related to e-cigs. Diacetyl Warning http://www.reddit.com/r/electronic_cigarette/comments/g225g/diacetyl_warning/ What is Diacetyl? Diacetyl  ( IUPAC   systematic name :  butanedione  or  2,3-butanedione ) is a natural byproduct of  fermentation . It is a  vicinal   diketone  (two C=O groups, side-by-side) with the  molecular formula  C 4 H 6 O 2 . Diacetyl occurs naturally