On the Effect of Tether Composition on cis/trans Selectivity in Intramolecular Diels–Alder Reactions

Intramolecular Diels–Alder (IMDA) transition structures (TSs) and energies have been computed at the B3LYP/6‐31+G(d) and CBS‐QB3 levels of theory for a series of 1,3,8‐nonatrienes, H₂C?CH? CH?CH? CH₂? X? Z? CH?CH₂ [? X? Z? =? CH₂? CH₂? ( 1 ); ? O? C(?O)? ( 2 ); ? CH₂? C(?O)? ( 3 ); ? O? CH₂? ( 4 ); ? NH? C(?O)? ( 5 ); ? S? C(?O)? ( 6 ); ? O? C(?S)? ( 7 ); ? NH? C(?S)? ( 8 ); ? S? C(?S)? ( 9 )]. For each system studied ( 1 – 9 ), cis‐ and trans‐TS isomers, corresponding, respectively, to endo‐ and exo‐positioning of the ? C? X? Z? tether with respect to the diene, have been located and their relative energies (E_rel^TS) employed to predict the cis/trans IMDA product ratio. Although the E_rel^TS values are modest (typically <3 kJ mol^?1), they follow a clear and systematic trend. Specifically, as the electronegativity of the tether group X is reduced (X?O→NH or S), the IMDA cis stereoselectivity diminishes. The predicted stereochemical reaction preferences are explained in terms of two opposing effects operating in the cis‐TS, namely (1) unfavorable torsional (eclipsing) strain about the C4? C5 bond, that is caused by the ? C? X? C(?Y)? group’s strong tendency to maintain local planarity; and (2) attractive electrostatic and secondary orbital interactions between the endo‐(thio)carbonyl group, C?Y, and the diene. The former interaction predominates when X is weakly electronegative (X?N, S), while the latter is dominant when X is more strongly electronegative (X?O), or a methylene group (X?CH₂) which increases tether flexibility. These predictions hold up to experimental scrutiny, with synthetic IMDA reactions of 1 , 2 , 3 , and 4 (published work) and 5 , 6 , and 8 (this work) delivering ratios close to those calculated. The reactions of thiolacrylate 5 and thioamide 8 represent the first examples of IMDA reactions with tethers of these types. Our results point to strategies for designing tethers, which lead to improved cis/trans‐selectivities in IMDAs that are normally only weakly selective. Experimental verification of the validity of this claim comes in the form of fumaramide 14 , which undergoes a more trans‐selective IMDA reaction than the corresponding ester tethered precursor 13 .     

Reactivity in the gas phase. Behaviour of isoxazoles under negative ion chemical ionization conditions

[M ? H⁺]^? ions of isoxazole (la), 3-methylisoxazole (1b), 5-methylisoxazole (1c), 5-phenylisoxazole (1d) and benzoylacetonitrile (2a) are generated using NICI/OH^? or NICI/NH₂^? techniques. Their fragmentation pathways are rationalized on the basis of collision-induced dissociation and mass-analysed ion kinetic energy spectra and by deuterium labelling studies. 5-Substituted isoxazoles 1c and 1d, after selective deprotonation at position 3, mainly undergo N ? O bond cleavage to the stable α-cyanoenolate NC ? CH ? CR ? O^? (R = Me, Ph) that fragments by loss of R? CN, or R? H, or H₂O. The same α-cyanoenolate anion (R = Ph) is obtained from 2a with OH^?, or NH₂^?, confirming the structure assigned to the [M ? H⁺]^? ion of 1d, On the contrary, 1b is deprotonated mainly at position 5 leading, via N? O and C(3)? C(4) bond cleavages, to H? C ≡ C? O ^? and CH₃CN. Isoxazole (1a) undergoes deprotonation at either position and subsequent fragmentations. Deuterium labelling revealed an extensive exchange between the hydrogen atoms in the ortho position of the phenyl group and the deuterium atom in the α-cyanenolate NC ? CD = CPh ? O^?.     

