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.     

Cationic polymerization of 1,3-pent adiene in the presence of arenes

The cationic polymerizations of 1,3-pentadiene initiated by AlCl3 in n-hexane at 30℃ have been carried out in the presence of various arenes,i.e.,benzene,toluene,p-xylene,o-xylene,m-xylene and mesitylene.The presence of all these arenes have reduced in different degrees the formation of crossliuked products.Namely,the crosslinking reaction,a major side-reaction during the cationic polymerization of 1,3-pentadiene,has been suppressed by adding the aromatic compounds.The results showed that a chain transfer to arene took place and this transfer process hindered the generation of the crosslinked polymer.IR and 1H NMR spectra have confirmed the existence of the corresponding aryl groups in the resulting polymers.     

Thermal behavior of syndiotactic E-1,2-poly(3-methyl-1,3-pentadiene)

Syndiotactic E-1,2-poly(3-methyl-1,3-pentadiene) was synthesized with the catalyst system Fe(bipy)₂Cl₂-MAO. The thermal stability and kinetic parameters of degradation were determined by thermogravimetric analysis. The isothermal crystallization kinetics were described by means of the Avrami equation, which suggested a three-dimensional growth of crystalline units, developed by heterogeneous nucleation, followed by a secondary crystallization stage. Syndiotactic E-1,2-poly(3-methyl-1,3-pentadiene) isothermally crystallizes from the melt according to regime II of crystallization described by Lauritzen-Hoffman secondary nucleation theory. Non-isothermal crystallization kinetics were elaborated using different approaches. The equilibrium melting temperature was calculated. The kinetic and thermodynamic data were compared with those obtained from syndiotactic 1,2-poly(1,3-butadiene), which is the first example of 1,2 polydienes family.     

Alkylation of toluene with 1,3-pentadiene catalyzed by [bupy]BF4-AlCl3 and [bupy]BF4-FeCl3 ionic liquids

A new application of ionic liquids is developed for a novel process of synthesizing pentyltoluene from toluene and a C5 diolefin (1,3-pentadiene). The catalyst [bupy]BF₄-AlCl₃ behaves better than [bupy]BF₄-FeCl₃.     

Allyl chloride/AIC13/ether cationic initiating systems for polymerization of 1,3-pentadiene

Various ethers were used to mediate the polymerization of 1,3-pentadiene (PD) initiated by AlCl₃ and by allyl chloride (AllyCl)/AlCl₃. The introduction of the ethers exert considerable effects on polymer yield and molecular weight due to its interaction with the propagating carbocation. The carbocation reactivity is reduced by this interaction which is subject to the ether's nucleophilicity determined by the steric hindrance of groups adjacent to oxygen. The reduction of carbocation reactivity gives rise to a decrease of polymer yield owing to inhibition of propagation but results in an augmentation of molecular weight due to suppression of various side reactions such as terminations. By using suitably nucleophilic ethers such as diphenyl ether, the polymerization can be mediated to give an high molecular weight polymer in high yield.     

Cationic polymerization of cyclic dienes. X. Cationic polymerization of 1-vinylcyclohexene and 3-methyl-1,3-pentadiene

1-Vinylcyclohexene (VCH), which has one of the double bonds in the ring and the other outside the ring, was synthesized and polymerized by cationic catalysts. The reactivity of VCH was very large in the polymerizations catalyzed by boron trifluoride etherate (BF₃OEt₂) and stannic chloride–trichloroacetic acid complex. Similar to other cyclic dienes, the polymerization of VCH was a nonstationary reaction having a very fast initiation step. The polymerization proceeded by either a 1,2- or a 1,4-propagation mode in which vinyl group was always involved. Particularly when BF₃OEt₂ was used as a catalyst, an intramolecular proton or an intramolecular hydride ion transfer reaction took place, resulting in the formation of methyl groups in the polymer. The degree of polymerization of polymer formed was about 10. This indicates the preponderance of monomer transfer reaction. To investigate the reason for the high reactivity of cyclic dienes, cationic copolymerizations of VCH and 3-methyl-cis/trans-1,3-pentadiene (cis/trans-MPD) was carried out. The relative reactivity of monomers decreased in the order VCH > trans-MPD > cis-MPD. On the other hand, the resonance stabilization of monomers decreased in the order VCH > trans-MPD > cis-MPD. Therefore, it could be considered that the monomer reactivity is mainly determined by the stability of carbonium ion intermediate. The relative stability of carbonium ion must be VCH > trans-MPD > cis-MPD. Thus the influence of the conformation of ion on its stability was clearly demonstrated.     

