Isomer distinction by ion/molecule reactions in an ion trap: The case of C5H8

Isomeric C₅H₈ compounds are distinguished by monitoring the products of their reactions with mass-selected ions generated from the individual isomers. This procedure, done by selecting appropriate reaction times in a quadrupole ion trap, yields data for the compounds which are more structure-selective than those obtained by collision-induced dissociation or dissociative charge stripping, both procedures in which isomer distinction is based on the behavior of the molecular ions rather than the neutral molecules themselves. All isomers except cis and trans 1,3-pentadiene can be distinguished by their ion/molecule reactions. The conjugated dienes, 1,3-pentadiene and isoprene, form the deprotonated C₁₀H₁₅⁺ dimer which is not generated by 1,4-pentadiene, cyclopentene, or by the allenes, 2,3-pentadiene and 3-methyl-1,2-butadiene. This clear, qualitative difference enables the isomers 1,4- and 1,3-pentadiene to be distinguished, which is otherwise difficult.     

Chemoselectivity in 4-methyl-1,3-pentadiene polymerization in the presence of homogeneous Ti-based catalysts

The homogeneous catalyst CpTiCl₃-MAO is able to produce a random copolymer of 4-methyl-1,3-pentadiene with ethylene. ¹³C NMR analysis of the copolymers shows that after insertion of ethylene units, the next 4-ymethyl-1,3-pentadiene unit can be inserted in either 1,2 or 1,4 arrangement. The high chemoselectivity observed in the 1,2-syndiotactic homopolymerization of 4-methyl-1,3-pentadiene with respect to the lower one observed in the copolymerization with ethylene is attributed to a back-biting coordination to the Ti of the active species of the penultimate monomer unit of the growing chain.     

Selective carbometallation of α,β-unsaturated carbonyl compounds and substituted oxacyclopropanes with zirconium-diene complexes

The reactions of zirconium-dience complexes, ZrCp₂(s-cis-diene), with bifunctional electrophiles, i.e. α,β-unsaturated ketones, unsaturated esters and substituted oxacyclopropanes, were investigated. Reaction of ZrCp₂(s-cis-isoprene) with an equivalent of 3-buten-2-one or alkyl acrylates, selectively gives 1,2-addition products. CC bond formation occured at the C(1) atom of the isoprene moiety whereas 1,3-pentadiene-, 2-methyl-1,3-pentadiene- and 2,4-dimethyl-1,3-pentadiene complexes induced the regioselective 1,2-addition at the C(4) position of the diene moiety. Phenyloxacyclopropane and 2-methyl-3-phenyl-oxacyclopropane also react with ZrCp₂(isoprene) leading to CC bond formation from the C(1) atom of isoprene to the oxirane carbon bearing the phenyl group. The corresponding reactions of 2-methyl-2-butene-1,4-diylmagnesium with α,β-unsaturated carbonyl compounds were also studied and found to give quite different products.     

Assignments of the vibrational spectra of 2,5-dimethyl-2,4-hexadiene, 4-methyl-1,3-pentadiene and (E)-2-methyl-1,3-pentadiene. Effect of the terminal and lateral methyl groups

The complete assignment of the vibrational spectra of 2,5-dimethyl-2,4-hexadiene, 4-methyl-1,3-pentadiene and (E)-2-methyl-1,3-pentadiene was obtained from a comparative analysis of their i.r. and Raman spectra (solid, liquid and gas) in the range 3200-50 cm⁻¹. It is shown that particular vibrational motions strongly interact to give rise to very characteristic modes depending on the site of methyl substitution. The comparison of our results with those of analogous shorter and larger polyenes and polyenals allows us to discuss the various local coupled motions characteristic of unsubstituted (CHCH CH)CH and methyl substituted (CHC(CH₃)CH), ((CH₃)₂CCH) or (CH₃CHCH) fragments in polyenic chains.     

