Why not use point charge models for the determination of bond angles?

Bond angles of several free radicals have been estimated using the point charge model together with ESR data and compared with those derived by Coulson's equation and the INDO method. The model is found to work well in predicting bond angles for most radicals just like the INDO method. Some relationships between the model and the INDO method are discussed.     

New methods and reagents in organic synthesis. 49. A highly efficient stereoselective synthesis of L-daunosamine through direct C-acylation using diphenyl phosphorazidate (DPPA)

L-Daunosamine, the carbohydrate component of a group of important anticancer anthracycline antibiotics, has been efficiently prepared from L-lactic acid in a completely stereoselective manner through direct C-acylation using diphenyl phosphorazidate (DPPA).     

Quality check of heparin injections by 1H-nuclear magnetic resonance spectroscopy

The quality of commercial heparin injections was examined by 400-MHz proton nuclear magnetic resonance (1H-NMR) spectroscopy using several measuring modes. The signals of the N-acetyl protons, as well as the sugar-ring protons, attached to the sulfamino and sulfato group-bearing carbons could be easily distinguished from other proton signals and quantified. Measuring at a high temperature (60 degrees C) enabled clear isolation of the H-5 proton signal in the sulphated iduronic acid residue (Is-5) from other proton signals including that of water. The heparin contents of various heparin injections were estimated by using this signal as an index. However, the signal intensity was not parallel with anticoagulant activity. On the other hand, the N-acetyl proton signal was highly correlated to anticoagulant activity. The present method was also useful for concurrent identification of additives in heparin injections.     

Proposed structure of the cyclic peptide dolastatin 3, a powerful cell growth inhibitor,should be revised!

The cyclic peptide proposed for the structure of the powerful cell growth inhibitory dolastatin 3, its diastereomers, and their isomers on the reverse order have been synthesized by the use of diphenyl phosphorazidate(DPPA) and diethyl phosphorocyanidate(DEPC). Their physicochemical and biological properties have shown that the proposed structure is untenable.     

Inner-valence states of N2+ and the dissociation dynamics studied by threshold photoelectron spectroscopy and configuration interaction calculation

The N2(+) states lying in the ionization region of 26-45 eV and the dissociation dynamics are investigated by high-resolution threshold photoelectron spectroscopy and threshold photoelectron-photoion coincidence spectroscopy. The threshold photoelectron spectrum exhibits several broad bands as well as sharp peaks. The band features are assigned to the N2(+) states associated with the removal of an inner-valence electron, by a comparison with a configuration interaction calculation. In contrast, most of the sharp peaks on the threshold photoelectron spectrum are allocated to ionic Rydberg states converging to N2(2+). Dissociation products formed from the inner-valence N2(+) states are determined by threshold photoelectron-photoion coincidence spectroscopy. The dissociation dynamics of the inner-valence ionic states is discussed with reference to the potential energy curves calculated.     

Synthetic Uniform Polymers and Their Use for Understanding Fundamental Problems in Polymer Chemistry

Summary: A uniform polymer is a polymer composed of molecules that are uniform with respect to molecular weight and constitution. Besides natural uniform polymers such as nucleic acids and polypeptide, synthetic uniform polymers have been obtained by a variety of approaches. In particular, a combination of living polymerization and supercritical fluid chromatography (SFC) separation is one of the promising ways for the preparation of uniform polymers. End‐functionalized uniform polymers enabled us to prepare uniform polymer architectures such as block, graft, comb, and star polymers. Their use for understanding the fundamental problems in polymer chemistry is discussed; topics include crystallization of polymers, chain conformation in solution, and association of stereoregular polymers in solution.

SFC traces of isotactic PMMA containing an authentic sample of the 45‐mer (a) and of the isolated uniform PMMA of 100‐mer (b).     

Ultimately Specific 1,4‐cis Polymerization of 1,3‐Butadiene with a Novel Gadolinium Catalyst

Novel complexes [(C₅Me₅)₂Ln][B(C₆F₅)₄] (Ln = Pr, Nd, or Gd) were prepared, which in combination with ⁱBu₃Al efficiently induce highly 1,4‐cis‐specific polymerization of butadiene. The activity of the Gd complex/ⁱBu₃Al system is high enough to exhibit good catalytic activity even at low temperature. Polymerization at −78 °C gave polybutadiene with nearly perfect 1,4‐cis microstructure (>99.9%) with sharp molecular weight distribution (M _w/M _n = 1.45) and in reasonable yield.

ORTEP drawing of 2b . Selected bond distances (Å): Pr‐F1 = 2.549(2), Pr‐F19 = 2.625(2).     

Rare earth alkyl and hydride complexes bearing silylene-linked cyclopentadienyl-phosphido ligands. Synthesis, structures, and catalysis in olefin hydrosilylation and ethylene polymerization

A series of silylene-linked cyclopentadienyl-phosphido rare earth alkyl and hydride complexes of type Me₂Si(C₅Me₄)(PR′)LnR (Ln=Y, Yb, Lu; R′=Ph, Cy, C₆H₂^tBu₃-2,4,6; R=CH₂SiMe₃, H) have been synthesized and structurally characterized, and their activity in ethylene polymerization and olefin hydrosilylation has been studied. These complexes represent the first examples of rare earth alkyl and hydride complexes bearing cyclopentadienyl-phosphido ligands, which are in sharp contrast both structurally and chemically with the analogous cyclopentadienyl-amido and metallocene complexes.