[en] In the recoil system ¹¹C+C₆H₆ the two primary products are ¹¹CH and ¹¹C₇H₆. These intermediates are formed by ¹¹C-insertion in a C-H bond and by π-addition, respectively. The - excited - carbenes ¹¹C₇H₆ are produced with a probability of about 70%, and are to a great extent responsible for the formation of polymers. Conspicuously, polymers heavier than tetramers were not observed. Secondary intermediates ¹¹C₇H₇ and ¹¹C₁₂H₁₁ react with radicals produced in the spur of the ¹¹C recoil particle to produce the trimers and tetramers. Thermalized carbenes ¹¹C₇H₆ give rise to dimers. (orig.)

[en] A comparative study has been made of the reactions of recoil ¹¹C atoms with c-C₆H₁₂, C₆H₆ and C₆ (CH₃)₆. Use was made of group separations of labelled recoil products by HPLC techniques. Reaction mechanisms are discussed on the basis of primary reactions of ¹¹C atoms: 1,H-abstraction leading to ¹¹CH; 2, insertion into a C-H bond, leading to an excited carbene that can decompose or isomerize to a stable monomeric compound. Thermal singlet carbenes can also insert into the C-H bond of another molecule (yielding dimeric compounds) whereas in the case of C₆H₆, a triplet carbene can add to the aromatic ring (leading to the formation of higher polymers); and 3, addition to the aromatic ring of C₆H₆ can also lead to an excited carbene, but such a process is thought to be sterically hindered in the case of C₆(CH₃)₆. (author)