Influence of monomer structure on chemo- and stereoselectivity of 1,3-diene polymerization

MAO/CpTiCl₃ is an active catalyst for the polymerization of various types of 1,3-dienes. Butadiene, (E) - and (Z) −1,3-pentadiene, (E) −2-methyl-1,3-pentadiene and 2,3-dimethylbutadiene yield, at room temperature, polymers with a cis-1,4 or a mixed cis/1,2 structure. 4-Methyl-1,3-pentadiene and (E,E) −2,4-hexadiene give, respectively, a 1,2 syndiotactic and a trans-1,4/1,2 polymer. MAO/CpTiCl₂·2THF and MAO/(CpTiCl₂)_n are less active than the CpTiCl₃ catalyst, but give the same type of polymers. A change of stereospecificity with temperature was observed in the polymerization of (Z)-1,3-pentadiene: a cis-1,4 isotactic polymer was obtained at +20°C, and a crystalline 1,2 syndiotactic polymer at −20°C. This effect was attributed to a different mode of coordination of the monomer, which is cis-η⁴ at +20°C and may be trans-η² at −20°C. Results obtained with catalysts from CpTi(OBu)₃ and Ti(OBu)₄ are reported for comparison. An interpretation is given of the formation of cis-1,4 isotactic poly(2-methylpentadiene) and of 1,2 syndiotactic poly(4-methylpentadiene), as well as of syndiotactic polystyrene.     

Gehinderte ligandbewegungen in übergangsmetallkomplexen: XXX. Synthese und dynamisches verhalten von tricarbonyl-η4-dien-trimethylphosphit-wolfram(0)-komplexen

UV irradiation of [W(CO)₅P(OCH₃)₃] (I) in the presence of 1,3-butadiene (II), (E)-1,3-pentadiene (III), 2-methyl-1,3-butadiene (IV), (E,E)-2,4-hexadiene (V), 2- methyl-1,3-pentadiene (VI) and 1,3-cyclohexadiene (VII) yields the [W(CO)₃- P(OCH₃)₃(η⁴-diene)] complexes (VIII–XIII). While VIII–XII form predominantly facial isomers in the a-form, the 1,3-cyclohexadiene complex XIII exists in both possible facial a- and f-forms, which have different relative positions of the P(OCH₃)₃ ligand towards the η⁴-diene moiety. XIII shows therefore two different hindered ligand mobilities, an a–f-isomerization (ΔG₂₀₀³ 36.2 ± 0.2 kJ/mol) and a carbonyl scrambling (ΔG₂₅₀³ 50.6 ± 0.2 kJ/mol) such as the other complexes VIII–XII. These ligand movements were studied by temperature dependent ¹³C and ³¹P NMR spectra. VIII–XIII were further characterized by IR and ¹H NMR spectroscopy and C, H elemental analyses.     

Polymerization of 1,3-butadiene, 4-methyl-1,3-pentadiene and styrene with catalyst systems based on biscyclopentadienyl derivatives of titanium

1,3-Butadiene, 4-methyl-1,3-pentadiene and styrene were polymerized with dicyclopentadienyltitanium dichloride/methylaluminoxane (Cp₂TiCl₂/MAO) and dicyclopentadienyltitanium chloride/MAO (Cp₂TiCl/MAO). These systems are less active than cyclopentadienyltitanium trichloride/MAO (CpTiCl₃/MAO), but show the same stereospecificity as the latter; they give predominantly cis-1,4-polybutadiene, 1,2-syndiotactic poly(4-methyl-1,3-pentadiene) and syndiotactic polystyrene. Cp₂TiCl/MAO is much more active than Cp₂TiCl₂/MAO; this is probably due to the fact that in the reaction of Cp₂TiCl₂ with MAO, only a small amount of Ti(IV) is reduced to Ti(III), which is the active species in the polymerization of styrene and 1,3-dienes. An interpretation of the structure of the active species in Cp₂TiCl/MAO is reported.     

Asymmetric radiation-induced inclusion polymerization of 3-methyl-1,4-pentadiene in deoxycholic acid

The radiation-induced polymerization of 3-methyl-1,3-pentadiene (3MPD) as an inclusion complex in deoxycholic acid (DOCA) has produced in good yield the optically active polymer poly(3-methyl-1,4-pentadiene) (P3MPD) whose structure and properties were studied by FT-IR spectroscopy and thermal analysis (TGA, DTG and DTA). The data show that the polymer is essentially trans-1,4-P3MPD as expected for the polymerization in constrained media. Trans-1,4-P3MPD is optically active with [α]_D values comprised between +4.3 and +5.6. The optical rotatory dispersion curve of the P3MPD is completely different from that of DOCA as expected.     

