymers obtained from various monomer feed ratios were characterized by ¹H and ¹³C NMR spectroscopy and gel-permeation chromatography (GPC). The copolymer characteristics especially microstructure, molar mass and molar-mass distribution (MMD) are strongly dependent on the composition of the monomer mixture.     

All-valence-electron CI treatment of the electronic spectrum of trans-butadiene

An all-valence-electron CI treatment is reported for the low-lying valence and Rydberg states of butadiene. All singly- and doubly-excited configurations relative to a series of the leading terms in a given CI expansion are taken into account, with resulting secular equation orders of as high as 150 000. The agreement between calculated and experimental transition energies is invariably better than 0.2 eV where comparison is possible, with all low-lying valence triplet and Rydberg singlet excited states being unambiguously assigned. The valence-shell excitation to the 2 ¹A_g species is concluded to correspond to the 7.06 eV band system, while the forbidden singlet—singlet transition reported by McDiarmid is assigned as x₂ → 3s. The possibility of an avoided crossing between Rydberg valence ¹B_u excited states having a determining influence on the appearance of the broad intense V₁—N absorption is also discussed.     

Second virial coefficients of homopolymers and copolymers of butadiene and styrene in tetrahydrofuran

Second virial coefficients have been measured in tetrahydrofuran for a series of anionically polymerized narrow distribution homopolymers and copolymers of butadiene and styrene. The results fit the general empirical equation A₂ = M^?1/4(0.0216w_B + 0.00995w_S + Cw_Bw_S), where M is the polymer molecular weight, w_B and w_s are the weight fractions of butadiene and styrene, and C is a constant which is zero for block polymers and equal to 7.9 × 10^—3 for random copolymers. The equation is independent of the degree of 1,2 addition of butadiene and fits data on both linear and tetrachain star-branched polymers within experimental error.     

Ethene-butadiene copolymers by single-site catalysts

Constrained geometry catalysts ([Me₂Si(N^tBu)(Me₄Cp)]TiCl₂) were used to copolymerize ethene and 1,3-butadiene. It is possible to incorporate 17 mol% of butadiene, other catalyst systems such as CpTiCl₃/MAO show much lower incorporation. More than 300 000 kg of copolymer can be obtained by one mol of the catalysts in one hour. The microstructure of the copolymers has been investigated by ¹H- and ¹³C-NMR spectroscopy. The butadiene is incorporated mainly in 1,4-trans- and 1,2-structure. The high amount of 9-29% of vinyl groups offers the possibility of an easy vulcanisation. The molecular weights of these elastomers are high with values of 250 000. Important is the low glass transition temperature of −28 °C of a copolymer with 7 mol% of butadiene.     

Kristall- und Molekülstruktur von tricarbonyl(η4-3,4-dimethyl-thiophen-1,1-dioxid)eisen

A single-crystal X-ray diffraction study of tricarbonyl(η⁴-3,4-dimethyl-thiophene-1,1-dioxide)iron has been made. Crystal data: space group P4₁2₁2; a  b  9.307(2), c  25.462(5) Å; Z  8. With 950 reflections [F_o > 3 σ(F_o)] the structure has been refined anisotropically (hydrogens isotropically) to R  0.026.In the compound 3,4-dimethylthiophene-1,1-dioxide is coordinated to iron by its diene system analogous to (butadiene)Fe(CO)₃. The sulfur atom is out-of-plane of the butadiene system (26.9°). This fact can be explained by intramolecular repulsion and by coordination effects. The three CO groups are directed towards the centres of greatest electron density in the ring. Hence one CO and the SO₂ group are in eclipsed conformation with a slight deformation due to OO repulsion of both groups. IR, ¹H NMR, and ¹³C NMR data are reported.     

