Chapter 16, Problem 16.20P

Interpretation Introduction

(a)

Interpretation:

The number of signals that would be generated in the ${}^{\text{1}}\text{H}$ NMR spectrum for the given molecule with splitting pattern for each signal is to be determined.

Concept introduction:

In a ${}^{\text{1}}\text{H}$ NMR the number of signals is equal to the number of types of protons in the molecule. The chemically equivalent protons absorb at the same magnetic field and produce one signal, whereas the chemically non equivalent or distinct protons absorb at a different magnetic field to produce different signals. The separation of NMR peaks into number of smaller peaks is called as splitting of NMR peaks. It occurs due to the effect of the magnetic field of one nucleus on other adjacent or neighboring nuclei. This means the coupling of the spin states of one nucleus with the spin states of adjacent or neighboring nuclei, thus called spin-spin coupling. Therefore, the splitting is caused by the spin-spin coupling. The chemically distinct protons are called non-equivalent protons and have different chemical shift. The non-equivalent protons can couple each other’s signal whereas equivalent protons do not. The multiplicity of the peak depends on the number of neighboring protons, which can be determined by $\text{(N+1)}$ rule, where N is the number of neighboring protons. If the signal for a particular proton appears as singlet, it indicates that the proton has no neighboring protons.

Answer to Problem 16.20P

The number of signals with their splitting patterns in the given molecule is indicated as

Explanation of Solution

The structure of the given compound is

The compound has three chemically distinct protons indicated as $\text{A,}\text{B}$, and $\text{C}$, so there must be three signals in ${}^{\text{1}}\text{H}$ NMR spectrum.

The protons $\text{A}$ and $\text{B}$ are adjacent to each other. Each proton $\text{A}$ couples with one proton $\text{B}$, and according to $\text{(}N\text{+1)}$ rule, where $N\text{= 1}$ and $N\text{+1= 2}$, the signal for protons $\text{A}$ appears as doublet. Each proton $\text{B}$ couples with three proton $\text{A}$, and according to $\text{(}N\text{+1)}$ rule, where $N\text{= 3}$ and $N+1=4$, the signal for protons $\text{B}$ appears as quartet. Proton $\text{C}$ has no adjacent protons; thus its singal does not split and appears as singlet.

Splitting of each type of proton is shown below:

Conclusion

The splitting pattern for each type of proton signal in the given molecule is determined based on their respective number of neighboring protons.

Interpretation Introduction

(b)

Interpretation:

The number of signals that would be generated in the ${}^{\text{1}}\text{H}$ NMR spectrum for the given molecule with splitting pattern for each signal is to be determined.

Concept introduction:

In a ${}^{\text{1}}\text{H}$ NMR the number of signals is equal to the number of types of protons in the molecule. The chemically equivalent protons absorb at the same magnetic field and produce one signal, whereas the chemically non equivalent or distinct protons absorb at a different magnetic field to produce different signals. The separation of NMR peaks into number of smaller peaks is called as splitting of NMR peaks. It occurs due to the effect of the magnetic field of one nucleus on other adjacent or neighboring nuclei. This means the coupling of the spin states of one nucleus with the spin states of adjacent or neighboring nuclei, thus called spin-spin coupling. Therefore, the splitting is caused by the spin-spin coupling. The chemically distinct protons are called non-equivalent protons and have different chemical shift. The non-equivalent protons can couple each other’s signal whereas equivalent protons do not. The multiplicity of the peak depends on the number of neighboring protons, which can be determined by $\text{(N+1)}$ rule, where N is the number of neighboring protons. If the signal for a particular proton appears as singlet, it indicates that the proton has no neighboring protons.

Answer to Problem 16.20P

The number of signals with their splitting patterns in the given molecule is indicated as

Explanation of Solution

The structure of the given compound is

The compound has two chemically distinct protons indicated as $\text{A}$ and $\text{B}$, so there must be two signals in ${}^{\text{1}}\text{H}$ NMR spectrum.

Protons $\text{A}$ and $\text{B}$ are adjacent to each other. Each proton $\text{A}$ couples with two proton $\text{B}$, and according to $\text{(}N\text{+1)}$ rule, where $N\text{= 2}$ and $N\text{+ 1 = 3}$, the signal for protons $\text{A}$ appears as triplet. Each proton $\text{B}$ couples with one proton $\text{A}$, and according to $\text{(}N\text{+1)}$ rule, where $N\text{= 1}$ and $N+1=2$, the signal for protons $\text{B}$ appears as doublet. Splitting of each type of proton is shown below:

Conclusion

The splitting pattern for each type of proton signal in the given molecule is determined based on their respective number of neighboring protons.

