Mass spectrometry of organic compounds X–Fragementation of 2-buten-1-o1 on electron-impact

The mass spectra of variously deuterated 2-buten-1-ols (both Z and E) have been examined. Evidence is presented for the formation of the [M – H₂O]⁺· ion via a 6-membered transition state, and for the occurrence of two distinct reaction pathways for formation of the major ions at m/e 57 and 43.     

Enhanced stability to decomposition of a cobalt-dioxygen adduct supported in a copolymer matrix

Summary The decomposition of the Co^II complex of a macrocyclic cyclidene ligand is reported both in solution and when bound to a copolymer support. E.s.r. studies show that the decomposition of the complex in pyridine solution, under an atmosphere of O₂, has an estimated half-life of ca. 36 h at 295 K. This suggests that decomposition of the O₂ adduct is the second step observed in earlier electronic spectroscopic studies, and infers that the cyclidene O₂ adducts are much longer lived than originally thought. The Co^II cyclidene complex forms a coordinate bond to the pyridine group of n-butyl methacrylate/4-vinyl pyridine copolymers and the resulting five-coordinate complexes undergo reversible oxygenation. The polymer-supported O₂ adducts are much more stable to decomposition than those in the solution phase and have an estimated half-life of ca. 30 days at 295 K. The enhanced stability to decomposition of the complexes in the polymer matrix is attributed to the low mobility of the complexes in the glassy polymer.     

Is there a photochemical Hammond postulate?

The Hammond postulate is a useful tool for approximating the energy and the structure of transition states. It was designed for use in ground state reactions, and has been applied successfully on many occasions. On the other hand, its usefulness for photochemical reactions is more questionable, as different energy surfaces are involved. So far, no systematic studies on the validity of the Hammond postulate for photochemical reactions are available. The present work aims at filling this gap by providing a simple, unbiased series of test reactions based on the stereospecificity of isotopically labelled substrates.

In this work, a series of photochemical reactions were performed on isotopically labelled substrates to explore the validity of Hammond''s postulate for the excited state.     

Organometallic oligomers based on 1,8-Diisocyano-p-menthane (dmb): syntheses and characterization of the [[M(diphos)(dmb)]BF4]n and [[Pd2(diphos)2(dmb)](ClO4)2]n materials (M = Cu, Ag; diphos = dppe, dppp)

A new strategy to synthesize organometallic oligomers is presented and consists of using the title diisocyanide and chelated metal fragments with bis(diphenylphosphine)alkanes. The title materials are synthesized by reacting the [M(dppe)(BF4)] and [M2(dppp)2](BF4)2 complexes (M = Cu, Ag; dppe = bis(diphenylphosphino)ethane, dppp = bis(diphenylphosphino)propane) with dmb and the Pd2-bonded d9-d9 Pd2(dmb)2Cl2 dimer with dppe or dppp. The model compounds [M(diphos)(CN-t-Bu)2]BF4 (M = Cu, Ag) and [Pd2(diphos)2(CN-t-Bu)2](ClO4)2 (diphos = dppe, dppp) have been prepared and characterized as well for comparison purposes. Three of the model compounds were also characterized by X-ray crystallography to establish the diphosphine chelating behavior. The materials are amorphous and have been characterized from the measurements of the intrinsic viscosity, DSC, TGA, and XRD, as well as their capacity for making stand-alone films. The intrinsic viscosity data indicate that the Cu and Pd2 materials are oligomeric in solution (approximately 8-9 units), while the Ag materials are smaller. For [[Cu(dppe)(dmb)]BF4]n, a glass transition is reproducibly observed at about 82 degrees C (DeltaCp = 0.43 J/(g deg)), which suggests that these materials are polymeric in the solid state. The Cu and Ag species are luminescent in the solid state at room temperature exhibiting lambda(max) and tau(e) (emission lifetime) around 480-550 nm and 18-48 micros, respectively, while the Pd2 species are not luminescent under these conditions. During the course of this study, the unsaturated [M2(dppp)2](BF4)2 starting materials (M = Cu, Ag) were prepared, one of which (M = Ag) was characterized by crystallography. The bridging behavior of the dppp ligand in this case contrasts with the chelating behavior seen for the saturated [Cu(dppp)(CN-t-Bu)2]BF4 complex.     

The mass spectra of the trimethylsilyl esters of acetyl,schiff base and isothiocyanate derivatives of some aminoalkylphosphonic acids

Trimethylsilyl esters of acetyl, Schiff base and isothiocyanate derivatives of a series of aminoalkylphosphonic acids were prepared for the purpose of characterizing these phosphorus compounds by combined gas chromatography and mass spectrometry. The mass spectra of these derivatives were investigated by means of high resolution mass measurments and deuterium labeling. Ions characteristic of the presence of the trimethylsilylphosnate group were observed at m/e 121, 195, 211 and 225 to 227 in the spectra of all the derivatives. Several ions produced by interaction between the trimethylsilyl group and the derivatized amino function were present, particularly in the spectra of the acetate derivatives ([M — 56]⁺, [M — R]⁺ and [M — 153]⁺, where R is the side chain attached to C-1), and the isothiocynate derivatives (m/e 268, 253, 241, 190 and 116).     

Investigating the feasibility of mid infrared spectroscopy for monitoring an industrial de-racemization biotransformation process

Biotransformation processes have become industrially important in recent years as routes to the manufacture of high value chemical intermediates. However, measurements of key process features and analyte concentrations during these processes are still typically carried out using off-line analysis methods. Vibrational spectroscopic techniques have been extensively utilised for the monitoring and control of a variety of industrial processes. Despite the techniques success with a range of challenging biological matrices, including fermentation and cell culture systems, application of this approach to biotransformation systems has been limited. In the present study the potential of mid infrared spectroscopy to monitor an industrially relevant de-racemization biotransformation process has been investigated. This process presents a number of difficulties due to the optically challenging sample media, close structural similarities and stoichiometric relationship between the key analytes of interest. A PLS model based on the mid infrared spectra obtained during three replicates of the biotransformation process was constructed. In order to ensure that co-linearity within the system had been adequately addressed the spectral contributors to the model were examined. External validation of the constructed model was achieved by challenging the model with two previously unseen replicates of the process. The constructed model was able to predict the concentrations of two key analytes in various samples from these unseen replicates without the requirement for any time consuming sample pre-treatment stages, thus demonstrating the feasibility of near real-time mid infrared monitoring of such an industrial de-racemization biotransformation process.