Alkylation of picolinaldehyde with bromohydrins. A new class of heterocyclic ring tautomers

Entry into the pyrido[2, 1-c] [1,4]oxazinium and pyrido(2,1-c] [1,4]oxazepinium ring systems has been achieved by the interaction of picolinaldehyde with 2-bromoethanol and 3-bromo-propanol, respectively. The products, ring-tautomeric hemiacetals, are presumably formed by rapid hemiacetalization, followed by an intramolecular Menschutkin Reaction.     

The elimination of metal(I) hydride in the mass spectra of some metal(II) compounds

Metal(I) hydrides are eliminated as neutral species in the electron impact ionization mass spectra of copper(II) and palladium(II) complexes of ethylene-N,N′-3-benzoylprop-2-en-2-amine. Deuterium labelling shows that the hydrogen atom of the metal(I) hydride is derived predominantly from the ethylene bridge both for ion source reactions and for metastable ion transitions. Evidence supporting the proposed rationalization for elimination of metal(I) hydride is provided by the observation of an analogous reaction in the mass spectrum of (ethylene-N,N′-salicylaldiminato)copper(II). The mass spectrum of ethylene-d₄-N,N′-3-benzoylprop-2-en-2-amine shows an unusual rearrangement to give [C₇H₅D₂]⁺ ions involving a formal phenyl-to-methylene transfer.     

Characterization by three-dimensional representation of sequential transitions of metastable ions in a double focusing mass spectrometer

The ion currents due to products of selected ion reactions of toluene and 3-chlorophenol, occurring in the source or flight tube of a double focusing mass spectrometer for which the electric sector precedes the magnetic sector, have been represented by plotting them against two variables that reflect independently the effects of the sectors. The daughter ion produced from the molecular ion of 3-chlorophenol that decays by sequential losses of CO in the field free region preceding the electric sector and Cl˙ in the field free region preceding the magnetic sector gives rise to a peak with a distinctive shape on the resultant three-dimensional surface. A peak due to the daughter ion arising from the corresponding sequential losses of H˙ and C₂H₂ from the molecular ion of toluene could not be detected. A portion of the ion kinetic energy spectrum which would be recorded by a detector at the energy resolving slit is derived from the surface for 3-chlorophenol and is in satisfactory agreement with a published spectrum.     

Union of capillary high-performance liquid chromatography and microcoil nuclear magnetic resonance spectroscopy applied to the separation and identification of terpenoids

This paper describes the first coupling of a commercial capillary HPLC system with a diode array spectrophotometric detector and a custom-built nuclear magnetic resonance (NMR) flow microprobe. The eluent from a 3-microm diameter C18 HPLC column is linked to a 500 MHz 1H-NMR microcoil probe with an observe volume of 1.1 microl. The separation and structurally-rich detection of a mixture of terpenoids under both isocratic and gradient solvent elution conditions is presented. The lowest limits of detection yet reported for capillary HPLC on-line measurement (i.e., 37 ng for alpha-pinene) are achieved with this system. The complementary nature of diode array and NMR detection allows stopped-flow data collection from analytes which would otherwise go unnoticed in continuous-flow NMR. Moreover, stopped-flow NMR data is presented for the detection of a trace (sub-nmol) impurity in the sample mixture. Since NMR signals degrade and shift during solvent gradients, flow injection analysis studies are conducted with injected solvent plugs differing in mobile phase composition. The NMR signal degradation accompanying these injections is largely due to the variance in chemical shift with the solvent composition rather than to changes in magnetic susceptibility of the solvent. Characterization of such effects enables the development of improved NMR probes for the coupling of capillary HPLC and NMR.     

In-situ X-ray imaging of III-V strained-layer relaxation processes

The important value of the X-ray topography (XRT) technique for the investigation of III-V strained-layer relaxation processes is described. In addition to post-growth ex-situ XRT studies, a unique combined XRT/MBE growth facility has been constructed which allows the generation, motion and interaction of misfit dislocations to be monitored in-situ during epilayer growth, for the first time. The in-situ data already obtained for (100) InGaAs strained-layer growth on both Czochralski- and vertical-gradient freeze-grown GaAs substrates indicates technologically important differences in the initial relaxation process, including, in the latter case, the observation of a previously unreported secondary relaxation phase. Initial results relating to the influence of both post-growth annealing and the subsequent cool-down process are also described.     

Dipolar relaxations in the glass transition region and in the liquid crystalline phase of two side-chain liquid crystalline polysiloxanes

The molecular relaxation mechanisms in the glass transition region and in the liquid crystalline phase exhibited by two side-chain liquid crystalline polysiloxanes have been studied by Thermally Stimulated Discharge Currents. These results were compared with those previously obtained by dielectric relaxation spectroscopy. It was observed that two relaxation mechanisms were present in the liquid crystalline phase, and we suggest that these might correspond to the motions of the mesogenic moieties in the liquid crystalline phase. © 1996 John Wiley & Sons, Inc.     

The use of photoinitiated free-radical cyclopolymerization in the preparation of novel side-chain liquid-crystalline polydienes

The technique of photoinitiated free-radical cyclopolymerization has been used to produce a variety of novel side-chain liquid-crystalline (SCLC) polymers in which an alicyclic ring structure is incorporated into a polymer backbone. Most of the SCLC polymers gave glass transition temperatures (T_g) around room temperature and clearing points around 60–70°C. However, the poly(1,5-hexadiene) was the exception to this, exhibiting a T_g value of 14.5°C and a clearing point of 132.5°C. Confirmation of the structure of the alicyclic ring along the polymer backbone is extremely difficult to obtain, but evidence is given in the paper to support the ring structure.     

Crust density in bread baking: Mathematical modelling and numerical solutions

A model for the formation of a “crust” during bread baking is presented. The crust is the outermost part of the loaf where the final bread density is significantly higher than in the “crumb”, the interior of the loaf. The model is based on a collapse mechanism, whereby raised pressures due to thermal expansion and water evaporation squash bubbles in the bread as the dough sets and fractures; the latter process allows vapour within bubbles to escape.     

Directional tunneling escape from nearly spherical optical resonators

We report the surprising observation of directional tunneling escape from nearly spherical fused-silica optical resonators, in which most of the phase space is filled with nonchaotic regular trajectories. Experimental and theoretical studies of the dependence of the far-field emission pattern on both the degree of deformation and the excitation condition show that nonperturbative phase-space structures in the internal ray dynamics profoundly affect tunneling leakage of the whispering-gallery modes.     

On the Cash Balance Problem

The problem of determining the optimal level of a firm's cash balance has been studied by many researchers. Their analyses differ with respect to the assumptions made about both the cost structure faced by the firm and the nature of the flow of funds to the firm. Because of the different methodologies employed by these authors, a proof of the form of the optimum policy only exists for some assumptions about costs and cash flow conditions. Under other conditions, authors have simply assumed the form of the policy and solved for the parameters of that policy. This paper uses a general dynamic programming formulation of the cash balance problem to derive the form of the optimal cash balance problem under different assumptions about transaction costs and the demand for funds. It consists of a review, synthesis, generalization, and in many cases gives a more rigorous derivation of results. Also the nature of the cash balance problem is expanded in the interest of realism, to allow for access to short-term sources of funds.