Physical Chemistry , 1st ed.

16.25.Calculate the strength of the magnetic field necessary

to observe NMR signals of the NMR-active nuclei from exer-

cise 16.24 using a spectrometer that generates radiation hav-

ing a frequency of 330 MHz.

16.26.Describe the effect of spin-spin coupling on the pro-

ton NMR absorptions of (a)butane, (b)cyclobutane, and (c)

isobutane (2-methylpropane). How would you tell these com-

pounds apart by their NMR spectra?

16.27.Use the NMR spectra and molecular formulas in Figure

16.26 to determine tentative identifications of the compounds.

Assume the compounds are pure. Use the NMR correlation

chart (Figure 16.23) to assist your identification.

16.28.Calculate the changes in the nuclear energy levels of

a^35 Cl nucleus (I^32 ) exposed to a magnetic field of 3.45 T.

The gNvalue for^35 Cl is 0.5479.

16.29.Calculate the Evalues of the allowed transitions for

a^35 Cl nucleus (I^32 ) exposed to a magnetic field of 3.45 T.

The gNvalue for^35 Cl is 0.5479. Express the answers in MHz.

16.30.Although boron atoms have a nonzero nuclear spin,

boron NMR is more complicated than proton NMR or^13 C

NMR. Why?

16.31.A microwave oven emits radiation having a frequency

of 2.45 GHz. What magnetic field is necessary to see NMR

transitions of^119 Sn, which has a spin of ^12 and a gNvalue of

2.0823?

16.32.Make a table of Landé gfactors for L, S, and Jhaving

values of up to 4. Comment on the effect of the various gfac-

tors on the magnitude spectra of atoms.

Exercises for Chapter 16 585

10

Chemical shift ( )

0

ppm

(a) C 3 H 6 O 2

Intensity

8642

3H

3H

Reference

peak

(TMS)

10

Chemical shift ( )

0

ppm

(b) C 4 H 9 Br

Intensity

8642

2H

6H

1H

TMS

Figure 16.26 NMR spectra.

Symbolic Math Exercises