No. You can, however, lawfully burn a copy of the song from your CD onto your computer. In legal lingo, that is "space shifting" which, even according to the recording industry attorneys, is lawful. But downloading a copy of the recording from someone else's library is not lawful. Others may, and do disagree, but that is my conclusion. In any event, why download the song when the technology to copy the song from your cd onto your computer is already on your computer and that process is, in fact, far easier and safer than downloading.
Your question is a bit unclear. If you mean can you take a cd you own and transfer the music on it from the CD onto your computer one time, yes that is legal. If you mean can you take the cd, trasnfer the music onto your computer and then make it available for download by others, the answer is no. If you mean does the fact that you own a copy of the cd permit you to download songs that are on the cd from other sources without paying for it, my answer would be no. Ownership of the cd is not license to download the song from somewhere else, though I admit that's a novel concept. I hope one of these three answers was what you were looking for.
My answer would still be "no." Owning one licensed version of a song does not give you license to download another copy of that song from an unlicensed source. It may take a little more time (though not much more) to upload your cd on to your computer and then download it onto your Iphone, but that's the most legal way you can do it.That would be the "space shifting" that Daniel is talking about. Otherwise, after anyone got caught illegally downloading songs, they would run out, obtain the cds and then claim a license.
I think that both Oscar and I understood the original question. You, however, seem not to like the answer. Oscar's follow-up answer is again correct, to wit:
Query: May I download a torrrent of that exact album from a file share?
Answer: The answer is still no.
Query: if I had my PC seized and every track on it although downloaded could also be found on a purchased produced cd in my physical library, have I committed a copyright infraction?
Answer: The answer is still yes.
You may lawfully rip a copy of song from a cd that you own onto your computer. You may not download that same song from a file sharing site onto your computer. That's the law, whether it makes sense to you or not. And, frankly, why on earth would you want to download a bootleg copy when you can lawfully rip a copy from your own cd?