So I'm supposed to be getting a LOR from a chem professor I had in the past. He's being unresponsive at the moment. Another professor that I TA'd for said he'd be willing to write one for me if the chem professor letter falls through. He knows me well but I didn't personally have him as a teacher. Are there any schools in specific that ya'll know of that require you to have actually had the letter writer as your professor? Any feedback would be awesome!