Ring inversion in fluoro-cyclohexanes

Rates of ring inversion in some isomeric octa- and deca-fluorocyclohexanes and in perfluorocyclohexane have been determined by dynamic ¹⁹FNMR spectroscopy and compared with data for other compounds. ΔG²_cb varies over the range 39–49 kJ mol^-1. Surprisingly the barriers in the diastereomeric octafluorocyclohexanes lie at opposite ends of the range. It seems that 1,3-diaxal interactions are less important than supposed hitherto; other factors which may affect the barriers are discussed.     

Gold nanorods surface modified with poly(acrylic acid) as a template for the synthesis of metallic nanoparticles

Poly(acrylic acid) (PAA) surface-modified gold nanorods, contained in deionized ultra filtered (DIUF) water, served as templates for the formation of gold (Au), palladium (Pd), and platinum (Pt) nanoparticles upon reduction with NaBH₄. This provided nanoparticles with respective diameters of 7.0 ± 0.7, 4.1 ± 0.4, and 5.1 ± 0.5 nm. Varying amounts of Pt metal salt were used in EG, which acts as both a solvent and a reducing agent, ranging from 0.1, 0.2, and 1.0 mg/mL, to provide control over nanoparticle diameters of 2.0 ± 0.5 nm, to 4.0 ± 0.5 nm, and 6.2 ± 1.9 nm, respectively. Nanoparticle diameter was also controlled in DIUF water by varying the amount of Pt metal salt from 0.1, 0.2, and 1.0 mg/mL, producing Pt particle diameters, respectively, increasing from 2.7 ± 0.3 nm to 4.1 ± 0.5 nm, and 6.0 ± 0.6 nm.     

Physico-chemical characterization of a cellulosic fraction from sugar beet pulp

The residue of sugar beet pulp from which pectin and alkaline soluble polysaccharides have been removed by microwave assisted extraction or conventional heat was treated with sodium monochloroacetate under alkaline pH to convert the residual cellulose present to carboxy methyl cellulose (CMC). Weight average molar masses ranged from about 96 to 220 × 10³ Daltons, weight average intrinsic viscosity from 1.9 to 4.1 dL/g and degree of substitution from 1.38 to 0.59. HPSEC with online molar mass detectors and Atomic Force Microscopy revealed that CMC was comprised of aggregated linear moieties in contact with spherical bodies. The linear portion was a mixture of rods and segmented rods. Some of the rods had long branches.     

New high-energy luminescence bands from Co2+ in ZnSe

Three sharp absorption features in the energy range 2.36–2.55 eV have been detected in the transmission spectrum of Co-diffused ZnSe, and a number of luminescence transitions originating from the lowest of these states at 2.361 eV have been observed. Photoluminescence excitation spectra prove that these are high energy excited states of the Co²⁺_Zn impurity, a conclusion confirmed by comparison of measured and predicted luminescence energies. This represents the first identification of luminescence branching from a higher excited state of a transition metal ion in any semiconductor. The sharp, weakly phonon-coupled transitions involve either intra-impurity excitation or transitions from the impurity to localised states split off from a minimum in the conduction band. The implications of these observations for the mechanism of host-impurity energy transfer and for the nature of the excited state wavefunctions are discussed.     

p-Anisyl group: A versatile protecting group for primary alcohols

A primary alcohol can be protected as a highly stable p-anisyl ether, which undergoes mild oxidative deprotection by ceric ammonium nitrate.     

A study of the reaction pp → π− π+ at 10 GeV/c

The reaction $\text{p}\text{p}\text{→ π}{}^{\mathrm{?}}\text{π}{}^{\mathrm{+}}$ has been studied at 10.1 GeV/c in the ?t interval from 0.15 to 1.5 (GeV/c)². A line-reversal comparison with backward elastic scattering π⁺p → pπ⁺ shows good agreement for ?t > 0.3 (GeV/c)².     

The action of elemental fluorine on polyfluoro-olefins and -aromatic compounds. Part II The fluorination of decafluorocylohexene and octafluorocyclohexa-1,4- and -1,3-diene

The title compounds have been fluorinated with elemental fluorine of low oxygen content to give products derived from fluorine addition, accompanied by dimerisation and oligomerisation of radical intermediates in the case of the dienes. The 1,4-diene is relatively unreactive towards fluorine and polymerisation did not occur. Acid fluorides, of the type formed using fluorine produced without precautions to minimise oxygen-containing species, were not produced in these reactions.