Wikipedia
Trimethylenemethane
Trimethylenemethane (often abbreviated TMM) is a chemical compound with formula . It is a neutral free molecule with two unsatisfied valence bonds, and is therefore a highly reactive free radical. Formally, it can be viewed as an isobutylene molecule with two hydrogen atoms removed from the terminal methyl groups.
Trimethylenemethane was first conjectured to be an intermediate in some chemical reactions. It was observed in 1966 by Paul Dowd at very low temperature.
Paul Dowd (1972), Trimethylenemethane. Accounts of Chemical Research, volume 5, issue 7, pages 242–248.