~(13)C-NMR STUDY ON THE CHAIN TERMINAL STRUCTURE OF POLY-1,3-PENTADIENE POLYMERIZED WITH RARE EARTH CATALYST

The sequence distribution and the terminal structures of poly-1,3-pentadiene chains obtained by rare earth catalyst and effect of polymerization temperature on microstructure of the polymer have been investigated by ~(13)C-NMR method. According to experimental results it was supposed that terminal active growing chain of the polymer would be four types of anti- and syn-η~3-allyl structures. When polymerization temperature was reduced, the content of cis-1,4-poly-1,3-pcntadiene increases. It can be explained by isomerization between anti- and syn-η~3-allyl. The process forming trans-1,2 unit instead of 3,4-unit were also described.     

Application of Et3NHCl-AlCl3 ionic liquid as an initiator in cationic copolymerization of 1,3-pentadiene with styrene

Cationic copolymerization of 1,3-pentadiene (PD) with styrene (St) using the triethylamine hydrochloride-aluminium chloride (Et₃NHCl-AlCl₃) room temperature ionic liquid as an initiator in toluene has been investigated. The polymerization proceeds to high conversions, indicating high initiating reactivity of Et₃NHCl-AlCl₃ in these copolymerization systems, although molecular weights of the polymers are limited which are similar to polymerization initiated by Lewis acids such as TiCl₄, BF₃, BF₃·OEt₂. The polymers were analyzed using IR spectra in conjunction with gel permeation chromatography (GPC).     

Allyl chloride/AlCl_3/ether cationic initiating systems for polymerization of 1,3-pentadiene

Various ethers were used to mediate the polymerizations of 1,3-pentadiene (PD) initiated by AlCl3 and by allyl chloride (AllyCl)/AlCl3. The introduction of the ethers exert considerable effects on polymer yield and molecular weight due to its interaction with the propagating carbocation. The carbocation reactivity is reduced by this interaction which is subject to the ether's nucleophilicity determined by the steric hindrance of groups adjacent to oxygen. The reduction of carbocation reactivity gives rise to a decrease of polymer yield owing to inhibition of propagation but results in an augmentation of molecular weight due to suppression of various side reactions such as terminations. By using suitably nucleophilic ethers such as diphenyl ether, the polymerization can be mediated to give an high molecular weight polymer in high yield.     

Metal‐Free Hydrogenation Catalyzed by an Air‐Stable Borane: Use of Solvent as a Frustrated Lewis Base

In recent years ‘frustrated Lewis pairs’ (FLPs) have been shown to be effective metal‐free catalysts for the hydrogenation of many unsaturated substrates. Even so, limited functional‐group tolerance restricts the range of solvents in which FLP‐mediated reactions can be performed, with all FLP‐mediated hydrogenations reported to date carried out in non‐donor hydrocarbon or chlorinated solvents. Herein we report that the bulky Lewis acids B(C₆Cl₅)_x(C₆F₅)_3?x (x=0–3) are capable of heterolytic H₂ activation in the strong‐donor solvent THF, in the absence of any additional Lewis base. This allows metal‐free catalytic hydrogenations to be performed in donor solvent media under mild conditions; these systems are particularly effective for the hydrogenation of weakly basic substrates, including the first examples of metal‐free catalytic hydrogenation of furan heterocycles. The air‐stability of the most effective borane, B(C₆Cl₅)(C₆F₅)₂, makes this a practically simple reaction method.     

