Crystal and Molecular Structure of (±)-8,8-Dimethyl-6,7-diazabicyclo[3.3.0]octa-1,6-diene 7-oxide

The exclusive product of thermal rearrangement of (±)-7-isopropylidene-2,3-diazabicyclo[2.2.1]hept-2-ene N-oxide (2) has been identified as the title compound (1). The compound crystallizes in the orthorhombic space group Pbca (No. 61), with a= 8.953 (2), b= 12.740 (2), c=14.446 (3) Å; Z= 8; p_x=1.227 g cm^?3. The details of the molecular structure are not unusual, except for a long C–N distance (C(8)–N(7), 1.560 (4) Å). No significant short intermolecular contacts are observed in the crystal.     

Photometric investigation of precipitation titrations

Photometric investigation of precipitation reactions, by automatically recording the changes in absorbance of a stirred suspension with titrant added, showed that end-points and reacting mole ratios are quickly and easily evaluated. Quantitative analysis in the concentration range 10^-2 to 10^-4M is possible with an error of about 1%. The use of breaks in titration curves to formulate intermediate reaction products is doubtful. A rapid change in the physical form of the precipitate is a limitation of the method.     

Stochastic-network Reduction and Sensitivity Techniques in a Cost Effectiveness Study of a Military Communications System

This paper describes some aspects of cost effectiveness methodology and operational research as they have been applied in a system design study for a military communications system. There are two main areas of interest from an operational research point of view:(a) The attempt to use cost effectiveness analysis as an integral part of system design.(b) The development and application of new techniques (notably in stochastic network analysis and simulation) which are potentially of much wider application.There are several ways of attacking the problem of multiple objectives encountered in a cost effectiveness analysis. These are briefly described and the preferred method of a single measure of effectiveness is discussed in detail. The measure used in the communications system design study is presented and the method of evaluating it by simulation is described. The next step after evaluation of the effectiveness is optimization and here the use of the Lagrange multipliers is introduced. This method requires iteration on the values of performance parameters and their costs and this becomes very time-consuming if a simulation must be performed each time. It is here that the novel methods of analysing networks are developed. The main use of these methods of analysis, or reduction rules, has been in reducing the size and complexity of the simulations. The technique which has contributed most to the reduction in the number of simulations required to arrive at an optimum disposition of resources is a method of carrying out a sensitivity analysis based on data collected during a single simulation run. This hybrid analytical-cum-simulation technique is discussed in detail with reference to a communications system, and its application to a wider range of problems, such as probabilistic PERT, indicated.     

Noise-induced threshold shift and cochlear pathology in the Mongolian gerbil

Groups of six mongolian gerbils were exposed to two-octave (1414-5656 Hz) band noise for 1 h at 100, 110, and 120 dB SPL. Threshold shift at several frequencies was measured 0.5, 3, 6, and 12 h, and 1-28 days after exposure. Final thresholds were determined at least two months postexposure. Extensive threshold shift was observed in all groups 0.5 h after exposure (TS0.5h). Where threshold shift increased in the initial hours after exposure, such increases were correlated with eventual permanent threshold shift (PTS). Recovery of thresholds from 1-28 days after exposure was approximately exponential, and slowest at the edges of the exposure band. PTS was seen in the 110 and 120 dB SPL groups. With TS0.5h of 50 dB or less, no PTS resulted. With TS0.5h above 50-60 dB, eventual PTS increased linearly with a slope of about 1.25 PTS/TS0.5h. Cochlear damage was evaluated by light microscopy. The relationship between hair cell loss and PTS was consistent with an inner hair cell threshold about 40 dB higher than that of outer hair cells. It is suggested that recovery from noise-induced threshold shift may involve different mechanisms in the two types of hair cells.     

Time-dependence of the electron-impact-induced unimolecular decay process C3H8+ → C3H7+ + H

A time-of-flight mass spectrometer has been modified to study directly the time dependence of metastable decay processes by introducing a variable time delay between the ionization and extraction pulses and by providing a set of retarding plates and grids in the flight tube to select a single parent ion species for study and to resolve the peak into parent ion, daughter ion and daughter neutral components. The experimentally determined time dependence of the unimolecular decay process C₃H₈⁺ → C₃H₇⁺ + H is compared with previously published predictions of the quasiequilibrium theory of mass spectra.     

Higher order speciation effects on plutonium L(3) X-ray absorption near edge spectra

Pu L(3) X-ray near edge absorption spectra for Pu(0-VII) are reported for more than 60 chalcogenides, chlorides, hydrates, hydroxides, nitrates, carbonates, oxy-hydroxides, and other compounds both as solids and in solution, and substituted in zirconolite, perovskite, and borosilicate glass. This large database extends the known correlations between the energy and shape of these spectra from the usual association of the XANES with valence and site symmetry to higher order chemical effects. Because of the large number of compounds of these different types, a number of novel and unexpected behaviors are observed, such as effects resulting from the medium and disorder that can be as large as those from valence.     

Synthesis of stereoisomeric medium-ring alpha,alpha'-dihydroxy cycloalkanones

The stereochemical course of the epoxidation of the silyl enol ethers of 2-tert-butyldimethylsilyloxycycloheptanone and -cyclooctanone has been investigated and shown to proceed exclusively anti to the existing alpha-substituent. 2-(Benzyloxy)cyclooctanone behaves similarly, and the presence of a transannular double bond does not alter the outcome. Alpha-ketol rearrangements are seen to operate during ensuing fluoride ion-induced removal of the silyl protecting groups in select examples. The preferred means for generating the cis isomers of the alpha,alpha'-dihydroxy cycloalkanones involves methylenation of the monoprotected trans-dihydroxy ketones with the Nysted reagent, followed by oxidation and subsequent reduction with sodium borohydride. Ozonolysis and fluoride ion-induced desilylation complete the route.     

Tuning selectivity in macrotricyclic carbohydrate receptors; CH-->N mutations in aromatic spacers

Dipicolinoyl spacer groups are used to control the conformational and H-bonding properties of tricyclic carbohydrate receptors 3 and 4. Binding selectivities are changed in relation to all-isophthaloyl system 1b.