Two-dimensional NMR (2D-NMR) techniques such as COSY and HETCOR provide additional structural information about molecules beyond what can be learned from one-dimensional NMR. COSY identifies protons that are spin-coupled to each other, while HETCOR connects carbon signals to the protons bonded to those carbons. These 2D NMR techniques simplify analysis of complex molecules like proteins by separating overlapping signals.