Final answer:
The chemical properties of heroin make it more nonpolar than morphine and oxycodone, allowing it to more easily cross the blood-brain barrier.
Step-by-step explanation:
Heroin vs Morphine and Oxycodone
Heroin is less soluble in water and more similar to oil than morphine and oxycodone. This means that substances that are more oil soluble are able to pass through the blood-brain barrier (BBB) more easily.
Unlike morphine and oxycodone, heroin does not have hydroxyl (OH) groups with which to form hydrogen bonds. This makes heroin more nonpolar than morphine and oxycodone.
Because the BBB is more like oil than water, heroin is able to cross it more easily than morphine and oxycodone.