KEGG LIGAND

KEGG LIGAND is an alternative to the NCBI databases, covering the "molecular building blocks of life in the chemical space." Its interlinking is simpler and more up-front than NCBI's -- if not as complete. The Reaction database is easy to use. Compare diethylene glycol in NCBI and LIGAND.

Article
Susumu Gotoa Takaaki Nishioka, and Minoru Kanehisa.
LIGAND: chemical database of enzyme reactions.
Nucleic Acids Res. 2000 January 1; 28(1): 380–382.