Studies in nuclear magnetic resonance—XII: Complete analysis of the proton spectra of tert-butylcyohexane-3,3,4,4,5,5-d6 and -3,3,5,5-d4

Accurate parameters for the two title compounds have been obtained by the aid of a spectral subtraction technique in conjunction with analysis by LAOCN3. It is observed that J_{1eq, 6eq} and J_{1ax, 2ax} are abnormally large and small, respectively, and the significance of these and other coupling constants are discussed in terms of the probable geometry of tert-butylcyclohexane. The tert-butyl group affects the chemical shifts of the 4-protons, indicating that tert-butylcyclohexyl derivatives are poor models for fixed conformers of monosubstituted cyclohexanes. The deuterium isotope effects on proton chemical shifts appear to be influenced by the same factors as proton-proton coupling constants.     

Matrix screening of substituted N-aryl-1,8-naphthalimides reveals new dual fluorescent dyes and unusually bright pyridine derivatives

A 3 x 14 matrix of substituted N-aryl-1,8-naphthalimides was synthesized for the evaluation and discovery of dual fluorescence. Because of their unique photophysical properties, these dual fluorescent systems represent an exception to the widely studied TICT (Twisted Internal Charge Transfer) fluorescent dyes or tautomeric benzofluorescein class of two-color dyes. The matrix library was designed to investigate the effects of heterocycles, particularly pi-excessive and pi-deficient systems. Of the 42 compounds surveyed, five displayed well-resolved two-color emission in solvents as nonpolar as hexane. Based on the observed trends in fluorescence lambda(max) and quantum yield, a new model is proposed that predicts LW and SW emission for these systems. In addition, this model provides potential design features for the synthesis of new dual fluorescent species.     

Spectroscopic studies of Lewis acid-base complexes: Part V. Raman and infrared spectra,assignments and normal coordinate analysis for difluorophosphine borane

Raman spectra of five isotopic species of HPF₂BH₃ have been obtained in the liquid and solid states together with infrared spectra of the same species in the gaseous and solid states. Vibrational assignments have been made with the aid of a normal coordinate analysis utilizing compliance constants. Both compliance and force constants are reported. The force field is quite similar to that of PF₃BH₃ despite the marked difference in stability of the two compounds.     

The influence of spatial separation on divided listening

If spatial attention acts like a "spotlight," focusing on one location and excluding others, it may be advantageous to have all targets of interest within the same spatial region. This hypothesis was explored using a task where listeners reported keywords from two simultaneous talkers. In Experiment 1, the two talkers were placed symmetrically about the frontal midline with various angular separations. While there was a small performance improvement for moderate separations, the improvement decreased for larger separations. However, the dependency of the relative talker intensities on spatial configuration accounted for these effects. Experiment 2 tested whether spatial separation improved the intelligibility of each source, an effect that could counteract any degradation in performance as sources fell outside the spatial spotlight of attention. In this experiment, intelligibility of individual sources was equalized across configurations by adding masking noise. Under these conditions, the cost of divided listening (the drop in performance when reporting both messages compared to reporting just one) was smaller when the spatial separation was small. These results suggest that spatial separation enhances the intelligibility of individual sources in a competing pair but increases the cost associated with having to process both sources simultaneously, consistent with the attentional spotlight hypothesis.     

Synthesis of enantiopure allylamines by reductive alkylation of amino epoxides with organolithium reagents

[reaction: see text] Transformation of enantiopure (2R,1'S)-2-(1-aminoalkyl)epoxides 1 into the corresponding allylamines 2 is described. The opening of the epoxide ring with different organolithium compounds takes place with total selectivity and in high yields.     

On the Hörmander Classes of Bilinear Pseudodifferential Operators

Bilinear pseudodifferential operators with symbols in the bilinear analog of all the Hörmander classes are considered and the possibility of a symbolic calculus for the transposes of the operators in such classes is investigated. Precise results about which classes are closed under transposition and can be characterized in terms of asymptotic expansions are presented. This work extends the results for more limited classes studied before in the literature and, hence, allows the use of the symbolic calculus (when it exists) as an alternative way to recover the boundedness on products of Lebesgue spaces for the classes that yield operators with bilinear Calderón–Zygmund kernels. Some boundedness properties for other classes with estimates in the form of Leibniz’ rule are presented as well.     

The obrechkoff integral transform: properties and relation to a generalized fractional calculus

This survey is devoted to one of the most general Laplace-type integral transforms, the so-called Obrechkoff integral transform, introduced and studied for the first time by Obrechkoff[25]. It has been modified by Dimovski [5],[6] and used as a basis of a Mikusinski-type operational calculus for the hyper-Bessel differential operators of arbitrary order. Later, in a series of papers Dimovski and Kiryakova [8],[9],[10] have found operational properties, complex and real inversion formulas, Abel-type theorems for the Obrechkoff transform. This theory has been further developed by Kiryakova [16],[17],[18] using the tools of the Meijer's G-functions and of the fractional calculus. Namely, a new definition as a G-transform has been given for the Obrechkoff transform. The hyper-Bessel operators themselves, have given rise to a new generalized fractional calculus and further extensive use of the G-functions. Many other generalized differentiation and integration operators happen to be special cases in this calculus, too. Special cases of the Obrechkoff transform have been "rediscovered" later by many authors. We give examples how their results could be derived from the general ones surveyed here.     

Incompatible elements in bottom sediments of the Itaipú Dam Reservoir by EDXRF

Journal of Radioanalytical and Nuclear Chemistry - Sediments play an important role in the distribution of trace elements in the aquatic system and act as a sink for metals. Incompatible elements...     

Studies towards the synthesis of ertugliflozin from l-Arabinose

A new method for the diastereoselective synthesis of enantiomerically pure ertugliflozin was developed. The crucial step involves an aldol condensation between 1-(4-chloro-3-(4-ethoxybenzyl)phenyl)ethanone and (4R,5R)-5-(((tert-butyldimethylsilyl)oxy)methyl)-2,2-dimethyl-5-((trityloxy)methyl)-1,3-dioxolane-4-carbaldehyde, which was prepared from known 2-C-trityloxymethyl-2,3-O-isopropylidene-l-erythrose (easily accessible in three steps from l-arabinose) by standard reduction/oxidation and protection/deprotection manipulations. Dihydroxylation of the aldol condensation product and further global deprotection led to the formation of the target molecule.