無機物理方法（核磁共振部分）. The Physical Methods in Inorganic Chemistry (Fall Term, 2004) (Fall Term, 2005) Department of Chemistry National Sun Yat-sen University. Chapter 4. Chapter 4. 90 o pulse width T 1 measurement T 2 measurement Chemical exchange. π. π /2. Fine Tuning until t π.
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90o pulse width= tπ/2
Any degree (n)-pulse = tπ*n/180.
Introduces observable contributions to signal decay:
τ1 = τ2
τ1 = T2
How far between two nuclei
How fast the molecule tumbles.
to the z axis, an oscillating field (oscillating
at the Larmor frequency of the transition)
that is orthogonal to the Zeeman field is
required. The source of these additional
fields is easy to see, the other nuclei which
have magnetic moments nearby. Thus, the
dipole-dipole interaction can actually
provide a mechanism for relaxation.
In the extreme narrowing limit (very fast motion and very short correlation time), the following holds.
Clearly, motion is restricted near the -OH end of the molecule (presumably
due to hydrogen bonding). As a result, these protons have relatively shorter
relaxation times (or faster relaxation rates) as the motions get slower and
approach the Larmor frequency.
some of the carbons in phenol. The relaxation time of the C directly
attached to the -OH group illustrates the importance of nearby protons
in the relaxation of C spins. Since this C is not directly attached to any
proton, its relaxation time is appreciable long. The anisotropic motion
of the ring (it prefers rotation about the axis that contains -OH) leads to
appreciably longer relaxation times for the C's that do not lie on this
(If d1 is long enough)
(If d1 is not long enough)The effect of T1 on the setting of recycle delay (d1)
T1, T2 and K are just a small tip of the iceberg of relaxation/exchange rates.