Heliuim-3 mass spectrometry for low-level tritium analysis of environmental samples

Helium-3 (³He) mass spectrometry for the analysis of low-level tritium (³H) concentrations (0.5 to 5 Bq·l^–1) in environmental sample matrices was compared with conventional low-level -decay counting methods. The mass-spectrometry method compared favorably, equalling or surpassing conventional decay-counting methods with respect to most criteria. Additional research and method refinements may make³He mass spectrometry the method of choice for routine, low-level to very-low-level (L<0.5 Bq·l^–1)³H measurements in a wide variety of environmental samples in the future.     

The nature of the product from the reaction of tetracyanoethylene with iron pentacarbonyl

The reaction of tetracyanoethylene with iron pentacarbonyl in mesitylene at 90° gave an insoluble product, Fe₂C₁₆H₁₂N₈O₇. The Mössbauer and IR spectra, the magnetic susceptibilities over the temperature range 95–298 K, and the thermal decomposition temperatures in a nitrogen atmosphere were measured. The solid is best described as an iron (III) ketoamine polymer with hydroxo bridges between iron atoms.     

Reactions of (Z)-3-aryl-3-chloropropenals with nucleophiles: stereoselective formation of (E)-vinylogous esters, (E)-vinylogous amides, and vinamidinium salts

The highly stereoselective conversions of (Z)-3-aryl-3-chloropropenals to (E)-3-alkoxy-3-arylpropenals, to (E)-3-aryl-3-morphorlinopropenals, and to vinamidinium salts are reported. The stereochemical assignments were based on 2D-NMR experiments.     

Development and application of computerized battery-powered field programmable data acquisition systems

A computer-based, battery powdered, data acquisition system is described, which forms part of a field-based chemical system for use with sensors generating a voltage. The equipment has been developed using complementary metal oxide semiconductor (CMOS) “low power” integrated circuit technology and is based on a multiplexed bus. One 2k-byte erasable programmable read only memory (EPROM) controls the data acquisition process. Another 2k-byte EPROM contains the monitor program, while a 2k-byte random access memory stores the data before and after manipulation. A microprocessor unit provides all the control signals used by the instrument and data are collected on a real-time basis. The electronics are housed in a self-contained box to which the sensors and an independent keyboard can be connected. The instrument can be linked with as many as eight sensors. With the use of battery-operated CMOS technology, the measurement noise level is low and analytical techniques can be used to determine low concentrations of variables in the field. The viability of the instrument has been demonstrated by obtaining extensive data on the measurement of temperature and pH. Field-based potentiometric titrations, ion-selective electrode applications and studies on battery life are also reported.     

High resolution glass capillary columns for the gas chromatographic analysis of alditol acetates of neutral and amino sugars

The development of improved high resolulation glass capillary columns for separating the alditol acetates of neutral and amino sugars is described. Different capillary column treatments were evaluated for their activity toward amino sugar derivatives and for their effect on the efficiency of the completed column. The simple two-step procedure of leaching with aqueous hydrochloric acid and dynamic coating with SP-2330 was found to produce efficient and inert columns.     

An esr study of the photoreaction of nitroalkanes with tetraphenylbiphosphine and tetraethylpyrophosphite

Some paramagnetic species formed in the photoreactions of nitroalkanes with P-compounds have been characterized by ESR. The observed radicals are mostly nitroxides whose structures are consistent with the trapping of P-centred radicals by intermediate nitroso compounds.     

1,2-Eliminations from (CH3)2NH+CH2CH3 and (CH3)2NH 2+ : Guided dissociations

1,2-Eliminations are a varied and extensive set of dissociations of ions in the gas phase. To understand better such dissociations, elimination of CH₂=CH₂ and CH₃CH₃ from (CH₃)₂NH⁺CH₂CH₃ (1) and of CH₄ from (CH₃)₂NH₂⁺ are characterized by quantum chemical calculations. Stretching of the CN bond to ethyl is followed by shift of an H from methyl to the bridging position in ethyl and then to N to reach (CH₃)₂NH₂⁺ + CH₂=CH₂ from 1. CH₃CH₃ elimination by H-transfer to C₂H₅⁺ to form CH₃NH⁺=CH₂ + CH₃CH₃ also takes place. (CH₃)₂NH₂⁺ eliminates methane by CN bond extension followed by β-H-transfer to give CH₂=NH⁺ + CH₄. Low-energy reactions resembling complex-mediated 1,2-eliminations occur and constitute a hitherto largely unrecognized type of reaction. As in many complex-mediated reactions, these reactions transfer H between incipient fragments. They are distinguished from complex-mediated processes by the fragments not being able to rotate freely relative to each other near the transition state for reaction, as they do in complexes. Most 1,2-eliminations are ion-neutral complex-mediated, occur by the just described lower energy reactions, have 1,1-like transition states, or utilize highly asynchronous 1,2 transition states. All of these avoid synchronized 1,2-transition states that would violate conservation of orbital symmetry.