Propose a structure for a compound A that has an infrared absorption at 1820 cm-1 and a

Question:

Propose a structure for a compound A that has an infrared absorption at 1820 cm-1 and a single proton NMR absorption at δ 1.5. Compound A reacts with water to give dimethylmalonic acid and with methanol to give the monomethyl ester of the same acid. (Compound A was unknown until its preparation in 1978 by chemists at the University of California, San Diego.)