Symmetry allowed π4s+π2s additions silacyclopentadienes

π⁴s+π²s cycloaddition of hexaphenylsilacyclopentadiene with ethyl acrylate gives rise to a bicyclosilaheptene derivative. High resolution NMR studies have shown that the ester group in this adduct is in the endo position and that the ester methylene protons are magnetically inequivalent. Similar cycloadditions of hexaphenylsilacyclopentadiene, 1,1-dimethyl-2,3,4,5-tetraphenylsilacyclopentadiene, 1-methyl-1,2,3,4,5-pentaphenylsilacyclopentadiene, and 1-methyl-1-vinyl-2,3,4,5-tetra-phenylsilacyclopentadiene with dienophiles like acrylonitrile, maleic anhydride and dibenzoylacetylene have been carried out. The stereochemistry of these adducts has been deduced on the basis of NMR studies. Mass spectral fragmentation studies of some of the silabicycloheptenes have been carried out.     

Irreversible cathodic behavior of graphite in the presence of some mixtures of onium salts

The electrochemically induced dissolution of ferrocene in a carbon paste electrode is investigated by using chronoamperometry at constant potential. Two types of behaviour are observed, according to the initial form of ferrocene: particles or deposit. The experimental i-t curves are respectively in agreement with the theoretical curves, derived earlier, in the case of spherical particles or planar slabs of solid. The analysis of the curve shows that the process is diffusion controlled, so that the dissolution rate of ferrocene cannot be measured. The parameters calculated from the curves (thickness of the deposit, initial distance from the electrode, area) have a reasonable order of magnitude.     

Synthesis of racemic and optically active forms of lineatin,the unique tricyclic pheromone of trypodendron lineatum (olivier)

(±) - 33,7 - Trimethyl - 2,9 - dioxatricyclo[3.3.1.0^4,7]nonane 1 and (±) - 3,3,7 - trimethyl - 2,9-dioxatricyclo [4.2.1.0^4,7]nonane 2 were synthesized. The former was shown to be (±)-lineatin, an ambrosia beetle pheromone. A selective synthesis of (±)-lineatin was devised, which was modified to yield the both enantiomers of lineatin via optical resolution of an intermediate.     

Concerted cycloaddition of chlorosulfonyl isocyanate to α-pinene stepwise rearrangement of the β-lactam cycloadduct to a γ-lactam

Chlorosulfonyl isocyanate adds to α-pinene in concerted fashion to give the unrearranged N-chlorosulfonyl-β-lactam 2 (75%). Thermolysis of cycloadduct 2 affords the rearranged N-chlorosulfonyl-γ-lactam 6 (60%) via a sequence of transient carbonium ions (45). Reductive hydrolysis of 2 and 6 gave, respectively, the NH-β-lactam 3 (70%) and the NH-γ-lactam 7 (70%). Proof of structure of the rearranged γ-lactams 6 and 7 are provided, respectively, by X-ray crystallographic analysis and the application of the Eu(dpm)₃ NMR shift reagent.     

He I (584 Å) photoelectron spectra and photoionization cross sections of atomic chlorine and bromine

Well-resolved He I photoelectron spectra of atomic chlorine and bromine have been obtained without serious background electrons, giving rise to relative photoelectron intensities associated with differential photoionization cross sections at an angle of 90° with respect to the incident 584 Å radiation.     

Structural refinements of praseodymium and neodymium orthophosphate

The crystal structures of PrPO₄ and NdPO₄ have been determined by single crystal X-ray diffraction techniques. The structures are isostructural with CePO₄ and LaPO₄, and are monoclinic in space group $\text{P2}{}_1\text{n}$. The cell constants are a = 6.741(3), b = 6.961(4), c = 6.416(3) Å, and β = 103.63(3)° for PrPO₄ and a = 6.722(1), b = 6.933(1), c = 6.390(2) Å, and β = 103.72(2)° for NdPO₄. The least-squares structural refinements of PrPO₄ and NdPO₄ yielded R values of 0.034 and 0.038 based on 810 and 947 unique reflections, respectively. The lanthanide metal atoms are coordinated with nine oxygens and are linked together by very slightly distorted tetrahedral phosphate groups. The nine oxygen atoms ligating the lanthanide atoms form a polyhedron that is best described as a pentagonal interpenetrating tetrahedron.     

Electrochemical oxidation of 9-methylxanthine

The electrochemical oxidation of 9-methylxanthine proceeds via four voltammetric oxidation peaks at the pyrolytic graphite electrode. The first voltammetric oxidation peak (peak I_a) is a 1e reaction giving a radical which dimerizes to 8,8′-bi-9-methyl-9H-purine-2,6-(1H, 3H)-dione. Peak II_a is a further 2e electrooxidation of the peak I_a dimer to another yellow dimer 8,8′-bi-9-methyl-9H-purine-2,6-(1H)-dione-3,5-(3H)-diiminylidene. This dimer is not very stable and it hydrolyzes to 1-methyl allantoin. Peak III_a is an adsorption pre-peak to peak IV_a which corresponds, overall, to a direct 4e?4H⁺ electrooxidation of 9-methylxanthine to an unstable diimine of 9-methyluric acid. Hydrolysis of this diimine leads to a variety of ultimate products.     

Low temperature spectroscopic observation of oxygen-protonated troponeiron tricarbonyl complexes

Troponeiron tricarbonyl and 7-methyltroponeiron tricarbonyl undergo kinetically controlled oxygen protonation at low temperatures to give the corresponding hydroxytropyliumiron tricarbonyl cations, observable by ¹C and ¹H NMR spectroscopy. At higher temperatures, the oxygen-protonated species isomerize to yield the thermodynamically more stable carbon-protonated pentadienyliron tricarbonyl cations.     

Spectrophotometric determination of phosphate by extraction of reduced molybdoantimonylphosphoric acid with acetophenone-chloroform

A 90% ($\text{v}\text{v}$) mixture of acetophenone-chloroform is an effective extractant for reduced molybdoantimonylphosphoric acid. The extraction is quantitative over the acidity range of 0.04 to 4.8 N sulfuric acid. The mixed solvent extractant is virtually immiscible with water and can be used at aqueous/organic volume ratios from 1:1 to 40:1 with no loss of solvent or decrease in % extraction. Phosphate is easily determined from 5 to 1000 ppb. No interference from silicate was experienced.     

A high pressure thermobalance

A high pressure thermobalance was assembled by placing a DuPont Model 950 balance into a stainless steel enclosure. The thermobalance is capable of operation to a maximum pressure (of N₂) to 500 atm and to a maximum temperature of 500°C. Operation of the instrument is illustrated by the thermogravimetric curves of BaBr₂·2H₂O, CuSO₄·5H₂0 and NaHCO₃ at various pres