What is EXSY?
Abbreviation for EXchange SpectroscopY, a technique in NMR measurements. Another name for NOESY. The pulse sequences are identical to NOESY.[1,2] Since correlated signals also appear between chemically exchanged 1H in the NOESY measurement, it is sometimes called EXSY to avoid confusion when the purpose of the measurement is to detect chemical exchange.
By measurement, the rate of chemical exchanges can be determined.
Chemical exchanges include
- conformational change (e.g., rotation, flip)
- ligand exchange of metal complexes
Example
Diastereomers of [Ru(OH){(S,S)-Pfbsdpen}(η6 -hmb)] (Ru-R and Ru-S).[3]
Two diastereomers of ruthenium hydroxide, Ru-R and Ru-S, are in equilibrium with each other. Cross peaks in the 19F NMR EXSY of this mixture indicate the chemical exchange between these species.
Phase-sensitive 2D 19F–19F EXSY NMR spectrum (376.17 MHz, 193K, CD2Cl2, τm = 0.50 s) of the Ru complex in the presence of ~10 eq. of water (28% aqueous ammonia solution) at –80 ºC. The figure and chart are cited from the reference.[3]
References and Related Links
- JEOL website: Study of Chemical Exchange by NMR
- NMR Facility blog of University of Ottawa
-
Pavel A Dub, Hui Wang, Asuka Matsunami, Ilya D Gridnev, Shigeki Kuwata, Takao Ikariya, C–F Bond Breaking through Aromatic Nucleophilic Substitution with a Hydroxo Ligand Mediated via Water Bifunctional Activation, Bull. Chem. Soc. Jpn., 2013, 86, 557–568. https://doi.org/10.1246/bcsj.20120359