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NOESY (Nuclear Overhauser Effect SpectroscopY) is a two-dimensional NMR experiment that shows which hydrogen nuclei in a molecule are close together in space, whether or not they are connected by chemical bonds. Each off-diagonal cross peak marks a pair of protons within roughly 4 to 5 Å of each other.
Short answer: what do you mean by NOESY?
NOESY is a 2D NMR experiment that maps through-space proximity between nuclei using the nuclear Overhauser effect (NOE). The Northwestern University IMSERC guide describes it as a simple way to obtain all NOE information in a molecule from a single experiment, without prior knowledge of the spectral assignment or molecular structure. It is the through-space counterpart of COSY, which maps through-bond coupling.
Definition and scope
The NOE depends on spatial proximity, not on through-bond J coupling. According to the Columbia University Chemistry NMR facility handout, the effect is seen for protons up to about 4 Å apart in small molecules, with an upper limit of about 5 Å in large molecules. In the NOESY pulse sequence (90°, t1, 90°, mixing time, 90°, detection), magnetization is transferred between spins during the mixing time by cross-relaxation or by chemical exchange (IMSERC).
The result is a square 2D spectrum with the ordinary 1D spectrum along the diagonal. A cross peak between two proton shifts means those protons are near each other in space. This is why NOESY is used for conformation and stereochemistry questions, and why it needs no prior assignment to be recorded. For the instrument itself, see the NMR spectrometer guide; for processing 2D data, see MestReNova.
NOESY vs COSY vs ROESY
What does a COSY NMR tell you?
COSY is homonuclear shift correlation: it transfers polarization between directly J-coupled spins, so it maps through-bond connectivity (IMSERC). NOESY answers a different question, which atoms are near each other in space, so the two are usually read together.
What is ROESY?
ROESY is the rotating-frame relative of NOESY. Its ROE is always positive, which matters for mid-sized molecules where the ordinary NOE can vanish (Columbia).
| Experiment | What the cross peak means | Source |
|---|---|---|
| COSY | Two spins are directly J-coupled (through-bond) | Northwestern IMSERC |
| NOESY | Two spins are close in space; also shows chemical exchange | Northwestern IMSERC; Columbia |
| ROESY | Same spatial question as NOESY; ROE always positive | Columbia |
Choosing the experiment by molecular size
The sign of the NOE depends on molecular weight (approximate values from the Columbia handout), and that drives the choice of experiment and the starting mixing time.
| Molecular size | NOE sign (approx.) | Usual choice | Mixing-time range (suggested start) |
|---|---|---|---|
| Small (MW below about 600) | Positive | 2D NOESY with zero-quantum suppression; 1D selective NOESY if concentrated and only one or two NOEs are wanted | 0.5 to 1 s (0.5 s) |
| Medium (about 700 to 1200) | Near zero | ROESY or EASY-ROESY | 0.1 to 0.5 s (0.25 s) |
| Large (above about 1200) | Negative | Usually NOESY; ROESY has less spin diffusion but is less sensitive and shows TOCSY artifacts | 0.05 to 0.2 s (0.1 s) |
Large molecules need short mixing times to limit spin diffusion. The same handout states that ROESY has only disadvantages for small molecules. A 2D experiment gives all NOEs at once; a 1D selective experiment gives them one at a time.
How to read a NOESY spectrum: a checklist
- Compare cross-peak phase with the diagonal. Per Columbia, ROESY and small-molecule NOESY cross peaks have opposite phase to the diagonal; large-molecule NOESY cross peaks have the same phase as the diagonal.
- Treat same-phase peaks in a small molecule with suspicion. Exchange peaks are always the same phase as the diagonal, because chemical exchange also produces cross peaks (the EXSY experiment studies this).
- Look for zero-quantum artifacts. In NOESY they appear as an up-down pattern between J-coupled protons.
- In ROESY, watch for TOCSY transfer. EASY-ROESY minimizes it.
Where it matters for lab staff: sample and run practicalities
From the Columbia facility guidance: dissolved oxygen and paramagnetic species such as Cu2+ reduce or quench the NOE. This is critical for small molecules and not critical for large ones. The facility recommends freeze-pump-thaw degassing (3 to 4 cycles) and notes that bubbling argon is not sufficient. Do not spin the sample, and control temperature on long runs. A normal 5 mm tube should not hold under about 500 µL; Shigemi tubes restrict the active volume for limited samples. Follow your own facility’s SOP for the specific spectrometer.
Common misunderstandings
- A NOESY cross peak is not evidence of a bond; it indicates proximity. Coupling through bonds is COSY territory.
- The NOE does not always have the same sign. Around 700 to 1200 it can be close to zero, which is why ROESY is preferred there.
- Not every cross peak is an NOE; exchange and zero-quantum peaks look similar but differ in phase or pattern.
FAQ
What do you mean by NOESY?
A 2D NMR experiment that detects through-space closeness (about 4 to 5 Å) between nuclei via the nuclear Overhauser effect. See the definition above.
What does a COSY NMR tell you?
Which spins are directly J-coupled, that is, through-bond connectivity.
Where is NOESY?
NOESY is not a place or a menu item but an experiment run on an NMR spectrometer. Facilities typically provide it as a standard 2D experiment, with 1D selective and ROESY variants.
What are two types of NMR?
The phrase is ambiguous. Within this topic, the useful split is 1D versus 2D experiments: a 1D selective NOESY gives one NOE at a time, while 2D NOESY gives all of them in one run (Columbia).
See also organic spectroscopy databases and how to read mass spectrometry for complementary structure-elucidation data.
Sources
- J. Decatur, “NOESY and ROESY,” v5.1, Columbia University Chemistry NMR Facility, 8 Aug 2018: nmr.chem.columbia.edu (read 2026-11-07).
- Northwestern University IMSERC, eNMR guide, NOESY and COSY pages: imserc.northwestern.edu (read 2026-11-07).
- Neuhaus D., Williamson M. P., The NOE in Structural and Conformational Analysis, 2nd ed., Wiley-VCH, 2000 (reference text cited by the Columbia handout).
