Chemical exchange

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Contents 1 Chemical Exchange 2 Introduction 3 Fast Exchange 4 Intermediate Exchange 5 Slow Exhange 6 References

Chemical Exchange

Introduction

Chemical exchange for NMR processes can be classed into three major groups: fast exchange, intermediate exchange and slow exchange. In the equations below k is the exchange rate, and Ω (offset) (omega; majuscule ) is the difference of the rotating frame frequency (ω_rot.frame, omega ;minuscule) from the Larmor frequencey (ω₀). Then , Ω is given by the expression: [Ω = ω₀ − ω_rot.frame]. The units for the exchange rate and the units for the offset are the same and are in hertz or per second.

Fast Exchange

Fast exchange: k >>|Ω1-Ω2|-The exchange rate is much greater than the difference between resonance peak positions.

Intermediate Exchange

Intermediate exchange: k ~|Ω1-Ω2|-The exchange rate is approximately equal to the difference between resonance peak positions.

Slow Exhange

Slow exchange: k << |Ω1-Ω2|-The exchange rate is much less than the difference between resonance peak positions.

References

Keeler, J. (2005) Understanding NMR Spectroscopy, 3rd ed., Wiley.[1][2] 2) Center for Magnetic Resonance and Imaging [3]