kahevalentsed rühmad R2C=, mis tekivad kahe vesinikuaatomi eemaldamisel ühe ja sama süsinikuaatomi juurest, kusjuures moodustub vaba kaksikside
divalent groups, R2C=, formed by removing two hydrogen atoms from the same carbon atom of a hydrocarbon, the free valencies of which are engaged in a double bond