On the mechanism of formation of isotactic and syndiotactic polydiolefins

The mode of formation of isotactic and syndiotactic polymers from 1,3-dienes is examined in the light of the most recent results. An interpretation is given for the formation of trans-1,4 isotactic polymers from CH₂=CH-CH=CHR (R = Me, Et, Pr, etc.) type monomers with heterogeneous VCl₃-based catalysts. Evidence is reported showing that stereoregular 1,2 or cis-1,4 polymers derive from a growing polymer chain anti-η³-bonded to the transition metal and a cis-η⁴ coordinated monomer. The influence on stereoselectivity of the substituents at the central carbon atoms of the monomer is discussed. The peculiar behavior of (Z)-1,3-pentadiene and 4-methyl-1,3-pentadiene, which give 1,2 polymers with catalysts that give 1,4 polymers from other monomers, is attributable to the fact that they can coordinate trans-η², in addition to cis-η⁴.     

Stereochimie d'heterocycles du groupe IVB—II : Syntheses stereoselectives d'hydrogeno-1 et d'alkyl-1 sila-1 cyclobutanes

The reaction between n-butyllithium and 1,2 (or 1,3)-dimethyl-1-t-butoxy-1-silacyclobutanes proceeds with retention of configuration at silicon, and yields 10/90 (or 80/20) Z/E mixture of 1,2 (or 1,3)-dimethyl-1-n-butyl-1-silacyclobutanes. Methylation of 2 (or 3)-methyl-1-t-butoxy-1-silacyclobutanes (Z/E = 15/85 or 65/35) by methylmagnesium iodide gives 15/85 (or 65/35) Z/E mixture of 1,2 (or 1,3)-dimethyl-1-silacyclobutanes. The proposed configurations for substituted silacyclobutanes are supported by spectroscopic data (RMN) and chemical results (correlation of configuration and stereomutation of hydrogenosilacyclobutanes).     

Crystalline isotactic trans-1,4-poly(1,3-pentadiene). Explanation of a stress-induced conformational transition

A conformational energy analysis is performed in order to explain the different conformations assumed by isotactic trans-1,4-poly(1,3-pentadiene) when crystallized under stretching conditions or not. The basic idea is that, while in an unstretched sample any configurational defect on the tertiary carbon atoms may be confined in the interlamellar region, stress-induced crystallization enhances the probability of configurational defects being embedded within an ordered environment. Results clearly indicate the cis-conformation as the most suitable to overcome conformational strains induced by defects in the crystalline phase, while the skew-conformation is preferred in an ordered environment.     

Chain transfer by addition-fragmentation mechanism—9. access to diene-functional macromonomers using 5-(substituted)-1,3-pentadiene-type addition-fragmentation chain-transfer agents in radical polymerization

Radical polymerizations of methyl methacrylate (MMA) and styrene (St) in bulk at low conversion were carried out in the presence of pentadienic chain transfer agents (CTA), 5-bromo-1,3-pentadiene (1), 5-benzenesulphonyl-1,3-pentadiene (2) and methyl 2-bromomethyl-4-methyl-2,4-pentadienoate (3), to produce conjugated diene-end capped macromonomers by a addition-fragmentation mechanism. The chain-transfer constants (C_ir) of 1, 2 and 3 for MMA polymerization were obtained from the Mayo equation, respectively. Correction to zero conversion afforded an accurate value of the chain transfer constant for 1. The chain transfer was found to be degradative. The pentadienyl group formed by fragmentation of the macroradical abduct is quantitatively introduced at the ω-end of the polymer.     

Synthesis with 1,2-Oxazines. II. Synthesis and Properties of 2,3-dimethyl-5,6-dihydro-4H-1,2-oxaziniumiodide

Preparation of 2,3-Dimethyl-5,6-dihydro-4H-1,2-oxaziniumiodide was achieved by N-alkylation of 3-methyl-5,6-dihydro-4H-1,2-oxazine. Reactions with C-nucleophiles led to the corresponding N-methyl-perhydro-1,2-oxazine derivatives. Reaction with sodium hydride in triglyme led to 3-methyl-4-aza-1,3-pentadiene.     

