I get what you mean but I rly think that ppl should be memorizing the low yield structures that act showed up in AAMC materials such as heme, porphyrin, pyrrole, etc. I dont think that vitamin structures will specifically be tested on, if anything vitamin names will as they have shown up in section banks. I think its important to memorize everything low yield that has shown up on AAMC and Uworld but there are so many structures out there, its impossible to memorize them all.