IUPAC name, phthalic anhydride Could someone help me please (preferably talk me through not just provide the answer) with the IUPAC name of phthalic anhydride?  I'm sorry for not posting attempts but I'm afraid I have absolutely no idea how to begin here...
Benzofuran is named by the position of the oxygen, hence 2-Benzofuran.  (below is 1-benzofuran)



The =O s are then added on the 1 and 3 carbons, hence, 1-3-dione  

Compare, cyclopentan-1,3-dione 



The end result is 

2-benzofuran-1,3-dione