Please answer! If heroin is more closely related to morphine than oxycontin, how is oxy stronger? o.O?

All of the opiates are chemically similar, they all are used for the same general effect. Opana (Oxymorphone), Dilaudid (Hydromorphone) and Oxycontin (Oxycodone) are all semi synthetic opioids made specifically to be stronger then morphine and codeine by isolating & combining molecules etc. and so forth. I won't go into the molecular structure in depth, but the relatively minute differences between the substances are the cause of the varied strength. They all derive from the Opium poppy to begin with. It's the same reason why Morphine is stronger then codeine, despite them both being predominant alkaloids in the flower.