A peak at 1700 cm$^{-1}$ in the IR spectrum is typically indicative of a carbonyl group C=O in the molecule. The carbonyl group can be found in various functional groups such as aldehydes, ketones, carboxylic acids, esters, and amides. To determine the specific structure of the molecule, more information from the IR spectrum, as well as other spectroscopic techniques like NMR, would be needed.