The [CH5NO]+ ˙ potential energy surface: Distonic ions,lon-dipole complexes and hydrogen-bridged radical cations

By combining results from a variety of mass spectrometric techniques (metastable ion, collisional activation, collision-induced dissociative ionization, neutralization-reionization spectrometry, ²H, ¹³C and ¹⁸O isotopic labelling and appearance energy measurements) and high-level ab initio molecular orbital calculations, the potential energy surface of the [CH₅NO]^{+ ˙} system has been explored. The calculations show that at least nine stable isomers exist. These include the conventional species [CH₃ONH₂]^{+ ˙} and [HO? CH₂? NH₂]^{+ ˙}, the distonic ions [O? CH₂? NH₃]^{+ ˙}, [O? NH₂? CH₃]^{+ ˙}, [CH₂? O(H)? NH₂]^{+ ˙}, [HO? NH₂? CH₂]^{+ ˙}, and the ion-dipole complex CH₂?NH₂⁺ …? OH˙. Surprisingly the distonic ion [CH₂? O? NH₃]^{+ ˙} was found not to be a stable species but to dissociate spontaneously to CH₂?O + NH₃^{+ ˙}. The most stable isomer is the hydrogen-bridged radical cation [H? C?O …? H …? NH₃]^{+ ˙} which is best viewed as an immonium cation interacting with the formyl dipole. The related species [CH₂?O …? H …? NH₂]^{+ ˙}, in which an ammonium radical cation interacts with the formaldehyde dipole is also a very stable ion. It is generated by loss of CO from ionized methyl carbamate, H₂N? C(?O)? OCH₃ and the proposed mechanism involves a 1,4-H shift followed by intramolecular ‘dictation’ and CO extrusion. The [CH₂?O …? H …? NH₂]^{+ ˙} product ions fragment exothermically, but via a barrier, to NH₄^{+ ˙} HCO^…? and to H₃N? C(H)?O^{+ ˙} H˙. Metastable ions [CH₃ONH₂]^+…? dissociate, via a large barrier, to CH₂?O + NH₃⁺ + and to [CH₂NH₂]⁺ + OH˙ but not to CH₂?O^{+ ˙} + NH₃. The former reaction proceeds via a 1,3-H shift after which dissociation takes place immediately. Loss of OH˙ proceeds formally via a 1,2-CH₃ shift to produce excited [O? NH₂? CH₃]^{+ ˙}, which rearranges to excited [HO? NH₂? CH₂]^{+ ˙} via a 1,3-H shift after which dissociation follows.     

Activation and racemization of trifluoroacetate esters in the cationic polymerization of styrene

1-Phenylethyl trifluoroacetate ( 1 ) does not react directly with styrene but it is readily incorporated into polymer chains in the presence of an excess of trifluoroacetic acid. The proportion of the nondeuterated 1-phenylethyl end groups in the polymerization of deuterated styrene coinitiated with the acid was much higher than the proportion of the end groups formed by direct incorporation of the acidic protons ([CH₃? CHPh? CD₂? CDPh? …] > [HCD₂? CDPh? CH₂? CDPh? …]). The racemization of the optically active ester-(pseudo-first order rate constant at [HA]₀ = 0.79 mol/L at 20°C equals k^R = 1.7 × 10^?4 S^?1) is more rapid than the incorporation of the ester into polymer chains (k^E = 1.5 × 10^?4 mol^?1 Ls^?1, [M]₀ < 0.4 mol L^?1, i.e., k^R > k^E · [M]). These results and the complete loss of the optical activity in the final polymer indicate that the ester is activated by the acid but it is incorporated into polymer chain via ionic intermediates.     

Bis(trimethylsilyl)-hypophosphit und Alkoxycarbonylphosphonigsäure-bis(trimethylsilyl)ester als Schlüsselsubstanzen für die Synthese von Organophosphorverbindungen

