Thanks to tetrahedral carbon the number of possible molecules that can exist seems infinite. Any child can take a piece of paper and draw a completely unique molecule on it and name it after itself, sticking to the basic rules of valence, multiple bonding and some common sense with regard to cluttering. Synthesising the molecule in question is of course another matter. Can a molecule therefore be rare? No. Yang Xiao et al. in a recent publication however seem to differ, they titled it "Regioselective Electrosynthesis of Rare 1,2,3,16-Functionalized Fullerene Derivatives". Nothing wrong with the publication itself: a fullerenoindole (itself the adduct of fullerene and an aniline) was electroreduced and the dianion subjected to benzyl bromide. The benzyl group ended up exclusively at the 16-position and a proton (derived from stray water) at the 3-position. Congratulations on the regioselectivity achieved but obtaining a "rare" molecule by decorating a fullerene with any number of substituents is not an accomplishment. If the reaction was not regioselective at all you would have ended up with many more "rare" molecules. Let's reserve rarity to animals uncovered by biologists in remote parts of the world or a Da Vinci painting. "Rare" has no business in chemistry.