The COSY NMR experiment - Who is your neighbor? | nmr.academy 

Beginner NMR course for students available at
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COSY (Correlation Spectroscopy) is a two-dimensional Nuclear Magnetic Resonance (NMR) technique that is used to study the correlations between hydrogen atoms in a molecule. It provides detailed information about the connectivity of protons in a molecule, revealing the number of neighboring protons and their chemical shift values. The technique is extremely useful, when there is extensive signal overlap in the one-dimensional spectrum.
More about COSY (with some nice eamples) in the video.
What information COSY provides 0:00
The COSY pulse sequence 1:52
Example 1: Ethyl acetate 3:48
Example 2: Ethyl propionate 6:14
Example 3: 4-hydroxybutanal 8:13