O=c1c(Cc2c(O)ccc3ccccc23)nnc2sc(-c3nn4c(=O)c(Cc5c(O)ccc6ccccc56)nnc4s3)nn12
Hydrogen bond acceptor is the chemical compound which contains the lone electron pairs that participate in the hydrogen bond formation. This compound should contain a more electronegative atom (more electronegative than hydrogen) with lone electron pairs. Then it can attract protons from a donor. Moreover, the electronegative atoms usually involved in hydrogen bonding are oxygen, nitrogen and fluorine. How many hydrogen bond acceptors does the molecule contain?