Wikipedia
Hydrogenacetylenedicarboxylate
Hydrogenacetylenedicarboxylate (often abbreviated as Hadc or HADC) is a monovalent anion with the formula CHO or HOC-C≡C-CO. The anion can be derived from acetylenedicarboxylic acid by removal of a single proton, or from the acetylenedicarboxylate dianion by addition of a proton.
The name is also used for any salt of this anion; which may also be called acid, hydrogen, or monobasic acetylenedicarboxylate.
The parent acid was synthetized by E. Bandrowski in 1877. Salts of this anion are of interest in crystallography because they contain unusually short and strong hydrogen bonds.