Bis(trimethylsilyl)hypophosphite und Alkoxycarbonylphosphonous Acid Bis(trimethylsilyl) esters as Building Blocks in Organophosphorus Chemistry The oxidation of pure bis(trimethylsilyl)hypophosphite ( BTH ) with chalcogenides forming (Me₃SiO)₂P(X)H (X = O, S, Se, Te) is described as well as its reactions with alkylhalides RX (X = Cl, Br, I) and Cl? C(O)OR (R = Me, Et, Bzl). By reaction with oxygen, sulfur, and selenium the alkoxycarbonylphosphonous acid bis(trimethylsilyl)esters form RO? C(O)? P(X)(OSiMe₃)₂ (X = O, S, Se) whereas with Cl? C(O)OR the bis(alkoxycarbonyl)-phosphinic acid trimethylsilylesters are obtained. After partial hydrolysis the resulting instable RO? C(O)? P(O)H(OSiMe₃) gives RO? C(O)? P(O)(OSiMe₃)? CH₂? NH? A? COOR′ (A = CH₂, CH₂CH₂, CHCH₃, CH₂CH₂SH, CHCH(CH₃)₂,…) when allowed to react with hexahydro-s-triazines of the aminoacid esters. Reactions of the alkoxycarbonyl-P-silylesters with NaOR or NaOH result in the corresponding mono-, di-, or trisodium salts. With mineral acids decarboxylation occurs, but H? P(O)(OH)? CH₂? NH? A? COOH can be obtained, too. The structure of the compounds described are discussed by their n.m.r. data.     

Loss of methyl from [H2CC(OH)?CH3]+˙ ions prepared by electron impact ionization of unstable 2-hydroxypropene

Unstable 2-hydroxpropene was prepared by retro-Diels-Alder decomposition of 5-exo-methyl-5-norbornenol at 800°C/2 × 10^?6 Torr. The ionization energy of 2-hydroxypropene was measured as 8.67±0.05 eV. Formation of [C₂H₃O]⁺ and [CH₃]⁺ ions originating from different parts of the parent ion was examined by means of ¹³C and deuterium labelling. Threshold-energy [H₂C?C(OH)? CH₃]^+˙ ions decompose to CH₃CO⁺+CH₃^˙ with appearance energy AE(CH₃CO⁺) = 11.03 ± 0.03 eV. Higher energy ions also form CH₂?C?OH⁺ + CH₃ with appearance energy AE(CH₂?C?OH⁺) = 12.2–12.3 eV. The fragmentation competes with hydrogen migration between C(1) and C(3) in the parent ion. [C₂H₃O]⁺ ions containing the original methyl group and [CH₃]⁺ ions incorporating the former methylene and the hydroxyl hydrogen atom are formed preferentially, compared with their corresponding counterparts. This behaviour is due to rate-determining isomerization [H₂C?C(OH)? CH₃]^+˙ →[CH₃COCH₃]^+˙, followed by asymmetrical fragmentation of the latter ions. Effects of internal energy and isotope substitution are discussed.     

Novel Copolymers of Alkyl and Alkoxy Ring‐Substituted Ethyl 2‐Cyano‐3‐phenyl‐2‐propenoates and Styrene

Abstract

Electrophilic trisubstituted ethylenes, ring‐substituted ethyl 2‐cyano‐3‐phenyl‐2‐propenoates, RC₆H₄CH?C(CN)CO₂C₂H₅ (where R is 2‐CH₃, 3‐CH₃, 4‐CH₃, 2‐OCH₃, 3‐OCH₃, and 4‐OCH₃) were prepared and copolymerized with styrene (ST). The monomers were synthesized by the piperidine catalyzed Knoevenagel condensation of ring‐substituted benzaldehydes and ethyl cyanoacetate, and characterized by CHN analysis, IR, ¹H and ¹³C NMR. All the ethylenes were copolymerized with ST (M₁) in solution with radical initiation (AIBN) at 70°C. The compositions of the copolymers were calculated from nitrogen analysis and the structures were analyzed by IR, ¹H and ¹³C NMR. The order of relative reactivity (1/r ₁) for the monomers is 3‐OCH₃ (0.88)?>?4‐CH₃ (0.71)?>?2‐OCH₃ (0.68)?>?3‐CH₃ (0.55)?>?2‐CH₃ (0.47)?>?4‐OCH₃ (0.40). Higher T _g of the copolymers in comparison with that of polystyrene indicates a decrease in chain mobility of the copolymer due to the high dipolar character of the TSE structural unit. Gravimetric analysis indicated that the copolymers decompose in the 257–287°C range.     

