1. Purpose

The transverse or spin–spin relaxation time T₂ determines the decay of the x,y magnetization and is related to the line-width. It must be clearly distinguished from the longitudinal or spin–lattice relaxation time T₁ (Exp. 6.1) and can be measured separately. Although there is hardly a direct relationship between the spin–spin relaxation time and the structure of molecules, a knowledge of its value is important for planning dynamic NMR experiments, investigations on spin diffusion, and generally for devising new pulse sequences, because their evolution periods must not significantly exceed T₂. In the extreme narrowing limit the relationship T₁ = T₂ usually holds. The spin-echo method for measuring T₂ is described here using CHCl₃ as an example.

2. Literature

S. Meiboom, D. Gill, Rev. Sci. Instrum. 1958, 29, 688–691.
M. L. Martin, J.-J. Delpuech, G. J. Martin, Practical NMR Spectroscopy, Heyden, London, 1980, 280–287.
R. Freeman, A Handbook of Nuclear Magnetic Resonance, Longman Scientific Technical, Harlow, 1987, 48, 116–117.
S. W. Homans, A Dictionary of Concepts in NMR, Revised Edition, Clarendon Press, Oxford, 1993, 310–314.
W. R. Carper, Concepts Magn. Reson. 1999, 11, 51–60.

3. Pulse Scheme and Phase Cycle

CPMG pulse sequence for proton spin–spin relaxation measurement

4. Acquisition

Time requirement: 0.5 h

Sample: 3% CHCl₃ in [D₆]acetone, degassed and sealed.