Copolymerization of styrene with (Z)-1,3-pentadiene in the presence of a syndiotactic-specific catalyst

Copolymerization of styrene with (Z)-1,3-pentadiene affords copolymers mostly containing 1,2 pentadiene units. Both the styrene and the pentadiene units are in syndiotactic arrangement but the comonomer sequence distribution is far from bernoullian. Interestingly, the behavior of (Z)-1,3-pentadiene does not change much when polymerization temperature raises from −20 to +20°C, notwithstanding that (Z)-1,3-pentadiene affords a 1,2-syndiotactic homopolymer at −20°C but a prevailingly 1,4 cis homopolymer at +20°C. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2697–2702, 1997     

Photodissociation of gaseous [C5H8]+˙ ions

Photodissociation permits the distinction of four isomeric [C₅H₈]^+˙ ions (ionized 2-pentyne, 1,2-pentadiene, 1,3-pentadiene and cyclopentene) which cannot be identified via collisional activation spectrometry. Both the relative cross-section for photodissociation and the relative abundance of the photodissociated fragments can be used to characterize the ion structure. Furthermore, upper and lower limits for the barrier for interconversion between 1,3-pentadiene and the other isomers can be determined.     

rac-[CH2(3-tert-butyl-1-indenyl)2]ZrCl2/MAO in the Copolymerization of Olefins and Dienes

Olefin-diene copolymerizations in the presence of C₂ symmetric zirconocene rac-[CH₂(3-tert-butyl-1-indenyl)₂]ZrCl₂/MAO catalytic system have been reported and rationalized by experimental and molecular modeling studies. Ethene gives 1,2-cyclopropane and 1,2-cyclopentane, 1,3-cyclobutane, and 1,3-cyclopentane units in copolymerization with 1,3-butadiene, 1,4-pentadiene, and 1,5-hexadiene, respectively. Propene-1,3-butadiene copolymerizations lead to 1,2 and 1,4 butadiene units and to a low amount of 1,2-cyclopropane units.     

Silver and palladium nanoparticles-containing products of the low-temperature wave conversion of an energetic material: Catalytic activity in piperylene hydrogenation

The hydrogenation of 1,3-pentadiene into pentenes over the commercial 0.5% Pd/Al₂O₃ catalyst and over a new catalyst containing 1.0% Pd and 3.7% Ag (μ-catalyst) has been investigated. The new catalyst has been prepared via the flameless wave conversion of cyclotrimethylenetrinitramine in a porous composite. The catalytic properties of the new composite in the hydrogenation reaction depend on the hydrogen/1,3-pentadiene ratio and on the catalyst activation temperature. The reaction conditions for selective 1,3-pentadiene hydrogenation have been optimized. The pentenes yield as a function of temperature passes through a maximum at any H₂/C₅H₈ ratio between 1 and 2. The 2-pentene/1-pentene ratio in the reaction products increases as the temperature is raised.     

Phosphine-Catalyzed Annulations between Modified Allylic Derivatives and Polar Dienes and Substituent Effect on the Annulation Mode

in this work, the phosphine-catalyzed annulation reactions between modified allylic derivatives and polar 1,1-dicyano-1,3-dienes have been studied. In the catalysis of PPh3 （20 mol%）, a [4 ＋ 1 ] annulation reaction is realized between a series of l,l-dicyano-2,4-diaryl-1,3-dienes and ethoxycarbonyl-activated allylic acetate, producing polysubstituted cyclopentenes in modest to excellent yields. It is also observed that the substituents of both 1,3-dienes and allylic derivatives have a significant influence on the annulation mode： under the catalysis of PPh3 or PBu3 （20 mol%）, regioselective [3 ＋ 2] annulation products are formed from differently substituted substratcs.     

Reactivity variations within Group 4 complexes of 1,4-di-tert-butyl-1,4-diazabuta-1,3-diene: Structures of [(C5H5)TiCl{(t-BuNCH)2}] and [(C5H5)2Zr{(t-BuNCH)2}]

The reactions of the metallocene dichlorides [(η⁵-C₅H₅)₂MCl₂], M = Ti and Zr, with the 1,4-di-tert-butyl-1,4-diazabuta-1,3-diene radical anion (lithium complex) in diethyl ether reveal a reactivity difference within the series, yielding [(C₅H₅)TiCl{(t-BuNCH)₂}] and [(C₅H₅)₂Zr{(t-BuNCH)₂}] through the elimination of Li(C₅H₅) and/or LiCl, respectively. We report the X-ray crystal structures of these complexes, and discuss their reactivity patterns and solution fluxional properties.     