Steric effects in conjugated systems: II. 2,3-Dimethylbutadiene

Based on earlier results of conformational analysis by the Wiberg method¹ of monosubstituted methylbutadienes, analogous calculations for 2,3-dimethylbutadiene have been carried out. Contrary to the opinion of Aten et al.² who assumed almost free rotation, the molecule was shown to exhibit a considerable strain which hinders the rotation of methyl groups and lengthens the C_sp²-C_sp² bond compared with the length of the central bond in butadiene. The calculated lengthening agrees qualitatively with that obtained by electron diffraction¹.     

Facile synthesis of blocky styrene(1,3)‐butadiene copolymers having stereoregular monomeric sequences

Half titanocenes (CpCH₂CH₂O)TiCl₂ 1 and (CpCH₂CH₂ OCH₃)TiCl₃ 2 , activated by methylaluminoxane are tested in styrene–1,3‐butadiene copolymerization. The titanocene 1 is able to copolymerize styrene and 1,3‐butadiene, with a facile procedure, to give products with high molecular weight. The analysis of microstructure by ¹³C‐NMR reveals that the styrene homosequences in copolymers are in syndiotactic arrangement, while the butadiene homosequences are, prevailingly, in 1,4‐cis configuration, according with behavior of 1 in the homopolymerizations of styrene and 1,3‐butadiene, respectively. The reactivity ratios of copolymerization are estimated by diad composition analysis. All obtained copolymers have r₁ × r₂ values much larger than 1, indicating blocky nature of homosequences. The structural characterization by wide‐angle X‐ray powder diffraction and differential scanning calorimetry indicates that all copolymers are crystalline, with T_m varying from 171 to 239 °C, depending on the styrene content. The titanocene 2 did not succeed in styrene–1,3‐butadiene copolymerization, giving rise to a blend of homopolymers. Compounds 1 and 2 were also tested in the polymerization of several conjugated dienes, and the obtained results were very useful to rationalize the behavior of both catalysts in the copolymerization of styrene and butadiene. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 815–822, 2010     

Threshold energies for production of CH2(3B1) and CH2(1A1) from ketene photolysis. The CH2(3B1) ↔ CH2(1A1) energy splitting

By measuring the relative CO quantum yields from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25° for CH₂CO(¹A₁) → CH₂(³B₁) + CO(¹Σ⁺) to be 75.7 ± 1.0 kcal/mole. This corresponds to a value of 90.7 ± 1.0 kcal/mole for ΔH_f298⁰[CH₂(³B₁)]. By measuring the relative ratio of CH₂(¹A₁)/CH₂(³B₁) from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25°C for CH₂CO(¹A₁) → CH₂(¹A₁) + CO(¹Σ⁺) to be 84.0 ± 0.6 kcal/mole. This corresponds to a value of 99.0 ± 0.6 kcal/mole for ΔH_f298⁰[CH₂(¹A₁)]. Thus a value for the CH₂(³B₁) ? CH₂(¹A₁) energy splitting of 8.3 ± 1 kcal/mole is determined, which agrees with three other recent independent experimental estimates and the most recent quantum theoretical calculations.     

Reactivite comparee en catalyse redox de plusieurs telogenes halogenes vis-a-vis du butadiene

Using copper chloride as catalyst, we have achieved telomerization of butadiene with several different halogenated compounds as telogens. These telogens must have a CCl₃ group to be active as transfer agents. There is a linear relationship between log (telogen reactivity) and the σ¹ Taft constant of the R group. Using this relation, we have determined the values of the σ¹ constants for some halogenated substances. The reactivities of the telogens can be measured by this means. The results confirm those obtained earlier with styrene.     

