Spectroscopy Review Problems

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SPECTROSCOPY PROBLEMS
Dr. Sheppard
CHEM 2412
Fall 2014
McMurry (8th ed.) sections 12.1-3, 12.5-8, 13.1-5, 13.7-11,
13.13
1. Which of the following statements best
describes the base peak in a mass
spectrum?
A. The peak from the most stable radical.
B. The peak from the species that has the isotope with the
highest atomic number.
C. The peak of highest intensity.
D. The peak from the molecule minus an electron.
2. This compound contains C, H, and one
other atom. Identify the other atom from
the mass spectrum and explain your
reasoning.
3. Consider the mass spectrum of 2methylbutane.
(a) What peak represents M+?
(b) What peak represents the base peak?
4. True or false, both mass spectrometry
and infrared spectroscopy involve the
interaction of molecules with
electromagnetic energy?
5. The amount of energy in infrared light
corresponds to:
A. the amount of energy needed to promote one electron
from a bonding to an antibonding molecular orbital
B. the amount of energy needed to "flip" the spin of a 13C
or 1H nucleus
C. the amount of energy needed to strip a molecule of one
electron to generate a cation radical
D. the amount of energy needed to increase certain
molecular motions, such as bond vibrations, in organic
molecules
6. Examining the infrared spectrum of a
compound allows us to:
A. determine the types of functional groups present in the
compound
B. determine the carbon-hydrogen framework of the
compound
C. determine the molecular weight of the compound
D. determine the nature of the conjugated pi electron
system in the compound
7. Match each of the following groups of
bond-types to the region of the infrared
spectrum in which their absorptions occur.
Place the letter of the region in the blank
to the left of the bond-type.
_____ C-C, C-O, C-N, and C-X single-bond vibrations.
_____ C=O, C=N, and C=C bond absorptions.
_____ N-H, C-H, and O-H stretching and bending motions.
_____ triple bond stretching vibrations.
A. 4000 to 2500 cm-1
B. 2500 to 2000 cm-1
C. 2000 to 1500 cm-1
D. below 1500 cm-1
8. When 1-bromopropane reacts with
ethoxide ion, two products are formed.
Write the structures of both products, and
tell how they could be distinguished using
IR spectroscopy.
9. Assume you are carrying out the
conversion of 1-bromobutane to 1-butanol.
How could you use IR spectroscopy to
determine when the reaction is complete?
10. Match a structure from the list below
to the following IR spectra.
11. Match a structure from the list below to
the following IR spectra.
12. Match a structure from the list below
to the following IR spectra.
13. Name the type of spectroscopy shown
in each spectrum.
A
C
B
D
14. Match a term to each description below.
When looking at an NMR chart the right-hand part of the chart is the _____.
The exact place on the chart at which a nucleus absorbs is called its _____.
The calibration standard for 1H and 13C NMR is _____.
The NMR charts are calibrated using an arbitrary scale that is divided into
_____ units.
A.
B.
C.
D.
E.
F.
G.
TMS
high-field or upfield side
MHz
delta (d)
low-field or downfield side
chemical shift
specific absorption
15. For each of the compounds below tell
how many signals you would expect the
molecule to have in its normal, H-decoupled
13C NMR spectra.
16. For each compound below tell how
many types of nonequivalent protons
there are.
17. Predict the splitting patterns you would
expect for each proton in the molecules
below.
18. What is the splitting pattern for the
hydrogens in 3-methyl-2-butanone
labeled a?
A. septet
B. quartet
C. doublet
D. singlet
19. What is the splitting pattern for the
hydrogens in 3-methyl-2-butanone
labeled b?
A. septet
B. quartet
C. doublet
D. singlet
20. Treatment of tert-butyl alcohol with
hydrogen chloride yields a mixture of tertbutyl chloride (SN1 product) and 2methylpropene (E1 product). After
chromatographic separation, how would
you use 1H-NMR to help you decide which
was which?
21. Propose a structure that fits the
following 1H-NMR data.
• C8H9Br
• 3H doublet at d2.0
• 1H quartet at d5.0
• 5H multiplet at d7.3
22. Propose a structure for this compound.
• C4H8O
23. Which structure of molecular formula
C4H8Cl2 fits both the 1H-NMR and 13C-NMR
spectra shown below?
A
B
C
D
24. Calculate the Index of Hydrogen
Deficiency (degree of unsaturation) for a
molecule with the molecular formula
C5H12O.

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