Crystallization Behaviors and Regime Kinetics Analysis of Poly(<Emphasis Type="Italic">L</Emphasis>-lactide)-poly(butylene adipate)-poly(<Emphasis Type="Italic">L</Emphasis>-lactide) Based Multiblock Thermoplastic Polyurethanes

Poly(L-lactide)-based (PLLA) poly(ester-urethane)s are particularly relevant and gain significant attention due to their environment-friendly degradability and elastomeric shape memory capability. The tensile properties, resilience and degradation are strongly affected by their crystallization. This work was to investigate crystallization behaviors of the poly(L-lactide)-poly(butylene adipate)-poly(L-lactide) (PLLA-PBAPLLA) based thermoplastic polyurethane elastomers (PLAEUs) we synthesized previously. Dynamic scanning calorimetry (DSC) and polarized optical microscopy (POM) in combination with Avrami, Jezioney and Hoffman-Weeks models were used to analyze the impact of the PLLA block length on the crystallization temperature T_c, degree of crystallinity X_c, nucleation and spherulite growth mode and crystallization regime kinetics of the PLAEUs. The results indicate the low melting point poly(butylene adipate) (PBA) block resides in the amorphous domains while the PLLA block resides in both crystalline and amorphous phases. The X_c of the PLAEUs increase with the increased length of the PLLA block (i.e. higher content of PLLA block). The analyses with Avrami and Jezioney models show the PLAEU copolymers follow a disc-like spherulite growth. The covalently bonded PBA block decreases both nucleation velocity and spherulite growth rate in the isothermal crystallization. Such an impact is lessened as PLLA block length increases. The PLLA homopolymers demonstrate crystallization regime transition from II to III at a certain T_c of isothermal crystallization, while the crystallization regime kinetics of PLLA block in the PLAEUs are explained by a single regime III at low molecular weights of PLLA and the transition is restored as the PLLA block length increases (i.e. regime II to III).     

Isothermal crystallization kinetics of poly(ethylene terephthalate)s of different molecular weights

The isothermal crystallization kinetics and morphology of poly(ethylene terephthalate) (PET) polymers of different molecular weights have been studied by means of differential scanning calorimetry and transmission microscopy (TM). The kinetic parameters of Avrami exponent n, the rate constant k, half time t _1/2, rate at 50 % crystallinity, τ _1/2 for crystallization of different PETs were evaluated from double logarithmic plots of log {?ln[1 ? X(t)]} versus log t, where X(t) is extent of crystallinity at a given crystallization temperature. The crystallization rate of polymers with high molecular weight found to be lower than that of polymers with low molecular weight, at the same crystallization temperature. It was found that the nucleation mechanism and growth dimension of polymers with low molecular weight are different from those of polymers with high molecular weight. The results of TM and isothermal crystallization kinetics showed a consistent trend for the crystallization of all PET polymers studied, comprising a primary stage and a secondary stage. The activation energy in the PET polymers of low molecular weight was found to be lower than that of polymers with high molecular weight.     

Effect of nanoscale fully vulcanized acrylic rubber powders on crystallization of poly(butylene terephthalate): Isothermal crystallization

Poly(butylene terephthalate) (PBT) was blended with nanoscale fully vulcanized acrylic rubber (FVAR) powders in a twin extruder, and the FVAR powders were dispersed well in PBT from scanning electron microscopy (SEM) and transmission electron microscope (TEM) investigation. The isothermal crystallization kinetics of PBT/FVAR blends were investigated by differential scanning calorimeter (DSC) and simulated by Avrami model. Equilibrium melting temperature was estimated by the nonlinear Hoffman-Weeks relation. The active energy (ΔE) and nucleation parameters (K_g) increased with the addition of FVAR, suggesting that FVAR particles hindered the crystallization; however more content FVAR had a lower ΔE and K_g because FVAR powders acted as heterogeneous nuclei in the nucleation of crystallization and facilitated the crystallization of PBT. The crystallization ability followed the order: PBT > PBT/FVAR6 > PBT/FVAR3 > PBT/FVAR1 when undercooling was considered.     

