The term cyclic hydrocarbon group having 5 or 6 carbon atoms in the ring is inclusive of cyclopentylidene, cyclopentenylidene, cyclopentadienylidene, cyclohexylidene, cyclohexenylidene, cyclohexadienylidene, and the like, and the corresponding cyclic hydrocarbons having substituents such as alkyl groups and hydrocarbon rings fused thereon to form radicals such as indenylidene, isoindenylidene, f