COMPUTER EXERCISES:
Computer Problem Set 2
The following questions refer to figure “8.36” (carvone).
1.
2.
3.
Determine the areas of the four groups of resonances in the spectrum; the resonances appearing in the range of 2.1–2.8 are to
be considered as one group. Using the “Landscape” mode, print a copy of the unexpanded spectrum that shows a listing of
the integrations. Ignore the peak near 7.3 as it is an impurity.
To the nearest 0.01 ppm, provide the chemical shift of each set of protons, writing these values by the corresponding
resonances on your printed spectrum. In the case of multiplets, the value should be at the center of the multiplet.
Based on chemical shifts, integrations, and multiplicities, assign the resonances associated with the protons labeled “a–d See
figure below),” and write these assignments on your printed spectrum by the peak(s) to which they correspond. Provide a
justification for each of your assignments. Be certain to specify what electronic factors help you to account for the large
difference in the chemical shifts of the two different types of vinylic protons in carvone. (Hint: Consider what effect
electronic delocalization has on the electron density near the vinylic proton on C(3) of the molecule.
a
CH3
c
O
H b
H
Hc
H c
H3C
a
CH2
d
The following questions refer to figure “10.35” (E-stilbene) and file “10.34” (E-stilbene)
4.
5.
6.
7.
In file “10.35”, determine the areas of the 4 groups of resonances in the spectrum.
Based on chemical shifts, integrations, and multiplicities, assign the resonances associated with the protons labeled “a–d (see
below),” and write these assignments on your printed spectrum by the peak(s) to which they correspond. Provide a
justification for each of your assignments. Be certain to specify what electronic factor(s) may account for the downfield shift
of the proton that appears at lowest field.
By referring to the 13C data in figure 10.35 and using the predicted chemical shifts from the ChemSketch program as a guide,
assign the 13C resonances to the carbon atoms responsible for them. Provide the answer on a molecular structure written on
the 1H NMR printout.
In the IR spectrum of E-stilbene (figure “10.34”) determine the absorption(s) consistent with the trans relationship of the
vinylic hydrogen atoms. Also explain the absence of a significant absorption in the range of 1600-1700 cm-1 which is
normally characteristic of alkenes.
H
A
H B
H
HC
H
D
The following questions refer to figure “8.28” (1-butanol) and figures “14.1” and “14.3” (1-butanol and 1-bromobutane).
For figure “8.28” determine the areas of the five groups of resonances in the spectrum (ignore the peaks near 7.2; the area of
the peak near 1.9 should be ~0.5, not the 0.1 that it reports).
9. To the nearest 0.01 ppm, provide the chemical shift of each set of protons, writing these values by the corresponding
resonances on your printed spectrum. In the case of multiplets, the value should be at the center of the multiplet.
10. Based on chemical shifts, integrations, and multiplicities, assign the resonances associated with the protons labeled “a–e (see
below),” and write these assignments on your printed spectrum by the peak(s) to which they correspond. Provide a
justification for each of your assignments.
11. By referring to the 13C data of figure 8.28 and using the predicted chemical shifts from the ChemSketch program as a guide,
assign the 13C resonances to the carbon atoms responsible for them. Provide the answer on a molecular structure written on
the 1H NMR printout. Discuss whether the presence of a hydroxyl group has the same general effect on 13C chemical shifts
as it does on 1H shifts.
12. Please explain the differences and similarities in the IR spectra of 1-bromobutane and 1-butanol in figures “14.1” and “14.3”.
8.
d
b
H3C
OH e
c
a
The following questions refer to figures “15.19” and “15.20” (bromobenzene)
13. For figure “15.20”, determine the areas of the 2 groups of resonances in the spectrum (ignore the peak near 1.6).
14. Based on chemical shifts, integrations, and multiplicities, assign the resonances associated with the protons labeled “a–b (see
below),” and write these assignments on your printed spectrum by the peak(s) to which they correspond. Provide a
justification for each of your assignments.
15. By referring to the 13C data of figure 15.20 and using the predicted chemical shifts from the ChemSketch program as a guide,
assign the 13C resonances to the carbon atoms responsible for them. Provide the answer on a molecular structure written on
the 1H NMR printout.
16. For figure “15.19” specify the absorption associated with the π-bonds of the aromatic ring. Indicate with what structural
feature the strong absorptions at 740 and 690 cm-1 are associated.
Br
Ha
H b
H
b