Cooperative and competitive effects of substituents at C1 and C4 on the barriers to ring inversion of 5,5-difluorobicyclo[2.1.0]pentanes

To identify the reasons for the very low barrier that has been measured for ring inversion of 1,4,5,5-tetrafluorobicyclo[2.1.0]pentane (deltaG(double dagger) = 6.8 +/- 0.2 kcal/mol), CASSCF and CASPT2 calculations have been performed on ring inversion in this and other bicyclo[2.1.0]pentanes. The results of the calculations show that a cooperative interaction between the geminal fluorines at C2 and the fluorines at C1 and C3 in the singlet cyclopentane-1,3-diyl transition structure (TS) contributes 3.7 kcal/mol to lowering the barrier to ring inversion in the tetrafluoro compound. In contrast, a competitive substituent effect in the TS for ring inversion of 1,4-dicyano-5,5-difluorobicyclo[2.1.0]pentane is predicted to raise the barrier height by 6.1 kcal/mol. The origin of these cooperative and competitive substituent effects is discussed.     

Study of alpha-crustacyanin utilizing halogenated canthaxanthins

[structure: see text] The preparations and spectroscopic characteristics of five all-trans halogenated canthaxanthins are described in this letter. The air/light-sensitive halogenated canthaxanthins were used to study alpha-crustacyanin, a blue astaxanthin-protein complex, which is isolated from the carapace of the lobster. Steric and electronegative effects of the halogen substituents on the noncovalent interaction between astaxanthin and the protein in alpha-crustacyanin were observed.     

Electron spin resonance on GdxMo6Se8 (x = 1.0 and 1.2)

Electron spin resonance of Gd³⁺ in Gd_xMo₆Se₈ (x = 1.0 and 1.2) has been measured in X-band and in K-band between 1.4 and 290 K. The results indicate that the conduction electron - Gd³⁺ spin exchange coupling constant is positive and equal to +0.011 eV, in agreement with previous determinations based on superconductivity and static magnetic susceptibility measurements.     

Orthogonal Polynomials and Second-order Differential Equations

We show that a sequence of polynomials can be eigenfunctionsof a second-order differential operator only under severe restrictions.     

Direct observation of long range ferromagnetic order in the reentrant superconductor HoMo6S8

The neutron scattering technique has been used to investigate the magnetic properties of the ternary Chevrel-phase superconductor HoMo₆S₈. Magnetic critical scattering is observed in the superconducting phase, with the magnetic correlation range increasing with decreasing temperature. At the transition in which the normal state is reentered, the system is found to develop long range ferromagnetic order, with a saturated magnetic moment at low temperatures of 9.06 ± .3 μ_B and the spin direction along the unique [111] trigonal axis.     

Phase transition in the superconducting state in Gd-rich pseudoternary compounds (La1-xGdx)1.0Mo6Se8

A pronounced lambda-type specific heat anomaly in the superconducting state is reported for Gd-rich pseudoternary compounds (La_1-xGd_x)_1.0Mo₆Se₈. The anomaly is very similar to that previously reported for the compound Gd_1.2Mo₆Se₈. Both the temperature of the lambda anomaly (≈ 3.5 K) and the Curie-Weiss temperature were found to be nearly independent of x. In addition, evidence for the occurence of magnetic ordering at 0.8 K in Gd_1.2Mo₆Se₈ is presented. These observations support our earlier conjecture that the lambda anomaly at 3.5 K does not arise from magnetic ordering of the Gd³⁺ ions. The anomaly appears instead to be due to a different type of phase transition which is associated with the presence of the localized 4f electrons of the Gd³⁺ ions, but the exact nature of the transition remains to be established.     

Levels in Gd158 from the (d,p) reaction

The nuclear spectroscopy of Gd¹⁵⁸ has been investigated by deuteron stripping with magnetic analysis of the resulting protons. Over fifty levels have been observed. Comparison is made of observed and theoretical relative cross sections. Two new rotational bands have been observed; one band based on the 2+ two-quasiparticle state [521 +] – [521?] at 2333.6 keV and a second band based on the 1 + two-quasiparticle state [521 +] – [521?] at 2494 keV. The ground state (d,p)Q-value was found to beQ _o=5706± 5 keV.     

Reentrant superconductivity in the orthorhombic system (Tm1−xLux)RuB2

The boundaries between the paramagnetic, superconducting and magnetically ordered phases in the orthorhombic pseudoternary system (Tm_1?xLu_x)RuB₂ have been established by means of ac magnetic susceptibility measurements down to 1.2 K. Reentrant superconductivity occurs between x = 0.52 and x ? 0.68. The absence of coexistence between superconductivity and long range magnetic order in this region suggests a ferromagnetic-like nature of the magnetic state. The initial linear depression of superconducting transition temperature (T_c) gives a coupling constant value N(E_F)$\text{J}$² between conduction electrons and magnetic Tm³⁺ moments of 6.7 × 10^?4 eV-atom-states/ spin direction.     

Fourier transform infrared studies of inhibited autoxidation in cis-1,4-polybutadiene

The inhibited autoxidation of cis-1,4-polybutadiene (BR) was examined by Fourier transform infrared spectroscopy (FTIR) in the presence of three chain-breaking antioxidants: 2,6-di-tert-butyl-4-methylphenol (CA-1); 4,4′-methylene-bis-(2,6-di-tert-butylphenol) (CA-2) and N-phenyl-2-naphthylamine (CA-3). Weak interaction is detected between the phenolic OH and arylamine NH groups and the rubber unsaturation. These antioxidants terminate two or more kinetic chains per molecule and their mechanisms are described.