Chapter 16, Problem 16.13YT

Interpretation Introduction

Interpretation:

In the given ${}^{\text{1}}\text{H NMR }$ spectrum, the pair of signals that represents coupled protons 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.