Carbanion rearrangements. Collison induced dissociations of deprotonated alkyl acetoacetates

Deprotonation of methyl acetoacetate yields two enolate ions MeCOC?HCO₂Me (a) and C?H₂COCH₂CO₂Me (b). On collisional activation, ions a and b fragment differently. The major fragmentation of a is specific loss of MeOH through a four-centred transition state to form ^?O(Me)C?C?C?O. In contrast, ion b eliminates CH₂CO to give ^?CH₂CO₂Me. Some rearrangement of b to a is also noted. Rearrangement of a to b is very minor under single collision conditions but at high collision gas pressure rearrangement of a to b is strongly promoted. Similar effects are observed in the collisional activation spectra of MeCOC?(Me)CO₂Me (c) and ^?CH₂COC(Me)CO₂Me (d). The loss of MeOH from (c) proceeds via a six membered transition state to ^?CH₂? CO? C(Me)?C?O; this is a stepwise process in which the deprotonation (step two) is not rate determining. A number of other decompositions occur, these have also been studied by deuterium labelling.     

Umsetzungen des Tetrakis[bis(trimethylsilyl)methyl]dialans(4) mit Methylisothiocyanat und Phenylisocyanat – Insertion in die Al?Al-Bindung bzw. Fragmentierung

Reactions of Tetrakis[bis(trimethylsilyl)methyl]dialane(4) with Methylisothiocyanate and Phenylisocyanate – Insertion into the Al? Al Bond and Fragmentation Tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 reacts with methyl isothiocyanate under cleavage of the C?S double bond and insertion of the remaining isonitrile fragment into the Al? Al bond. As shown by crystal structure determination a three-membered AlCN heterocycle ( 4 ) is formed by the interaction of the nitrogen lone pair with one unsaturated Al atom leading to an acute angle at the aluminium center N? Al? C of 36.6°. In contrast the reaction with the hard base phenyl isocyanate yields a mixture of many unknown compounds, from which only one ( 5 ) could be isolated in a very poor yield. The crystal structure of 5 reveals only one dialkyl aluminium fragment and a chelating ligand formed by the trimerization of the isocyanate under loss of one CO group and addition of a hydrogen atom. 5 was also synthesized by the specific reaction of the chloro dialkyl aluminium compound (R = CH(SiMe₃)₂) with Li[H₅C₆? N?C(O)? N(C₆H₅)? C(O)? N(H)? C₆H₅].     

The unimolecular chemistry of [1,2-propanediol]+˙: a rationale in terms of hydrogen-bridged radical cations

By combining results from a variety of mass spectrometric techniques (metastatle ion, collisional activation, collision-induced dissociative ionization, neutralization–reionization spectrometry and appearance energy measurements) and the classical method of isotopic labelling, a unified mechanism is proposed for the complex unimolecular chemistry of ionized 1,2-propanediol. The key intermediates involved are the stable hydrogen-bridged radical cations [CH₂?C(H)? H…?O…?O(H)CH₃]⁺˙, which were generated independently from [4-methoxy, 1-butanol]⁺˙ (loss of C₂H₄) and [1-methoxyglycerol]⁺˙ (loss of CH₂O), [CH₃? C?O…?H…?O(H)CH₃]⁺˙ and the related ion-dipole complex [CH₂?C(OH)CH₃/H₂O]⁺˙. The latter species serves as the precursor for the loss of CH³˙ and in this reaction the same non-ergodic behaviour is observed as in the loss of CH³˙ from the ionized enol of acetone.     

Loss of methyl from ionized 2-hydroxy-1,3-butadiene

The loss of methyl from unstable, metastable and collisionally activated [CH₂?CH? C(OH)?CH₂]⁺˙ ions (1⁺˙) was examined by means of deuterium and ¹³C labelling, appearance energy measurements and product identification. High-energy, short-lived 1⁺˙ lose methyl groups incorporating the original enolic methene (C(1)) and the hydroxyl hydrogen atom (H(0)). The eliminations of C(1)H(1)H(1)H(4) and C(4)H(4)H(4)H(0) are less frequent in high-energy ions. Metastable 1⁺˙ eliminate mainly C(1)H(1)H(1)H(4), the elimination being accompanied by incomplete randomization of the five carbon-bound hydrogen atoms. The resulting [C₃H₃O]⁺ ions have been identified as the most stable CH₂?CH? CO⁺ species. The appearance energy for the loss of methyl from 1 was measured as AE[C₃H₃O]⁺ = 10.47 ± 0.05 eV. The critical energy for 1⁺˙ → [C₃H₃O]⁺ + CH₃˙ is assessed as E_c ? 173 kJ mol^?1. Reaction mechanisms are proposed and discussed.     

