Delocalization resonance energy of the allylic radical from the geometrical isomerization of hexa-1,3,5-trienes

Thermal cis, trans geometrical isomerization theoretically involves a 90° twisted, singlet diradical-like transition state which may serve as a base for the examination of structural perturbations. Although thermal rearrangement of hexa-1, trans-3,5-triene (and all-trans octa-2,4,6-triene) to the cis isomer cannot be followed directly owing to subsequent cyclization and 1,5 hydrogen shifts, activation parameters for disappearance have been determined. Experimental complications and mechanistic uncertainties which make interpretation difficult are removed in the bicyclic hexatriene, cyclopentenylidenecyclopentene. These geometrical isomers undergo uncomplicated thermal cis, trans isomerization in vessels of lead-potash glass: log k₁ = 12·03±0·32?41·7±0·8/(0·004575T_abs). Extraction of a value for allylic delocalization energy from the behavior of hexa-1, trans-3,5-triene [log k₁ = 12·91 ± 0·47?44·3±1·2/(0·004575 T_abs)] requires corrections of the Dewar-Schmeising type for changes in hybridization of the σ bonds. Depending on whether ethylene or trans-butene is taken as standard, values of 12·2 and 13·1 kcal/mol are obtained (estimated uncertainty ± 2 kcal/mol).     

A mechanistic explanation for the SO2 oxidation rate data of a Cs/V catalyst at high pressures and conversions

A preliminary attempt to modify a molybdena-silica for ethylene homologation was performed by adding copper. Ethylene homologation (3C₂H₄2C₃H₆) was enhanced 2.5 times on copper doped catalyst. Contrary to this, ethylene metathesis (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) was suppressed in the presence of copper. The selectivity of the homologation to metathesis was increased 7.5 times.

---

- , (3C₂H₄2C₃H₆), . 2,5 , (C₂H₄–¹²C₂+C₂H₄–¹³C₂2C₂H₄–¹³C₁) . 7,5 .

     

Direktthermometrische bestimmung von thorium und lanthan in gläsern

A rapid method is described for the determination of thorium and lanthanum in non-silicate glasses. It is suitable for routine use in a works laboratory. The samples are dissolved in nitric acid. The thorium content is calculated from the measured heat of precipitation of thorium iodate, and the lanthanum content by difference from the heat of precipitation of both thorium and lanthanum oxalates together. The apparatus is calibrated by using standard solutions of the two metal ions. The standard deviations for the middle of the range (around 250 mg of the oxides) were 3·1 mg for ThO₂ and 1·7 mg for La₂O₃. An analysis takes about 1·5 hr.