alkylidene groups
The divalent groups formed from @A00222@ by removal of two hydrogen atoms from the same carbon atom, the free valencies of which are part of a double bond, e.g.
PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1314 [Terms] [Paper]