Metallbindungsphänomene: Alkoholat-Aggregate als unmittelbare Teilnehmer an Eliminierungsreaktionen

In solvents of low polarity it is neither a monomolecular nor a dissociated alcoholal species which effects dehydrohalogenation of vic-dihaloalkanes and vic-dihalocycloalkanes but rather a dimeric, trimeric or tetrameric alcoholate aggregate. This behavior has important implications for the stereochemical outcome of such elimination reactions.     

Chemistry of Benzocyclopropenes. 1H-and 13C-NMR. Spectra of 2, 5-dideuterio-1-fluorobenzocyclopropenium ion

Preparation of 1, 1-difluorobenzocyclopropene (4) and of its 2, 5- and 3, 4-dideuterio derivatives 4a and 4b is reported. Upon ionization in cold fluorosulfonic acid, 4 affords 1-fluorobenzocyclopropenium ion (6) . ¹H- and ¹³C-NMR. spectra of 4 and 6 are assigned on the basis of the data for the specifically deuteriumlabelled compounds 4a and 6a . Hydrolysis of 6a leads to 2, 5-dideuteriobenzoic acid (7a) .     

Influence of a diene impurity on the molecular structure of phosphate-containing polymers with medical applications

We have demonstrated that the unacknowledged presence of almost 30% diene impurity in some commercial phosphate monomers had not only a significant effect on the molecular structure (topology) of a series of synthesized polymers but the instability of the ester functionalities during these polymerizations resulted in unexpectedly complex co-polymer chemistry.     

Synthesis of four‐arm star poly(L‐lactide) oligomers using an in situ‐generated calcium‐based initiator

Using an in situ‐generated calcium‐based initiating species derived from pentaerythritol, the bulk synthesis of well‐defined four‐arm star poly(L ‐lactide) oligomers has been studied in detail. The substitution of the traditional initiator, stannous octoate with calcium hydride allowed the synthesis of oligomers that had both low PDIs and a comparable number of polymeric arms (3.7–3.9) to oligomers of similar molecular weight. Investigations into the degree of control observed during the course of the polymerization found that the insolubility of pentaerythritol in molten L ‐lactide resulted in an uncontrolled polymerization only when the feed mole ratio of L ‐lactide to pentaerythritol was 13. At feed ratios of 40 and greater, a pseudoliving polymerization was observed. As part of this study, in situ FT‐Raman spectroscopy was demonstrated to be a suitable method to monitor the kinetics of the ring‐opening polymerization of lactide. The advantages of using this technique rather than FTIR‐ATR and ¹H NMR for monitoring L ‐lactide consumption during polymerization are discussed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4736–4748, 2009     

2-Ethynylindene by rearrangement of 2-vinylidene-2H-indene and 2-indenylvinylidene

2-Ethynylidene is obtained by flash vacuum pyrolysis of naphtho[b] cyclopropene and 4-(2-indenylmethylidene)-3-methylisoxazol-5-(4$\text{H}$)-one.     

Natural history specimen analysis using micro FT-IR attenuated total reflectance spectroscopy and transmission electron microscopy

A combination of micro Fourier transform infrared (FT-IR) attenuated total reflectance (ATR) spectroscopy and transmission electron microscopy (TEM) provided a complete analysis of the interaction between nematode cuticle structure and preservation fluids. Spectroscopic results were successfully correlated with TEM results. While fresh nematode cuticle yielded uniform spectra, damaged cuticles were characterised by large spectrum to spectrum variations in the 1000-1100 cm-1 region. An important outcome of this investigation was the demonstrated potential of micro FT-IR ATR as a technique for the analysis of challenging natural history samples.     

Adsorption of well-defined fluorine-containing polymers onto poly(tetrafluoroethylene)

Adsorption of well-defined fluorinated polymers onto clinically relevant poly(tetrafluoroethylene) (PTFE) substrates offers an attractive method for modifying the surface properties of chemically inert PTFE. Reversible addition-fragmentation chain transfer (RAFT) was successfully used for synthesis of the polymers in this study: the homopolymers poly(2,3,4,5,6-pentafluorostyrene) (PFS), poly(2,2,3,3-tetrafluoropropyl acrylate) (PTFPA), and poly(2,2,3,3-tetrafluoropropyl methacrylate) (PTFPMA) as well as their block copolymers with tert-butyl acrylate ( (t)BA). Water-soluble blocks were synthesized through the hydrolysis of the t-butyl side groups of P( (t)BA) to the corresponding carboxylic acid. Adsorption of selected polymers onto PTFE from a series of solvents (methyl ethyl ketone (MEK), dimethylformamide (DMF), fluorobenzene (FB), dichloromethane (DCM)) was investigated using X-ray photoelectron spectroscopy (XPS) and sessile water drop measurements. The three homopolymers studied all adsorbed irreversibly (i.e., were not removed by washing) from organic solvents at ambient temperature. PFS displayed the highest adsorption, and was attributed to strong hydrophobic interactions. From angle-resolved XPS it was concluded that PFS became impregnated into the PTFE substrate down to depths of 100 A when using FB as a solvent. The carboxylic acid-containing block copolymers adsorbed more effectively from DMF (a good solvent for the poly(acrylic acid) block) compared to MEK. The resulting modified PTFE substrates displayed high stability with respect to desorption in aqueous solution, yet conformational changes of the adsorbed polymer resulted in a switchable hydrophobic-hydrophilic surface (in air or water, respectively). These results highlight the success of a facile and simple approach to irreversibly adsorb functional polymers to a nonfunctional fluorinated surface.     

Equivalency of the carbon atoms in the molecular ion of cyclopropabenzene

The carbon atoms of the molecular and [M? H]⁺ ions of cyclopropabenzene which are formed upon electron impact at 70 and at 12 eV lose their positional identity completely before C₂H₂ is expelled.