Substituted propenyl end groups as reactive intermediates in radical polymerization

The addition of propagating radicals of methyl acrylate (MA) and styrene (St) to CH₂?C(CO₂CH₃)CH₂? and CH₂?C(C₆H₅)CH₂? ω‐end groups of poly(methyl methacrylate) (PMMA) and polystyrene (PSt) was investigated. The end groups were as reactive as MA and St toward the poly(methyl acrylate) (PMA) and PSt radicals, respectively. The adduct radical derived from the two types of PMMA end groups and PMA radicals underwent β fragmentation exclusively to yield PMMA radicals and end groups bound to PMA chains. The addition of PSt radicals to PMMA with CH₂?C(CO₂Me)CH₂? end groups resulted in adduct radicals that underwent β fragmentation and addition to St or coupling with PSt radicals. Adduct radicals formed by the addition of PMA radicals to both types of end groups of PSt exclusively formed C? C bond by coupling with PMA radicals to form branched structures or by addition to MA monomer to give a copolymer. The fate of the adduct radicals was highly dependent on the type of polymer chain and the substituent bound to the end group. Steric congestion of the adduct radical arising from the α‐methyl group of the PMMA chain was considered to be crucial for fragmentation to expel the PMMA radical. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 645–654, 2003     

Crystal structure of a liquid crystal non‐symmetric dimer: cholesteryl 4‐[4‐(4‐n‐butylphenylethynyl)phenoxy]butanoate

The crystal structure of cholesteryl 4‐[4‐(4‐n‐butylphenylethynyl)phenoxy]butanoate [phase sequence: Cr 155°C (46.1?J?g^?1) SmA 186.8°C (1.5?J?g^?1) TGB‐N* 204.7 (6?J?g^?1) I] has been solved from single crystal X‐ray diffraction data. The compound crystallizes in the monoclinic space group P2₁ with unit cell parameters: a?=?13.129(2), b?=?9.3904(10), c?=?17.4121(8)?Å, β?=?92.790(7)°, Z?=?2. The structure has been solved by direct methods and refined to R?=?0.0606 for 3?250 observed reflections. The bond distances and angles are in good agreement with the corresponding values for compounds containing phenyl and cholesterol moieties. The phenyl rings A and B are planar. The dihedral angle between the least‐squares planes of the two phenyl rings is 28°. The cholesterol moiety has the usual structure: the C and E rings have chair conformations, and the D and F rings adopt half‐chair conformations. The molecules in the unit cell are arranged in an antiparallel manner. The crystal structure is stabilized by an intermolecular C–H…O contact of 2.989(10)?Å.     

Untersuchungen über das Reaktionsverhalten von Antimonpentachlorid. III [1]. Zur Reaktion von Antimon (V)-chlorid mit Methylisocyanat

Studies on the Reactivity of Antimony Pentachloride. III. The Reaction of Antimony(V) Chloride and Methylisocyanate Methylisocyanate CH₃NCO reacts with SbCl₅ in boiling CCl₄ by an insertion-reaction to a product of the formula C₅H₆Cl₉N₂O₂Sb I, which has the chlorformamidinium-structure (Cl? C(O)? N(CH₃)? CCl? N(CH₃)? C(O)? Cl)⊕SbCl₆?. Hydrolysis of I yields the heterocycle C₅H₆N₂O₄ II. The reaction with methanol gives (CH₃? NH? CCl? NH? CH₃)⊕SbCl₆? III and (CH₃? NH? CCl? N(CH₃)? C(O)? OCH₃)⊕SbCl₆? IV. The i.r. and Raman spectra of the compounds I, III and IV are discussed.     

