Songs won't sync to iPhone but play in iTunes
I have searched the discussion boards endlessly but can't find anything that solves my issue so I am posting my own thread. The vast majority of my music is purchased from the iTunes store and I have never had a problem syncing from iTunes on my MacBook to my iPhone 5. However, I have some music (mp3 files) that were acquired elsewhere and although the songs play in iTunes, they will not sync to my iPhone. The songs/playlists don't even show up on the phone and I cannot figure out why. Please help.
Note: I am running the most recent version of both iOS and iTunes.
Note: I have tried converting a song from mp3 to ACC and AIFF files
iPhone 5