I have a new Macbook pro. I downloaded all previous Itunes purchases and then sync my IPhone. The New song that I purchased today appear on the IPhone however it will not play. How do I fix the issue with my IPhone?

Hey Etti101,

I'd start off your troubleshooting process by deleting and redownloading the songs:

If iTunes in the Cloud is available in your country, try the following steps to resolve the issue:

1. Delete the purchased song that is exhibiting the problem from your iTunes library.
2. Click on the Purchased link in the iTunes Store to view your previously purchased music.
3. Download your previously purchased song from this list.

via: Songs in iTunes may not play back completely

http://support.apple.com/kb/TS4357

Regards,

Delgadoh