Question: acetaminophen is combined with phenylephrine in cold and flu formulations...
Acetaminophen is combined with phenylephrine in cold and flu formulations. Under physiological conditions (pH ~7) phenylephrine exists as a "zwitterion" (containing charged atoms that cancel each other, giving the compound a neutral net charge). Based on this information, and using your pKa table, draw the zwitterion form of this chemical?
The answer is listed here, and apparently the O that was deprotinated has a pka of 6.5. I'm not understanding why this oxygen has a pka of 6.5? I thought it had a pka of 10. Can someone please explain why oxygen has a pka of 6.5 in this problem?