Which part of dopamine molecule determines its pKa that is known to be 8.9ish..is it the NH2 attached to the ring structure? Thanks!!
I'm not exactly sure what you mean by this. The amine and phenol groups all contribute to the acid/base chemistry of dopamine.
A couple of things to get you started:
You say the pKa of dopamine is ~8.9. Can you draw (or describe) the precise species you think has this pKa, indicating any charges?
Hint: What percentage of acetic acid (pka = 4.
is protonated at pH 4.8?