Question

Write detailed notes on the following terms:
(a) Strongly and weakly coupled NMR spectra

(b) Nuclear Overhauser Effect

Answer 1

(a) Strong and weak coupled NMR spectra can be understand by the concept of coupling constant. One proton on one carbon couple to the neighbouring proton on the adjacent carbon can be understand by the value of coupling constant. If value of coupling constant is more than coupling is better otherwise weaker if coupling constant is low.

For example, For cis alkent, proton has a coupling constant of 5 - 10 Hz whereas for trans isomer this value increases from 8 to 15 Hz.

(b) Nuclear overhauser effect: It is the transfer of nuclear spin from one spin to another via cross relaxation.