Rearrangements in Model Peptide‐Type Radicals via Intramolecular Hydrogen‐Atom Transfer

Intramolecular H‐atom transfer in model peptide‐type radicals was investigated with high‐level quantum‐chemistry calculations. Examination of 1,2‐, 1,3‐, 1,5‐, and 1,6[C ? N]‐H shifts, 1,4‐ and 1,7[C ? C]‐H shifts, and 1,4[N ? N]‐H shifts (Scheme 1), was carried out with a number of theoretical methods. In the first place, the performance of UB3‐LYP (with the 6‐31G(d), 6‐31G(2df,p), and 6‐311+G(d,p) basis sets) and UMP2 (with the 6‐31G(d) basis set) was assessed for the determination of radical geometries. We found that there is only a small basis‐set dependence for the UB3‐LYP structures, and geometries optimized with UB3‐LYP/6‐31G(d) are generally sufficient for use in conjunction with high‐level composite methods in the determination of improved H‐transfer thermochemistry. Methods assessed in this regard include the high‐level composite methods, G3(MP2)‐RAD, CBS‐QB3, and G3//B3‐LYP, as well as the density‐functional methods B3‐LYP, MPWB1K, and BMK in association with the 6‐31+G(d,p) and 6‐311++G(3df,3pd) basis sets. The high‐level methods give results that are close to one another, while the recently developed functionals MPWB1K and BMK provide cost‐effective alternatives. For the systems considered, the transformation of an N‐centered radical to a C‐centered radical is always exothermic (by 25 kJ ? mol^?1 or more), and this can lead to quite modest barrier heights of less than 60 kJ ? mol^?1 (specifically for 1,5[C ? N]‐H and 1,6[C ? N]‐H shifts). H‐Migration barriers appear to decrease as the ring size in the transition structure (TS) increases, with a lowering of the barrier being found, for example when moving from a rearrangement proceeding via a four‐membered‐ring TS (e.g., the 1,3[C ? N]‐H shift, CH₃? C(O)? NH^. → ^.CH₂? C(O)? NH₂) to a rearrangement proceeding via a six‐membered‐ring TS (e.g., the 1,5[C ? N]‐H shift, ^.NH? CH₂? C(O)? NH? CH₃ → NH₂? CH₂? C(O)? NH? CH₂^.).     

UHMWPE with short‐chain branches synthesized by alkenyl substituted phenoxy–imine catalysts in ethylene polymerization

The alkenyl substituted phenoxy–imine complexes [2‐C₃H₅‐6‐(2, 3, 5, 6‐C₆F₄H‐N?CH)C₆H₃O]₂TiCl₂ (C₃H₅=? CH₂? CH?CH₂ or ? CH?CH? CH₃) are synthesized and characterized by ¹H NMR, ¹³C NMR, and elemental analysis. When activated by MAO, they show high activity for the polymerization of ethylene to UHMWPE under different conditions (temperatures and polymerization time). Most of the resulting polymers have high molecular weights (>1.0 × 10⁶ g·mol^?1) and high melting points as well as crystallinity. To clarify the effect of the alkenyl group on the catalytic performance and the resultant polymer microstructure, the corresponding saturated complexes of type [2‐C₃H₇?6‐(2, 3, 5, 6‐C₆F₄H‐N?CH)C₆H₃O]₂TiCl₂ where C₃H₇ = –CH₂? CH₂? CH₃ or ? CH(CH₃)₂ were synthesized and tested as catalysts in ethylene polymerization under the same reaction conditions. The microstructure and morphologies of these two species of PE samples were fully compared by the analysis of ¹³C NMR, GPC, DSC, and SEM. As a result, the allyl substituted complex show the highest activity to prepare the highest molecular weight polyethylene of all the catalysts. An interesting feature of the UHMWPE produced by these four catalysts is that they contain only a few short‐chain branches (mainly methyl, isobutyl and 2‐methylhexyl branches) in a low amount (<2.7 branches/1000 C). © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3808–3818     

Characterization of five [C4H7O]+ Ion structures. Fragmentation of the 2-pentanone molecular ion

The [C₄H₇0]⁺ ions [CH₂?CH? C(?OH)CH₃]⁺ (1), [CH₃CH?CH? C(?OH)H]⁺ (2), [CH₂?C(CH₃)C(?OH)H]⁺ (3), [Ch₃CH₂CH₂C?O]⁺ (4) and [(CH₃)₂CHC?O]⁺ (5) have been characterized by their collision-induced dissociation (CID) mass spectra and charge stripping mass spectra. The ions 1–3 were prepared by gas phase protonation of the relevant carbonyl compounds while 4 and 5 were prepared by dissociative electron impact ionization of the appropriate carbonyl compounds. Only 2 and 3 give similar spectra and are difficult to distinguish from each other; the remaining ions can be readily characterized by either their CID mass spectra or their charge stripping mass spectra. The 2-pentanone molecular ion fragments by loss of the C(1) methyl and the C(5) methyl in the ratio 60:40 for metastable ions; at higher internal energies loss of the C(1) methyl becomes more favoured. Metastable ion characteristics, CID mass spectra and charge stripping mass spectra all show that loss of the C(1) methyl leads to formation of the acyl ion 4, while loss of the C(5) methyl leads to formation of protonated vinyl methyl ketone (1). These results are in agreement with the previously proposed potential energy diagram for the [C₅H₁₀O]⁺˙ system.     