未添加晶种结晶过程的中后期动力学模拟

以KNO₃-H₂O为模型体系, 考察了未添加晶种的间歇结晶过程动力学, 将历经爆发成核后的结晶体系近似为添加晶种的结晶体系. 并结合光学关联方法, 推导了可描述历经爆发成核后的晶体形成和生长速率模型. 模型中含有可反映结晶固相信息的透光率变量, 从而避免了以往模型仅靠液相浓度数据求解模型参数的不便. 运用该模型拟合未添加晶种结晶过程的中后期实验数据, 得到了KNO₃晶体的二次成核和生长动力学参数, 参数结果与文献中报道的添加晶种结晶过程的参数值相近. 在此基础上, 针对添加晶种的结晶过程, 提出了晶种添加量的定量设计方法, 并得到了实验的初步验证.     

Crystallization and melting behaviors of polystyrene-b-poly(ethylene-co-butene) block copolymers

Non-isothermal and isothermal crystallization behaviors of polystyrene-b-poly(ethylene-co-butene) (PSt-b-PEB) block copolymers with different compositions and chain lengths were investigated by differential scanning calorimetry (DSC). The results show that crystallization of PEB block is strongly dependent on the composition. Crystallization temperature (T_c), melting temperature (T_m) and fusion enthalpy (ΔH_f) increase rapidly with PEB volume fraction (V_E) for block copolymers with V_E below 50%, but there is little change when PEB block becomes the major component. Glass transition temperature (T_g) of the PSt block and order-disorder transition temperature (T_ODT) of block copolymers also have a weak effect. The isothermal crystallization kinetics results show that Avrami exponent (n) was strongly dependent on the composition and crystallization temperature. For the block copolymers with V_E below 38.7 vol%, the values of n vary between 0.9 and 1.3, indicating that crystallization is confined. For the PSt-b-PEB block copolymers with V_E higher than 50%, fractionated crystallization behavior is usually observed. A two-step isothermal crystallization procedure is applied to these block copolymers. It is found that breakout crystallization occurs at higher T_c, but confined at lower T_c. Two overlapped melting peaks are observed for the block copolymers with fractionated crystallization behavior after two-step crystallization, and only the higher melting peak corresponding to breakout crystallization can be used to derive equilibrium melting temperature.     

Linear oligomerization of 1,3-pentadiene in presence of catalytic system CoCl2-PPh3-NaBH4

Conclusions The system CoCl₂-PPh₃₂-NaBH₄ catalyzes the oligomerization of trans-1,3-pentadiene to 4-methyl-2,5,7-nonatriene and the 1,3-pentadiene trimer. 4-Methyl-2,5,7-nonatriene is formed predominantly at 95°, while the trimer is the predominant product at 120°. This system does not catalyze the oligomerization of cis-1,3-pentadiene.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, 1423–1425, June, 1978.     

Effect of in impurity on crystallization kinetics of (Se.7Te.3)100−xInx system

The effect of In impurity on the crystallization kinetics and the changes taking place in the structure of (Se₇Te₃) have been studied by DTA measurements at different heating rates (α=5 deg·min^?1, 10 deg·min^?1, 15 deg·min^?1 and 20 deg·min^?1). From the heating rate dependence of the values ofT _g,T _c andT _p, the glass transition activation energy (E _t) and the crystallization activation energy (E _c) have been obtained for different compositions of (Se₇Te₃)_100?xIn_x (0≤×≤20). The variation of viscosity as a function of temperature has been evaluated using Vogel-Tamman-Fulcher equation. The crystallization data are analysed using Kissinger's and Matusita's approach for nonisothermic crystallization. It has been found that for samples containing In=0, 10, 15, 20 at%, three dimensional nucleation is predominant whereas for samples containing In=5 at%, two dimensional nucleation is the dominant mechanism. The compositional dependence ofT _g and crystallization kinetics are discussed in terms of the modification of the structure of the Se?Te system.