Chapter 16, Problem 16.12YT

Interpretation Introduction

Interpretation:

In Figure $\text{16-23}$, do the coupling constants suggest that protons B and C are coupled? Whether the answer agree with the molecule’s structure is to be determined.

Concept introduction:

The signals in an NMR spectrum tend to be better resolved as the magnet of the spectrometer becomes more powerful. This is true primarily because the magnetic fields that cause signal splitting, that is, those produced by the various spin combinations of nearby nuclei, are independent of the ${\text{B}}_{\text{ext}}$. Therefore, regardless of the strength of ${\text{B}}_{\text{ext}}$, the frequency difference between peaks of a split signal, called the coupling constant (J), remains unchanged. By contrast, for an unsplit signal, increasing ${\text{B}}_{\text{ext}}$ causes an increase in ${\text{ΔE}}_{\text{spin}}$ and, hence, an increase in the signal frequency.