llocarbon obtainable by reacting an alkyl etal (such as a dialkyl zinc or a trialkyl aluminium compound) with a methane derivative of formula CHR 3 X'X (wherein R 3 is as defined above and X' and X are, independently, a leaving group) has a moiety that can be represented as 3 3 '-CHR L (wherein M' is a metal, such as zinc or aluminium, R is as defined above, and L is a leaving group).