Reactions of ^34mCl and ³⁸Cl Atoms Recoiling in Liquid Halobenzenes

Abstract

The reactions of radioactive chlorine atoms recoiling from two nuclear processes, "Cl(n, 2n)"'"a and "Cl(n, 7)"CI have been studied in different liquid halobenzenes. The ratio "Q-for-Cl vs.^'Cl-for-H yield for C^HjCl is dose-dependent, indicative for radiation-enhanced ^' Cl-for-Cl exchange. The Cl-for-Cl replacement yield is lowered on the addition of Ij, but much more for "CI than for It is suggested that the precursors to the exchange is a charge-transfer 7r-complex, rather than a a-complex. The fraction of the * Cl-for-Cl replacement yield not affected by Ij is ascribed to direct hot one-step processes. The behaviour of m-Cj H4 Clj is different to the extent that -as measured for 34 mQ _ thermal exchange seems to take place. Also, isomeric dichlorobenzenes irradiated in a mixture show differences among each other in exchange behaviour. Part of the unidentified products is attributed to an excited jr-complex subject to ring-opening and/or fragmentation. The ""'Cl vs."Cl isotope effect is not due to external radiation and is discussed in terms of differences in the recoil energy distribution and the life-time of lower levels of nuclear excitation.

Reactions of Recoil 38Cl Atoms with α-Chlorotoluenes

“…The yields are less than 1 % per H atom [8]. 4) Thermal '®Cl-for-Cl substitution yields are lower for monochlorotoluenes than for mono-and dichlorobenzenes due to the competitive abstraction of H from the CHa group which was also substantiated by addition experiments with I2 [9]. 5) The model proposed by KONTIS and URCH [12,13] is useful in the determination of the reactivity Parameters of recoil ^'Cl atoms in a variety of mixtures with chlorotoluenes [10,11] (KONTIS and GASPARAKIS [14] have recently extended this model to determine the cross-section parameters for the formation of dichlorobenzenes by measuring the individual product yields).…”

“…These studies were performed with the aim of gaining insight into the mechanisms of the hot and thermal substitution and abstraction processes as well as selectivity effects by measuring the total organic, substitution and Polymerie yields [3][4][5][6][7]. Chlorotoluenes, among the arenes, seem to provide valuable Information on these aspects and we have, therefore, undertaken a detailed investigation on the reactions of recoil "Cl atoms with these Compounds [8][9][10][11].…”

Recoil 38CI Reactions with Halobenzenes: Substituent Effects

“…These findings clearly demonstrated that the presence of a second chlorine at different positions in an aromatic compound plays a prominent role in the substitution processes. BRINKMAN and coworkers have found that in 1 : 1 : 1 mixtures of isomeric dichlorobenzenes [5] and in the respective chlorotoluenes [4], the ο: m : ρ substitution yields were almost statistical, whereas the distribution for thermal exchange was very selective, favouring the o-and p-isomers. They have recently extended their studies to different mixtures of isomeric C 6 H 4 C1X (X = F, CI, CH 3 , CF 3 ) compounds to obtain more information on aspects such as relative rates and selectivity for exchange [8].…”

Formation of Dichlorobenzenes 38Cl by Recoil in Systems with Chiorobenzene

“…Especially, httle is known about the reactions of recoil atoms, produced by radiative neutron capture, in such systems [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][18][19][20][21][22][23].…”