I have to say that I'm amazed at the equanimity that people are treating the 9, 25, 16a, 21 homophone. It only works if you're an Italian from Brooklyn being played by Nicholas Cage. That said, it's extremely funny, so I won't complain too loudly. Those two clues were my last in because, even though I had three of the four clues for a long time, I couldn't work out how they could go together. Sadly, 25,22 was the last of the four even though he is one of my favourites.
7d is fine as a compound, Brendan. I'm not a chemist, but you just need Wikipedia rather than Chambers.