Question

Describe (using words and diagrams) how an NMR signal is generated as a nuclear spin relaxes. Explain the result of the excitation-relaxation cycle; show what happens with the progression of time. Explain how we get a peak from the raw data.

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Answer 1

Subatomic particles like electron,proton and neutron can be imagined as spinning on their axes.

If the number of neutrons and the number of protons are both even,then the nucleus has no spin.

If the number of neutrons plus the number of protons is odd,then the nucleus has a half integer spin.

If the number of neutrons and the number of protons are both odd,then the nucleus has an integer spin.

Apphed maanetic NO red tield Ene 2.

Relaxation refers to the phenomenon of nuclei returning to their thermodynamically stable states after being excited to higher energy levels.The two types of relaxation are spin lattice relaxation(T1) and spin spin relaxation (T2).

Enen

Spin lattice relaxation(T1) -T1 is the time it takes for the 37% of bulk magnetization to recovery along Z-axis from the X-Y plane.The more efficient the relaxation process,the smaller relaxation time value we get.

Spin spin relaxation(T2)- T2 is the time it takes for the spins to lose coherence with one another.T2 can either be shorter or equal to T1.

By integration,we get the peaks from raw data.Integration is the measurement of peak areas on the NMR spectrum.It corresponds to the amount of energy absorbed or released by all nuclei participating in chemical shift during the nuclear flip process