Chapter 10.6, Problem 20E

(a)

Interpretation Introduction

Interpretation:The various resonances corresponding to ${}^1\text{H}$ NMR of hydrogen nuclei found in $\text{meso-stilbene}$ dibromide should be assigned.

Concept introduction:The scale used for the NMR spectrum is delta scale. $\text{δ}$ denotes parts per million units. The lower values of $\text{δ}$ denote upfield while higher values of $\text{δ}$ denote downfield region.Each peak in the NMR spectrum corresponds to distinct hydrogen.

The area within each peak corresponds to the number of equivalent protons found at that chemical shift values.

Spin-spin splitting is observed as a result of the interaction amongst non-equivalent NMR active nuclei. This is independent of the strength of the external magnetic field. The formula to calculate the number of peaks in the ${}^1\text{H}$ NMR spectra is as follows:

  $\text{Number of peaks}=N+1$

Where,

• $N$ is the number of equivalent protons on the adjacent carbon atoms.

Thus if a fragment is $-{\text{CH}}_{\text{2}}-{\text{CH}}_{\text{3}}-$ then it would show a three proton triplet due to ${\text{CH}}_{\text{3}}$ and a two proton quartet in accordance with $N+1$ the rule.

(b)

Interpretation Introduction

Interpretation: The various resonances corresponding to ${}^{13}\text{C}$ NMRofcarbon nuclei found in $\text{meso-stilbene}$ dibromide should be assigned.

Concept introduction: The scale used for the NMR spectrum is the delta scale. $\text{δ}$ denotes parts per million units. The lower values of $\text{δ}$ denote upfield while higher values of $\text{δ}$ denoting downfield region. Each peak in the NMR spectrum corresponds to distinct hydrogens.

Thus if a fragment is $-{\text{CH}}_{\text{2}}-{\text{CH}}_{\text{3}}-$ then it would show two carbon signals for each of carbon atoms.