Chapter 14, Problem 78P

(a)

Interpretation Introduction

Interpretation:

Number of signals expected in each of the following compounds in ${}^{\text{1}}\text{H}\text{NMR}$ spectrum has to be determined.

Concept introduction:

The number of signals in ${}^{\text{1}}\text{H}\text{NMR}$ is equal to the number of chemically non-equivalent protons. P-The protons in the different chemical environment are called chemically non-equivalent protons and the protons in the same chemical environment are called chemically equivalent protons.

For each set of chemically equivalent protons, there will be one signal.  For example, the ${}^{\text{1}}\text{H}\text{NMR}$ spectrum of ethanol $\left(\text{C}\underset{\text{a}}{{\text{H}}_{\text{3}}}-\text{C}\underset{\text{b}}{{\text{H}}_{\text{2}}}-\text{O}\underset{\text{c}}{\text{H}}\right)$ will show 3 signals because there are 3 set of chemically equivalent protons labelled as a, b and c.

(b)

Interpretation Introduction

Interpretation:

Number of signals expected in each of the following compounds in ${}^{\text{13}}\text{C NMR}$ spectrum has to be determined.

Concept introduction:

The signals in the ${}^{\text{13}}\text{C NMR}$ spectrum of a compound are proportional to the number of carbons that are present in the different environment within the molecule.  The carbon which is present in the electron-rich environment shows a signal at a lower frequency and vice-versa.  Therefore, the carbons that are present nearest to the electron-withdrawing groups produce a high-frequency signal.