COSY. Correlation Spectroscopy. Click on peak or more information. This experiment shows proton-proton correlation (which protons are coupled to which). Coupled protons are typically on adjacent carbons. The x and y axis are both 1-D proton spectra. Since the axies are identical, the 2D data is a symetric matrix. The diagonal is a 1-D spectrum and the off diagonal peaks (also called cross peaks), show which protons are coupled.