Singlet methylene kinetics: Direct measurements of removal rates of ã1A1 and b̃1B1 CH2 and CD2

Rate constants for collisional removal of ã¹A₁ and b?¹B₁ CH₂ and CD₂ have been directly measured, using IR laser induced multiple photon dissociation to prepare the radicals, and time resolved laser induced fluorescence to observe them. For CH₂(ã¹A₁) removal by He, Ne, Ar, Kr, Xe, N₂, H₂, O₂, CO and CH₄, rate constants of 3.1, 4.2, 6.0, 7.0, 16, 8.8, 130, 30, 56 and 73 × 10^?12 cm³ molecule^?1 s^?1 were found respectively. These represent significant increases over the previously accepted values. Essentially no isotope effect is observed in the removal of CD₂(ã¹A₁) by the rare gases. The rate determining step in removal by the rare gases and N₂ is thought to be singlet—triplet intersystem crossing controlled by long range attractive forces, and the results are discussed in terms of both isolated and mixed state theoretical models of these processes. For the other molecular collision partners, bimolecular chemical removal channels are possible, and may account for the relatively fast rates observed. Radiative lifetimes of five Σ vibronic levels of CH₂(b?¹B₁) and three Σ vibronic levels of CD₂(b?¹B₁) have been measured and found to lie in the range 2.5–6.0 μs, and collisional quenching rates for CH₂(b?¹B₁) are found to be of the order of the gas kinetic collisional frequency.     

Multiphoton ionisation spectroscopy of H2S: a reinvestigation of the 1B1-1A1 band at 139.1 nm

The 3 + 1 multiphoton ionisation (MPI) spectrum of the ¹B₁-¹A₁ transition in H₂S at 139.1 nm has been recorded in both linearly and circularly polarised light. The rotational structure shows marked differences from that of the one-photon absorption spectrum. Properties of the excited state revealed through analysis of this structure include confirmation of its ¹B₁ character, refined values for its A, B and C rotational constants and the operation of an energy-dependent predissociation mechanism. It is shown that the third-rank tensor component of the transition operator dominates over the first-rank component in this MPI band. The orbital nature of this ¹B₁ excited state is considered.     

Darstellung und Untersuchung von Aminoschwefeltrifluoriden sowie eines Hydrolyseprodukts, 1-(Fluorooxothio)-2,5-dihydropyrrol

Synthesis and Investigation of Aminosulphur Trifluorides and of a Hydrolysis Product 1-(Fluorooxothio)-2,5-dihydropyrrole The reaction of previously unknown (trimethylsilyl)amines with sulphur tetrafluoride gives some new aminosulphurtrifluorides. Experiments to cleaver 1-(Trifluorothio)-2,5-dihydropyrrole and 1-(trifluorothio)pyrrolidin into butadiene and ethylene respectively and NSF₃ by way of a chelotrope cycloelimination were unsuccessful. ¹H-NMR and ¹⁹F-NMR spectra revealed the nitrogen in the aminosulphur trifluorides must be regarded sp³ hybridized rather than sp².     

Copolymerization of propylene with 1,3‐butadiene using isospecific zirconocene catalysts

Poly(propylene‐ran‐1,3‐butadiene) was synthesized using isospecific zirconocene catalysts and converted to telechelic isotactic polypropylene by metathesis degradation with ethylene. The copolymers obtained with isospecific C₂‐symmetric zirconocene catalysts activated with modified methylaluminoxane (MMAO) had 1,4‐inserted butadiene units ( 1,4‐BD ) and 1,2‐inserted units ( 1,2‐BD ) in the isotactic polypropylene chain. The selectivity of butadiene towards 1,4‐BD incorporation was high up to 95% using rac‐dimethylsilylbis(1‐indenyl)zirconium dichloride (Cat‐A)/MMAO. The molar ratio of propylene to butadiene in the feed regulated the number‐average molecular weight (M_n) and the butadiene contents of the polymer produced. Metathesis degradations of the copolymer with ethylene were conducted with a WCI₆/SnMe₄/propyl acetate catalyst system. The ¹H NMR spectra before and after the degradation indicated that the polymers degraded by ethylene had vinyl groups at both chain ends in high selectivity. The analysis of the chain scission products clarified the chain end structures of the poly(propylene‐ran‐1,3‐butadiene). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5731–5740, 2007