Chapter 14: Nuclear Magnetic Resonance Spectroscopy

Question: Label each statement as True or False.

a. When a nucleus is strongly shielded, the effective field is larger than the applied field and the absorption shifts downfield.

b. When a nucleus is strongly shielded, the effective field is smaller than the applied field and the absorption is shifted upfield.

c. A nucleus that is strongly deshielded requires a lower field strength for resonance.

d. A nucleus that is strongly shielded absorbs at a larger δ value.

Question: Rank each group of protons in order of increasing chemical shift.

a.

b.

Question: Which compounds give a ${}^{\mathbf{1}}\mathbf{H}$ NMR spectrum with two signals in a ratio of 2:3?

a.

b.

c.

d.

Question: Compound A exhibits two signals in its ${}^{\mathbf{1}}\mathbf{H}$ NMR spectrum at 2.64 and 3.69 ppm and the ratio of the absorbing signals is 2:3. Compound B exhibits two signals in its ${}^{\mathbf{1}}\mathbf{H}$ NMR spectrum at 2.09 and 4.27 ppm and the ratio of the absorbing signals is 3:2. Which compound corresponds to dimethyl succinate and which compound corresponds to ethylene diacetate?Question: Compound A exhibits two signals in its ${}^{\mathbf{1}}\mathbf{H}$ NMR spectrum at 2.64 and 3.69 ppm and the ratio of the absorbing signals is 2:3. Compound B exhibits two signals in its ${}^{\mathbf{1}}\mathbf{H}$ NMR spectrum at 2.09 and 4.27 ppm and the ratio of the absorbing signals is 3:2. Which compound corresponds to dimethyl succinate and which compound corresponds to ethylene diacetate?

Question: For each compound give the number of ${}^{\mathbf{1}}\mathbf{H}$NMR signals, and then determine how many peaks are present for each NMR signal.

a.

b.

c.

d.

Question: Sketch the NMR spectrum of$\mathbf{C}{\mathbf{H}}_{\mathbf{3}}\mathbf{C}{\mathbf{H}}_{\mathbf{2}}\mathbf{C}\mathbf{l}$, giving the approximate location of each NMR signal.

Question: How many peaks are present in the NMR signal of each labelled proton?

a.

b.

c.

d.

Question: Describe the ${}^{\mathbf{1}}\mathbf{H}$NMR spectrum of each compound. State how many NMR signals are present, the splitting pattern for each signal, and the approximate chemical shift.

a.

b.

c.

d.

Question: Draw a splitting diagram for ${\mathbf{H}}_{\mathbf{b}}$ in trans-1,3-dichloropropene, given that ${\mathbf{J}}_{\mathbf{a}\mathbf{b}}\mathbf{=}\mathbf{13}\mathbf{.1}\mathbf{H}\mathbf{z}$ and ${\mathbf{J}}_{\mathbf{b}\mathbf{c}}\mathbf{=}\mathbf{7}\mathbf{.2}\mathbf{H}\mathbf{z}$.

Question: The ${}^{\mathbf{1}}\mathbf{H}$ NMR spectrum of $\mathbf{C}{\mathbf{H}}_{\mathbf{3}}\mathbf{O}\mathbf{H}$ recorded on a 500 MHz NMR spectrometer consists of two signals, one due to the $\mathbf{C}{\mathbf{H}}_{\mathbf{3}}$ protons at 1715 Hz and one due to the OH proton at 1830 Hz, both measured downfield from TMS. (a) Calculate the chemical shift of each absorption. (b) Do the $\mathbf{C}{\mathbf{H}}_{\mathbf{3}}$ protons absorb upfield or downfield from the OH proton?