24.4 Nuclear Magnetic Resonance Spectroscopy 1023
PROBLEMS
Section 24.4: Nuclear Magnetic Resonance Spectroscopy
24.21Find the magnetic field in tesla and in gauss necessary to
carry out NMR experiments at 200.00 MHz with the^7 Li
nucleus, which has a nucleargNfactor equal to 2.171 and
a nuclear spin numberI 3 /2.
24.22a.Describe qualitatively the high-resolution proton
NMR spectrum of carefully purified propionic acid
(propanoic acid).
b.Describe the spectrum of propionic acid with a small
amount of water present.c.Describe the spectrum of a dilute anhydrous solution
of propionic acid in deuterated chloroform.24.23a.Describe qualitatively the high-resolution proton
NMR spectrum of carefully purified acetic acid
(ethanoic acid).
b.Describe the spectrum of acetic acid with a small
amount of water present.c.Describe the spectrum of a dilute anhydrous solution
of acetic acid in deuterated chloroform.24.24Describe qualitatively the high-resolution proton NMR
spectrum of
a.Methyl ethyl ketone (butanone)
b.Formaldehyde (methanal)
c.Formic acid (methanoic acid)
Look up the spectra and compare your predictions with
the correct spectra.
24.25Predict qualitatively the high-resolution proton NMR
spectrum of CH 3 F.
24.26Sketch the proton NMR spectrum you would expect from
each of the following. Indicate approximate chemical
shifts.
a.Butanone (methyl ethyl ketone)
b.2-Propanol (isopropyl alcohol)
c.Ethane
d.Ethanal (acetaldehyde)
24.27a.A compound of empirical formula C 2 H 3 Cl 3 has a
high-resolution proton NMR spectrum with a single
line. What is the structural formula of the compound?
b.Predict the high-resolution proton NMR spectra of the
other isomers of this compound.
24.28Predict the proton NMR spectrum of each of the
following substances. Include approximate values of the
chemical shift relative to TMS. Give relative areas for the
lines.
a.Acetone
b.Methyl acetate
c.Propane
24.29The coupling constant for two protons in a given
molecule isJ 3 .5 Hz. In a proton NMR spectrum taken
in a 200 MHz instrument, what is the spin–spin splitting
between the lines when the spectrum is displayed with the
axis in ppm?
24.30Describe qualitatively the high-resolution proton NMR
spectrum of
a.tert-Butyl alcohol (1,1-dimethylethanol)
b.sec-Butyl alcohol (1-methylpropanol)
c.Primary butyl alcohol (butanol)
Look up the spectra and compare your predictions with
the correct spectra.
24.31a.Tell how you would distinguish diethyl ether,
n-butanol, andtert-butanol from each other using
proton NMR.
b.Tell you how would distinguish acetone from propanal
using proton NMR.
24.32Tell how you would distinguish the following pairs of
substances using proton NMR:
a.CH 3 F and CH 3 Cl
b.Methyl formate and acetic acid
24.33a.Predict the ESR spectrum of the cyclopropenyl
radical.
b.Predict the proton NMR spectrum of the
cyclopropenyl radical.