Recoil chlorine ¡Chlorotoluenes /Hot atom chemistry /Ipso attack AbstractThe chemical reactions of recoil 38 C1 atoms have been studied in liquid ortho, meta and para chlorotoluenes and in a 1 :1:1 mixture. In the pure liquids, the total organic yield is less in meta isomer compared to ortho and para isomers and is mainly due to a lower 3 * Cl-for-Cl substitution yield. In systems scavenged with 2 mol % I,, these substitution yields are about same for each of the three isomers. In a 1 :1 :1 mixture of the o : m : ρ isomers, containing 2 mol % I 2 , the ratios of the (hot) 38 Cl-for-Cl substitution yields are close to statistical. The distribution for thermal exchange reactions is however, selective. The 3, Cl-for-H substitution yield is less than 1 % per Η atom-aromatic and methylic-and is scavenger independent. The 3, Cl-for-CH 3 substitution yield is also about 1 %, whereas in a 1 :1 :1 mixture the o : m ; ρ ratio is not far from statistical.

The products of the reaction of CHgCOOF and F2 with uracil and cytosine dissolved in acetic acid and water were studied by using 18F as a tracer. Apart from 5-fluorouracil (2) and the 5,5-difluoro adducts 5a and 5b, the NMR spectra of the crude reaction mixture showed the presence of two geometric isomers of both 5fluoro-6-acetoxy-5,6-dihydrouracil (3a, 4a) and 5-fluoro-6-hydroxy-5,6-dihydrouracil (3b, 4b). In the fluorination of cytosine, corresponding products were observed with the exception of the acetoxy adducts. For both reagents and for both substrates a radical-cation mechanism is proposed. The observed conversions of the acetoxy adducts of uracil are explained by an acylimine (iii) as an intermediary.

There is an increasing interest in fluorinated aromatic compounds especially from a pharmaceutical point of view.1 However, problems regarding the introduction of fluorine into organic molecules differ considerably from those concerning other halogen atoms. Only a few practical

The reactions of recoil 11C atoms with liquid C6H6 result in the production of 11C‐labelled cycloheptatriene (CHT) and toluene in equal amounts of approximately 3%. From the effect of O2 on the product yields it is concluded that recoil labelling proceeds via both singlet and triplet 11CH2 intermediates, whereas 11CH may also contribute specifically to the formation of C6H5CH3. Addition of H2S increases the [11C]C6H5CH3 yield by ca. 5%, probably due to reactions of triplet phenyl‐carbene (C6H5CH). The reactions of singlet CH2, produced via the photolysis of CH2N2, with liquid C6H6 were also investigated in the presence of N2, O2 and I2.

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