Q.3. (b) Explain the significance of magnitude of “J” constant in structure elucidations.
Ans.3. (b) Coupling constant: The distance between the centers of the two adjacent peaks in a multiplet is usually constant and is usually called the coupling constant. The value of the coupling constant is independent of the external field. It is measured in Hertz (Hz) or in cps (cycles per second). It is denoted by the letter J.
Significance of J constantin structure elucidations
The value of J has various significances such as from the constant value of J, we came to know that the multiplets formed are of symmetrical nature. It has been noted that the departure from the symmetrical nature of the multiplet results when the absorption positions (chemical shifts) of the interacting groups are close enough.
Coupling constants are a measure of the effectiveness of spin-spin coupling and have been very useful in getting exact information from PMR spectra of complex molecular structures.
The magnitude of J depends to a large extent on the number of bonds intervening between the two atoms or groups of atoms that interact.
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