A study of the possible and preferred site of protonation in 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene by vibrational spectroscopic methods

The normal co-ordinate analysis have been carried out for 7-methyl-1,5,7-triazabicyclo[4,4,0]dec-5-ene (MTBD) and its three possible protonated tautomeric forms. The calculations and measured infrared (IR) spectra are consistent with a tautomeric species in which the proton is attached to an imine nitrogen atom.     

An N-heterocyclic carbene/Lewis acid strategy for the stereoselective synthesis of spirooxindole lactones

A cooperative catalysis approach for the enantioselective formal [3+2] addition of α,β-unsaturated aldehydes to isatins has been developed. Homoenolate annulations of β-aryl enals catalyzed by an N-heterocyclic carbene (NHC) require the addition of lithium chloride for high levels of enantioselectivity. This NHC-catalyzed annulation has been used for the total synthesis of maremycin B.     

Robustness of fat quantification using chemical shift imaging

The purpose of this study was to investigate the effect of parameter changes that can potentially lead to unreliable measurements in fat quantification. Chemical shift imaging was performed using spoiled gradient echo sequences with systematic variations in the following: two-dimensional/three-dimensional sequence, number of echoes, delta echo time, fractional echo factor, slice thickness, repetition time, flip angle, bandwidth, matrix size, flow compensation and field strength. Results indicated no significant (or significant but small) changes in fat fraction with parameter. The significant changes can be attributed to the known effects of T1 bias and two forms of noise bias.     

Möbius characterization of hemispheres

In this paper we generalize the Möbius characterization of metric spheres as obtained in Foertsch and Schroeder [4] to a corresponding Möbius characterization of metric hemispheres.     

Random benzotrithiophene-based donor-acceptor copolymers for efficient organic photovoltaic devices

A series of benzotrithiophene-containing random terpolymers for polymer solar cells is reported. Through variations of the two other components in the terpolymers, the absorption profile and the frontier energy levels are optimized and maximum power conversion efficiencies are nearly doubled (5.14%) relative to the parent alternating copolymer.     

Synthesis of novel thieno[3,2-b]thienobis(silolothiophene) based low bandgap polymers for organic photovoltaics

Thieno[3,2-b]thienobis(silolothiophene), a new electron rich hexacyclic monomer has been synthesized and incorporated into three novel donor-acceptor low-bandgap polymers. By carefully choosing the acceptor co-monomer, the energy levels of the polymers could be modulated and high power conversion efficiencies of 5.52% were reached in OPV devices.     

Rate and Equilibrium Constants for Reactions Transferring a Dimethylcarbamoyl Group between Pyridines

We have studied 18 reactions, including four identity reactions, involving transfer of a dimethylcarbamoyl group with N-acylpyridinium bonds to pyridine and its 4-substituted derivatives in acetonitrile solutions at 298 K. The rate constants k _ij varied within the range 0.4 to 10^–6 L/mol·s; the equilibrium constants K _ij varied from 10⁷ to 10^–5. The rate and equilibrium for exchange of carbamoyl groups are described satisfactorily by the Brönsted equation. We have shown that all the reactions occur according to a forced concerted S _N2 mechanism. The structure of the transition state and its position on the reaction coordinate for identity transfer are considered using a More O'Ferrall-Jencks diagram.     

Feed Adjustment Chemistry for Hanford 101-SY and 103-SY Tank Waste: Attempts to Oxidize the Non-Pertechnetate Species

More than 50% of the technetium in Hanford 101-SY and 103-SY tank waste is not pertechnetate (TcO₄ ^–). These non-pertechnetate species (TcN) are stable, soluble, reduced complexes of technetium. In order to remediate these waste, it will be necessary to oxidize these species to TcO₄ ^–. For radioanalytical purposes, oxidation requires digestion in Ce(IV)/16M HNO₃. Many oxidants are ineffective. Sodium peroxydisulfate, sodium peroxydisulfate/silver(I), and ozone oxidize all of the technetium species to pertechnetate.     

Rate and Equilibrium of Acetyl Group Exchange between Pyridines and Pyridine N-Oxides

22 Acetyl group exchange reactions between N-acetoxypyridinium salts and 4-dimethylaminopyridine, 4-morpholinopyridine, and N-methylimidazole in acetonitrile at 298 K have been studied. The rate constants varied from 10⁵ to 10^–4 L/mol·s, and the equilibrium constants ranged from 10⁹ to 10^–9. The rates and equilibrium constants of these reactions did not comply with the Brönsted equation. The kinetics of the acetyl exchange reactions are well described by a correlation equation containing squared terms.