Methylmethacrylate complexes of sterically hindered aluminum aryloxides: activation of methacrylic esters

The interaction of AlR₂(BHT)(OEt₂) and AlMe(BHT)₂ with methylmethacrylate (MMA) leads to the formation of the Lewis acid-base complexes AlR₂(BHT)(MMA) [R = Me (1), Et (2)] and AlMe-(BHT)₂(MMA) (3), respectively. The molecular structure of 1 has been determined by X-ray crystallography. The decrease in the C=O and C=C stretching frequencies in the IR spectrum, and downfield shift in the ¹³C NMR spectrum of the - and γ-carbons of the MMA, when compared to free MMA, is presented with respect to the activator ability of sterically crowded aryloxide compounds of aluminum to aluminum-porphyrin catalyzed (Inoue) polymerization of MMA.     

ESR study of free radicals in some new hydrazones of terpenoids class

The effect of gamma-irradiation on some new hydrazones of terpenoids using electron spin resonance (ESR) is reported. Gamma-irradiation of three derivates of hydrazone and of compounds resulting from the condensation of these derivates with terpenoids produces stable free radicals at room temperature. The analysis of the ESR parameters (g-factors and hyperfine coupling) and the simulation performed lead us to conclude that free radicals are of form R–N–NH₂ (arising from hydrazine derivates) and R–N–N=R (arising from condensation compounds). The thermal stability of formed radicals is discussed and the activation energy involved in the process of recombination of free radicals is calculated.     

Second Dissociation Constants of 4-[N-morpholino]butanesulfonic Acid and N-[2-hydroxyethyl]piperazine-N′-4-butanesulfonic Acid from 5 to 55°C

The values of the second dissociation constant, pK ₂, for the dissociation of the NH⁺ charge center of the zwitterionic buffer compounds 4-(N-morpholino)butanesulfonic acid (MOBS), and N-(2-hydroxyethyl)piperazine-N-4-butanesulfonic acid (HEPBS) have been determined from 5 to 55°C, including, 37°C at intervals of 5°C. The electromotive-force (emf) measurements have been made utilizing hydrogen electrodes and silver–silver chloride electrodes. The value of pK ₂ for MOBS was found to be 7.702 ± 0.0005, and 8.284 ± 0.0004 for HEPBS, at 25°C, respectively. The related thermodynamic quantities, G ^o, H ^o, S ^o, and C _p ^o for the dissociation processes of MOBS and HEPBS have been derived from the temperature coefficients of pK ₂. Both the MOBS and HEPBS buffer materials are useful as primary pH standards for the control of pH 7.3 to 8.6 in the region close to that of physiological fluids.     

Crystal and molecular structure ofS-methyl(pentafluorosulfanyl)thiocarbamate

The X-ray structure of S-methyl(pentafluorosulfanyl)thiocarbamate, SF₅NHC(O)SCH₃, has been determined from three-dimensional diffractometer data and refined by full-matrix least-squares techniques. The crystals are monoclinic:P2₁/m,a=5.008 (5),b=7.811 (2),c=9.348 (4) Å, =99.08 (7)°, andZ=2; finalR=0.046 for 517 observed reflections. The structure comprises hydrogen-bonded (NHO) chains with the component monomers in thecis, cis-conformation, i.e., the arrangement of the nonhydrogen and nonfluorine atoms is nearly planar, the SF₅ group and the O are in acis position with respect to the C-NH bond, and the O and the CH₃ group are in acis position with respect to the C(O)-S bond. Theoretical methods including MNDO and molecular modeling were used to study the relative stabilities of the four possible conformations of SF₅NHC(O)SCH₃.     

Lifshitz tails for periodic plus random potentials

We prove that the integrated density of states () for a potentialW =V _per +V has Lifshitz tails where V_per is a periodic potential with reflection symmetry andV is a random potential, e.g., of the formV =q _i ()f(x–i).research partially supported by DFG.research partially supported by USNSF under grant No. MCS-81-20833.