Thermal tritium atom

Apart from isotope effects, the reactions of the thermal tritium atoms are, of course, identical with those of thermal hydrogen or deuterium atoms. The most important two thermal reactions are abstraction, to form HT, and addition to double bonds, the latter leading to labeled saturated and unsaturated compounds. 

An equally useful technique, and the one most commonly used, is to add a scavenger, such as iodine, bromine or oxygen. If the concentrations of these are kept sufficiently low, they will not interfere with hot reactions but they will scavenge thermal tritium atoms and the thermal addition products of olefins. They will also suppress the concentration of radicals produced by the over-all radiation to the system during isotope production. Examples of scavenger action are given in Table 4. 

The second reactant to consider is the tritium atom after its energy has been degraded to the point where its reactions become indistinguishable from those of a thermal tritium atom. 

Results with inert moderators also support the view that some of the abstraction and all of the substitution reactions are hot . Helium is an effective non-reactive moderator for tritium since its mass is close to that of tritium (cf. Section II, E). As the concentration of helium in an organic system being subjected to tritium recoils is increased, the probability of a reactive encounter between a hot tritium atom and the substrate is decreased. Product distributions should shift in the direction of what might be expected from thermal tritium atoms. In the presence of helium the yield of HT (Eq. (8)) goes up and the yield of RT (eqs. (9) and (13)) goes down (cf. Estrup and Wolfgang, 1960b) in accordance with what one would predict. 

This reaction was studied thermally and found to have relatively low activation energy. In the case of thermal deuterium atoms, they did not show any exchange of D for H in the cyclopropane molecules ", indicating that reaction 51 has high activation energy. The kinetic energy of the hot tritium atom was found to overcome this activation energy, as 16 % of the hot tritium produced in the presence of c-CaH is incorporated in T-cyclopropane (equation 56) ... 

The recoil chemistry of tritium is perhaps one of the best understood in terms of a clear idea of the product spectrum under various conditions. Realistic models have been tested and correlations with theoretical approaches have been made. Thermal-neutron absorption reactions of lithium-6 and helium-3 have been used to produce hot tritium atoms. Some physical parameters are listed in Table 2. 

E. Dovble-Bond Addition Reactions Reactions of recoil tritium atoms in alkenes have been studied and have brought to light an additional reaction type. The energetic tritium atom can add to the double bond. Urch and Wolfgang (1959) have substantiated this hot addition by studying scavenger and moderator effects in alkenes. Decomposition of the hot radical once formed follows a pattern similar to that of the decomposition of thermally excited free radicals, namely... 

A convenient way of thinking about the physical aspects of the probability of these hot reactions is stated by Rowland et al. (1961). A simple plot of reaction probability versus kinetic energy of the tritium atom is given in Fig. 3. The shape of the curve is unknown, as are the exact values of the energies where the probabilities are essentially zero. The action of the moderator in decreasing the number of collisions necessary to thermalize the atom and thereby decreasing the number of reactive encounters is clearly expressed. 

Alkanes.—Hydrogen Substitution. Whereas thermal hydrogen atoms react with alkanes exclusively by hydrogen abstraction, tritium atoms goierated by nuclear recoil also undergo the energetic substitution reaction (52) in high yield. ... 

The problem of localization of the A-factor receptor is now under investigation. The radioactive sample of the A-factor is used which has been prepsured by treatment of synthetjo A-factor with thermally excited tritium atoms. The level of A-factor binding by actinomycete cells was measured after a short-term treatment of 24 hr old mycelium no. 1439 with labelled A-factor. The same amount of A-factor was found to be bound to the cell (approximately 0.18 jug of the A-factor per 1 g of dry mycelium) after the treatment of the mycelium with rather different concentrations of the A-factor and subsequent careful washing. Distribution of the bound A-factor between different cell fractions was determined after destruction of washed mycelium. The A-factor content in cytoplasm was higher than in ribosomes, membranes and envelopes. The preliminary experiments of fractionation of cytoplasmic material showed that the A-factor was bound to proteins. 

Substitution of thermal and recoil tritium atoms into cyclo-octene shows differences from that into cyclohexene. ... 

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