Automation of the gas analysis of14C-labelled compounds utilizing a piston-type counter tube

In this paper an automatic apparatus designed for the radioactivity measurement of¹⁴C-labelled organic compounds in the gaseous phase is described. The labelled organic compounds are combusted in a mixture of argon and oxygen. After combustion the oxygen content of the gas is eliminated by passing it through a copper packing. The water and heteroelements present are also removed and the radioactive carbon dioxide gas is swept by argon carrier gas into a piston-type counter tube. In the counter tube the piston forming a dividing wall moves forward in accordance with the rate of combustion and sweeping, and thus sucks the gases leaving the combustion tube into the effective tube volume. The anode wire is carried by a reel located in the piston and a spring device ensures its stretched state. At the end of the sweeping period methane is fed into the counter tube and the activity of the argon—methane—carbon dioxide mixture is measured in the limited proportional region. Manual and automatic operation is possible. The piston-type counter tube provides possibility for strandardization by means of extrapolation and for measurement of absolute activities.     

NMR and stereochemical studies of non aromatic heterocyclic compounds—II : 13C and 31P NMR of 2-methoxy-1,3,2-dioxaphosphorinanes

¹³C and ³¹P chemical shift data for eight 2-methoxy-1,3,2-dioxaphosphorinanes are reported. Examination of pairs of geometrical isomers, which differ only in the orientation of the OMe substituent on P^III, have shown that both the ³¹P and the ¹³C signals of C_4,6 atoms appear 3–4 ppm at higher field when the OMe is axial compared with the equatorial isomer. This observation can be associated with the 1–3 syn diaxial interaction between the phosphorus axial substituent and the axial hydrogens on C_4,6 and should thus constitute, in the future, a supplementary tool for the structural analysis of this kind of compound. Important long range δ effects were observed both on ¹³C and especially on ³¹P chemical shifts. It is suggested that the high field δ_e effects could reflect a direct stereoelectronic interaction between the P atom and the cyclic C-5 atom. This interpretation is supported by a study of the ³¹P…¹³C coupling constants and their stereochemical dependence.     

Chemiluminescent ion-molecule reactions in the system C+ + H2

The optical emission resulting from collisions between C⁺ ions and H₂ gas was measured in the energy range 2 to 20 eV_c.m.. The observed spectrum consists mainly of the CH⁺ A ¹Π → X ¹Σ⁺ band system; CH⁺ (A ^fΠ) is shown to be formed in the chemiluminescent reactio: C⁺(²P⁰) + H₂ → CH⁺(A ¹Π) + H(²S). The energy dependence of the emission cross section was measured. The occurrence of this reaction is discussed in terms of a electronic state correlation diagram for the system.     

Collision-induced rotational transitions in nali(1Π)

Collision-induced rotational transitions in the electronically excited NaLi molecule have been studied using laser excited fluorescence. Due to the greater number of allowed transitions as compared with Na₂ and Li₂, more cases were found of transitions +ΔJ and ?ΔJ having greatly different cross sections (“+/ - asymmetry”). This observation is in agreement with recent predictions on the basis of Born's approximation. All observed transitions are classified according to the symmetry of the contributing potential terms. Data are presented which indicate the necessity for refinements of the theory.     

Overtone spectroscopy of some benzaldehyde derivatives

Overtone spectrum of o, m and p-nitrobenzaldehydes and p-chlorobenzaldehyde has been studied in 2000–12000 cm⁻¹ region. Vibrational frequencies and anharmonicity constants for aryl as well as alkyl CH stretch vibrations have been determined. We have also determined the internuclear distances for the aryl CH bond in the different molecules. The small variation observed in these distances is an indication of the substitution effect. It is observed that in the case of p-disubstituted benzens, the shift in aryl CH bond is proportional to sum of the Hammet σ of the substituents. However in the case of o-disubstituted benzenes it is only 80% of the para-substituted shift.     

Carbon-13 magnetic resonance study of spiro compounds

A large series of cyclohexane and cyclopentane spiro compounds has been studied by carbon-13 NMR. Increments have been derived in terms of α, β, γ spiro substituent effects, one ring being considered as the substituent of the other. As usual α and β effects are paramagnetic and γ effects are diamagnetic. They are compared with the corresponding effects associated with the introduction of a gem dimethyl group into a cyclohexane or cyclopentane ring. The size of the two rings involved in the spirane structure has a marked influence especially on the chemical shift of the spirane carbon atom. Comparison between monospiro and dispiro derivatives gives information about the so-called 1,5 or δ effect which is paramagnetic. From an analytical point of view, carbon-13 NMR appears to be a powerful method of detecting the spirane structure, apparently including the relative size of the rings.     

L α emission from collisional excitation of H Atoms by threshold energy Ar+ ions

In a specially designed collision chamber, H atoms produced by a microwave discharge were excited into the 2p state by impact of Ar⁺ ions in a beam. A degree of dissociation up toη=94% was measured at the exit of the microwave source, although in the center of the collision cellη is smaller, with a lower limit of 33 %. The effect of vibrational excitation of H₂ by the discharge and the resulting difficulties of measuringη are discussed. The cross section forL _α emission increases linearly from the threshold, at 10.2 eV_CM, to 17.1 eV_CM. The absolute cross section at this energy is 1.5·10^?17 cm² forη=33% (with a minimum of 0.6·10^?17 cm², for the maximum possibleη). The absence of an activation barrier rules out some features shown by an earlier ab initio calculation.     

Toy model of hydrodynamic fluctuations

We study hydrodynamic fluctuations in an ideal gas. Because one is interested in thermodynamic properties of small volume elements, Einstein's theory of equilibrium fluctuations in large systems is insufficient. A toy model of correlated fluctuations in neighboring small cells leads us to the distinction of biased and unbiased momentum densities. Hydrodynamic equations that satisfy the fluctuation-dissipation theorem can then be formulated in terms of these two different momentum densities or velocities.