Efficient epoxidation of terminal and internal alkenes using t-butylhydroperoxide catalysed by polybenzimidazole-supported Mo(VI).(PBI.Mo)

A polybenzimidazole-supported Mo complex (PBI.Mo) has been prepared by a method already reported. Extensive investigation of digestion procedures has shown a dry-ashing method using NaNO₃/HNO₃ (conc.) at 560°C to be an optimal method for preparing samples for Mo analysis by atomic absorption spectrophotometric methodology. Mo loadings in the range 1.32–0.62 mmol Mo g⁻¹ polymer were demonstrated. PBI.Mo has been used as a heterogeneous catalyst in the epoxidation of cyclohexene, methylene-cyclohexane, 4-vinyl cyclohexene, styrene, 1,3-pentadiene and allyl chloride, bromide and alcohol using t-butylhydroperoxide as the oxidant. The catalyst is very effective for the first four substrates, somewhat less active than soluble MoO₂acac₂, but providing final yields and purity of products generally better than using MoO₂acac₂. The 1,3-pentadiene displays an overall conversion of ∼35% with a distribution of the four possible monoepoxide isomers similar to that obtained with MoO₂acac₂ as catalyst. The allylic substrates showed poor conversion probably as a result of secondary (oligomerisation) reactions involving the epoxide products. Running the epoxidations for extended periods in air allows in situ generation of alkyl hydroperoxides in the case of cyclohexene and 4-vinylcyclohexene and these are then effective internal oxidants for further Mo catalysed epoxidation of these alkenes. When run under anaerobic conditions the reactions are very clean with no evidence of any free radical processes contributing. In all cases Mo leaching is minimal. Good activity is seen in the recycling of PBI.Mo in the case of styrene and 1,3-pentadiene, although with cyclohexene and 4-vinylcyclohexene steady deactivation is seen, probably as a result of catalyst fouling. Thermogravimetric analyses suggest that it might be possible to burn off the foulant without destroying the catalyst.     

Tris(acetonitrile)tricarbonylchromium(0) catalyzed 1,4-addition of hydrogen to 1,3-dienes

The Cr(CO)₃(CH₃CN)₃ complex is found to catalyze the 1,4-addition of hydrogen to 1,3-dienes such as 2-methyl-1,3-butadiene, trans-1,3-pentadiene, and trans, trans-2,4-hexadiene at low temperature (40°) and low H₂ pressure (20 psi). For trans, trans-2,4-hexadiene the only product obtained when D₂ is used is 2,5-dideuterio-cis-3-hexene. The catalytic 1,4-hydrogenation can be carried out in neat dienes, and turnover numbers for the catalyst of greater than 3000 have been observed.     

Chemoselective Borane‐Catalyzed Hydroarylation of 1,3‐Dienes with Phenols

A B(C₆F₅)₃‐catalyzed hydroarylation of a series of 1,3‐dienes with various phenols has been established through a combination of theoretical and experimental investigations, affording structurally diverse ortho‐allyl phenols. DFT calculations show that the reaction proceeds through a borane‐promoted protonation/Friedel–Crafts pathway involving a π‐complex of a carbocation–anion contact ion pair. This protocol features simple and mild reaction conditions, broad functional‐group tolerance, and low catalyst loading. The obtained ortho‐allyl phenols could be further converted into flavan derivatives using B(C₆F₅)₃ with good cis diastereoselectivity. Furthermore, this transformation was applied in the late‐stage modification of pharmaceutical compounds.     

The mass spectra of isomeric hydrocarbons—II: The C5H8S isomers,spiropentane, cyclopentene, 1,3-pentadiene and isoprene; The mechanisms and energetics of their fragmentations

The mass spectra of spiropentane, cyclopentene, 1,3-pentadiene (piperylene), isoprene and some deuterium labelled analogues have been studied. The heats of formation of the molecular ions and the major daughter ions [C₅H₇]⁺ and [C₄H₅]⁺ have been estimated. Fragmentation of these molecules mostly proceeds via common intermediates in which hydrogen atoms have lost their positional identity. Only spiropentane displays any specific fragmentation behaviour related to its ground state geometry.