The TOCSY (TOtal Correlation SpectroscopY) sequence is a homonuclear experiment which produces a COSY-like plot. A COSY will give correlations between protons that are coupled to one another. A TOCSY, on the other hand, will give correlations between all protons in a given spin system. Below is the TOCSY spectrum of 3-heptanone. There are two 1H spin systems; the protons on carbons 1 and 2 and the protons on carbons 4, 5, 6 and 7. The protons on carbons 1 and 2 have a correlation as they would in a COSY spectrum. The protons on carbons 4, 5, 6 and 7 are all correlated to one another whereas in a COSY spectrum, the main correlations would be between 4-5, 5-6 and 6-7 but not, for example, between the protons on carbons 4 and 7.