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Chemistry · Glossary

What is COSY, HSQC, HMBC, NOESY?

Also known as: COSY · HSQC · HMBC · NOESY

Definition 8.18 University Chemistry — Year 3 · Chapter 8 — NMR in Depth: Pulses, Relaxation and 2D

COSY (correlation spectroscopy) correlates protons coupled to each other, usually through three bonds (H–C–C–H). HSQC (heteronuclear single-quantum coherence) correlates each carbon with the protons directly bonded to it. HMBC (heteronuclear multiple-bond correlation) correlates carbons with protons two or three bonds away, across quaternary carbons and heteroatoms. NOESY correlates protons close in space through the nuclear Overhauser effect.

Pulse sequences (time to the right; filled boxes: pulses, labelled with their flip angles in degrees; blue: the recorded signal). The spin echo peaks at 2 after the first pulse.
Pulse sequences (time to the right; filled boxes: pulses, labelled with their flip angles in degrees; blue: the recorded signal). The spin echo peaks at 2τ2\tau after the first pulse.
Two-dimensional spectra of ethyl butanoate, CH3CH2CH2COOCH2CH3, drawn at its measured shifts. COSY: black, diagonal peaks; red, cross peaks between protons on neighbouring carbons — two spin systems, ethyl and propyl, with no cross peak across the ester oxygen. Right: HSQC peaks (squares) join each proton to its carbon; HMBC peaks (circles) show the OCH_2 protons (4.13\, ppm) and the CH_2C=O protons (2.28\, ppm) both reaching the carbonyl carbon at 173.6\, ppm.
Two-dimensional spectra of ethyl butanoate, CHX3CHX2CHX2COOCHX2CHX3\ce{CH3CH2CH2COOCH2CH3}, drawn at its measured shifts. COSY: black, diagonal peaks; red, cross peaks between protons on neighbouring carbons — two spin systems, ethyl and propyl, with no cross peak across the ester oxygen. Right: HSQC peaks (squares) join each proton to its carbon; HMBC peaks (circles) show the OCH2_2 protons (4.13 ppm4.13\,\mathrm{ppm}) and the CH2_2C=O protons (2.28 ppm2.28\,\mathrm{ppm}) both reaching the carbonyl carbon at 173.6 ppm173.6\,\mathrm{ppm}.
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