RCOOCOR' name of this function group?
The name of the functional group RCOOCOR' is an acidic anhydride. It is formed by the removal of a water molecule from two carboxylic acid groups. The general formula is: $$
R−CO−O−CO−R^′
$$
Example- Acetic anhydride $$
CH_{3}CO−O−COCH_{3}
$$