Tetrakis(chloromethyl)phosphonium chloride monohydrate

Tetrakis­(chloro­methyl)­phospho­nium chloride monohydrate, C₄H₈Cl₄P⁺·Cl^?·H₂O or P(CH₂Cl)₄⁺·Cl^?·H₂O, is the first crystal structure determination of a tetrakis­(halogeno­methyl)­phospho­nium compound to date. The only comparable structures known so far are of phospho­nium ions containing just one halogeno­methyl group. The solvent water mol­ecule interacts with the Cl^? anion via hydrogen bonds, with O?Cl distances of 3.230 (2) and 3.309 (2) Å. The structure also contains several C—H?Cl^? and C—H?O contacts, though with longer D?A distances [D?A 3.286 (3)–3.662 (2) Å] or bent D—H?A angles. For these reasons, the C—H?Cl^? and C—H?O interactions should not be considered as strong hydrogen bonds.     

Characterization of the ladder polymerization of a crystalline cyclotetradiyne monomer

The polymerization of the cyclic tetradiyne monomer, [? (CH₂) ₂? C?C? C?C? (CH₂)₂? ]₄, containing interstitial chloroform has been investigated using Raman and Fourier-transform infrared spectroscopy and x-ray diffraction techniques. A loss of crystallographic register between chains occurs during the polymerization reaction, although crystalline order in the chain-axis projection is retained. These studies indicate that 50 Mrad of ⁶⁰Co γ-ray irradiation produces 1,4-addition polymerization at most of the diacetylene functionalities. Unreacted diacetylene groups are present primarily, although not completely, in soluble oligomeric material. Infrared spectroscopy indicates that this low molecular weight material has a butatriene (cumulene) backbone structure rather than the acetylenic structure of the insoluble polymer.     

Reaktionen von Undecacarbonyl(acetonitril)trieisen mit Alkinethern

Reactions of Undecacarbonyl(acetonitrile)triiron with Alkyne Ethers (CO)₁₁(CH₃CN) 1 reacts with the alkyne ethers H₃C? C?C? OC₂H₅ 2a , H? C?C? OC₂H₅ 2b , H₃C? O? CH₂? C?C? CH₂? O? CH₃, 2c and H₃C? O? C(CH₃)H? C?C? C(CH₃)H? O? CH₃ 2d forming different cluster products depending on the substituents and the reaction conditions. The product obtained with 2a is the bisalkylidyne cluster Fe₃(CO)₉(m?₃-C? CH₃)(m?₃-C? OC₂H₅) 3 which results from the cleavage of the carbon carbon triple bond. The alkyne 2b however yields the vinylidene cluster Fe₃(CO)₁₀(m?₃-η²-C? C(H)OC₂H₅) 4 by 1,2 proton shift. The alkyne clusters Fe₃(CO)₁₀(m?₃-η²-C? C(H)OC₂H₅) 4 by 1,2 proton shift. The alkyne clusters Fe₃(CO)₁₀(m?₃-η²- H₃ C? O? CH₂? C?C? CH₂? O? CH₃) 6 and Fe₃(CO)₉(m?-η²-H₃C? O? CH₂? C?C? CH₂? O? CH₃) 7 are the isolated products obtained from 2c . Thermolysis of 7 results in the formation of the dinuclear butatrien complex Fe₂(CO)₆ (H₂C? C? C? CH₂) 8a . The analogous compound Fe₂(CO)₆[H(H₃C)C ? C ? C ? C(CH₃)H] 8b is the only product of 2d and 1 . The structures of 4, 5 , and 6 have been determined by crystal structure determinations.