Interpretation Introduction

(c)

Interpretation:

The number of signals that would be generated in the ${}^{\text{1}}\text{H}$ NMR spectrum for the given molecule with splitting pattern for each signal is to be determined.

Concept introduction:

In a ${}^{\text{1}}\text{H}$ NMR the number of signals is equal to the number of types of protons in the molecule. The chemically equivalent protons absorb at the same magnetic field and produce one signal, whereas the chemically non equivalent or distinct protons absorb at a different magnetic field to produce different signals. The separation of NMR peaks into number of smaller peaks is called as splitting of NMR peaks. It occurs due to the effect of the magnetic field of one nucleus on other adjacent or neighboring nuclei. This means the coupling of the spin states of one nucleus with the spin states of adjacent or neighboring nuclei, thus called spin-spin coupling. Therefore, the splitting is caused by the spin-spin coupling. The chemically distinct protons are called non-equivalent protons and have different chemical shift. The non-equivalent protons can couple each other’s signal whereas equivalent protons do not. The multiplicity of the peak depends on the number of neighboring protons, which can be determined by $\text{(N+1)}$ rule, where N is the number of neighboring protons. If the signal for a particular proton appears as singlet, it indicates that the proton has no neighboring protons.

Answer to Problem 16.20P

The number of signals with their splitting patterns in the given molecule is indicated as

Explanation of Solution

The structure of the given compound is

The compound has three chemically distinct protons indicated as $\text{A,}\text{B}$, and $\text{C}$, so there must be three signals in ${}^{\text{1}}\text{H}$ NMR spectrum.

Protons $\text{A}$ and $\text{B}$ are adjacent to each other. Each proton $\text{A}$ couples with two proton $\text{B}$, and according to $\text{(}N\text{+1)}$ rule, where $N\text{= 2}$ and $N\text{+ 1 = 3}$, the signal for protons $\text{A}$ appears as triplet. Each proton $\text{B}$ couples with one proton $\text{A}$, and according to $\text{(}N\text{+1)}$ rule, where $N\text{= 2}$ and $N+1=3$, the signal for protons $\text{B}$ appears as triplet. The protons $\text{C}$ has no adjacent protons; thus its singal does not split and appears as singlet. The splitting of each type of proton is shown below:

Conclusion

The splitting pattern for each type of proton signal in the given molecule is determined based on their respective number of neighboring protons.

Interpretation Introduction

(d)

Interpretation:

The number of signals that would be generated in the ${}^{\text{1}}\text{H}$ NMR spectrum for the given molecule with splitting pattern for each signal is to be determined.

Concept introduction:

In a ${}^{\text{1}}\text{H}$ NMR the number of signals is equal to the number of types of protons in the molecule. The chemically equivalent protons absorb at the same magnetic field and produce one signal, whereas the chemically non equivalent or distinct protons absorb at a different magnetic field to produce different signals. The separation of NMR peaks into number of smaller peaks is called as splitting of NMR peaks. It occurs due to the effect of the magnetic field of one nucleus on other adjacent or neighboring nuclei. This means the coupling of the spin states of one nucleus with the spin states of adjacent or neighboring nuclei, thus called spin-spin coupling. Therefore, the splitting is caused by the spin-spin coupling. The chemically distinct protons are called non-equivalent protons and have different chemical shift. The non-equivalent protons can couple each other’s signal whereas equivalent protons do not. The multiplicity of the peak depends on the number of neighboring protons, which can be determined by $\text{(N+1)}$ rule, where N is the number of neighboring protons. If the signal for a particular proton appears as singlet, it indicates that the proton has no neighboring protons.

Answer to Problem 16.20P

The number of signals with their splitting patterns in the given molecule is indicated as

Explanation of Solution

The structure of the given compound is

The compound has only one type of protons indicated, so there must be only one signal in ${}^{\text{1}}\text{H}$ NMR spectrum.

As all protons are chemically equivalent, they do not couple with each other’s signal and appear as singlet.

Conclusion

The splitting pattern for proton signal in the given molecule is determined based on their respective number of neighboring protons.