Regioselective carbon-carbon bond formation at C2 of 1,3-thiazole by reaction of n-ethoxycarbonylthiazolium chloride with C-nucleophiles

N-Ethoxycarbonylthiazolium chloride generated $\text{in situ}$ from 1,3-thiazole and ethyl chloroformate, treated with lithium carbanions of esters, Grignard reagents, silyl enol ethers and esters, undergo nucleophilic addition at C₂ affording the corresponding 2-substituted N-ethoxycarbonylthiazolines.     

Spectroscopic properties of Tm3+ in fluorophosphate glasses

The optical properties of Tm³⁺ in a fluorophosphate glass are reported. Oscillator strengths and Ω_λ parameters for Tm³⁺ were calculated. Energy transfer between Ce³⁺ → Tm³⁺, Tm³⁺ → Eu³⁺ and Tm³⁺ → Tb³⁺ were measured at room temperature and interpreted using the Yokota and Tanimoto scheme. Fluorescence decay results seem to support the hypothesis of a diffusion-limited relaxation. The effects of Tb³⁺ and especially Ce³⁺ on the fluorescence of Tm³⁺ ion point out the interest of these dopants for obtaining a better emission of Tm³⁺ at 450 nm.     

Ground-state properties of the antiferromagnetic potts model in an external field

The ground-state properties of the antiferromagnetic q-state Potts model in an external field are studied. At the upper critical field this model may be mapped onto a hard-core lattice gas with activity z = q ?1. This allows us to get some exact results for the triangular lattice on which the corresponding hard hexagon problem has been recently solved by Baxter.     

A note on reflexivity in Banach spaces

For any normed spaceX, the unit ball ofX is weak *-dense in the unit ball ofX ^**. This says that for any ε>0, for anyF in the unit ball ofX ^**, and for anyf ₁,…,f _n inX ^*, the system of inequalities |f _i(x)?F(f _i)|≤ε can be solved for somex in the unit ball ofX. The author shows that the requirement that ε be strictly positive can be dropped only ifX is reflexive.     

Synthesis and Mesomorphic Properties of 2,6-Disubstituted Tetralins

Synthesis and mesomorphic behavior of nine members of each of the two classes of 6-phenyl- and 2-phenyltetralins and five members of the 2-trans-cyclohexyltetralins are reported. The synthesis of one member of each class is described in detail. Besides the target compounds, more than twenty intermediates showed liquid crystalline properties; their transition temperatures are recorded (see Tables 1-6).     

Reactivity of β-aluminas with water

The reactivity with air moisture of finely divided crystals of Na β and Li⁺-containing β-aluminas is analyzed with thermogravimetric and X-ray techniques. For Na β-alumina two distinct water intake processes are evident: 1) a fast one, controlled by the elastic interactions among water molecules near the crystal boundaries; 2) a slow one, driven by water diffusion away from the boundaries. For finely divided crystals of Li β-alumina the two processes cannot be distinguished but the slow one is observable in crystals of macroscopic dimensions. The water intake is generally accompanied by an expansion of the c-axis. However, the relationship between water content and c-parameter is highly non-linear and the c-axis length at room temperature depends upon the thermal history of the sample. Our results confirm previous reports suggesting that β-aluminas absorb about one water molecule per cation of the conducting plane.     

Sulle « catene » di numeri primi consecutivi a differenza limitata

Sunto Si considerano certi aggregati di numeri primi consecutivi, le cui differenze soddisfano a particolari disuguaglianze; aggregati a cui si attribuisce il nome di ? catene ?. Fra i vari tipi di catene (caratterizzate dalle disuguaglianze a cui soddisfano i numeri primi in esse contenuti) se ne studiano in particolare alcuni per i quali si giunge a fissare qualche limitazione relativa all'ampiezza massima della catena, oppure al numero delle catene presenti in un certo intervallo.