SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Comprehensive Exercises 1
Try to do the exercises by yourself, then go to the answers and think why.
Problem 1. Which spectrum provides the information of structure?
(1) Relative Molecular mass
(2) conjugation
(3) functions groups
(4) proton chemical surrounding
Answer
(1)MS
(3)IR
(2)UV
(4)1H NMR
Problem 2. In the solution of methanol, the absorption maximum is at 284nm.
Which is the structure of the compound, A or B?
CH3
H3C
O
O
O
H3C
OH
OH
A
Answer
O
H3C
B
A
Problem 3. For each of the following pairs of compounds, indentify which has the
longerλmax?
CH3
CH2
and
(1)
O
O
NH2
(2)
(3)
and
and
CH3CH CH2
CH3CH CHOCH3
Answer
(1)
O
Problem 4.
CH2
(2)
NH2
(3) CH3CH CHOCH3
An IR spectrum of compound has been given in the following figure?
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HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
IR spectrum
(1) The compound is an aromatic type of compound or aliphatic compound?
(2) Which groups may present in the 1000～4000cm-1rang, and which not?
Answer
(1) Aromatic type of compound
(2)It may include –NH2, because primary amines show two bands in 3500cm-1
OH ,
C O
,
and unsymmentrical
C N
are not presented
C C
Problem 5. Describe the appearance of the 1HNMR spectrum of each of the
following compound. How many signals would you expect to find, and into how
many peaks will each signal be split?
1,2-Dibromobutane
Answer
All protons of 1, 2-dichloroethane (ClCH2CH2Cl) are chemically
equivalent and have the same chemical shift. Protons that have the same chemical
shift do not split each other’s signal. And so the NMR spectrum of 1, 2-dichloroethane
consists of a single sharp peak.
Problem 6. At a field strength of 1.9406 T, calculate the resonance frequency of 1H、
13
C、9F、13P.
Answer
82.6MHz、20.8MHz、77.7MHz、33.4MHz.
Problem 7. In each of the following pairs of compounds, which of the underlined
protons has the greatest chemical shift?
(1)
a
(2)
a
Answer
CH3
CH3CH3
(1)
b
c
CH2
b
CH3CH2Cl
(2)
c
c
CHO
CH3CH2I
b
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SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Problem 8. A compound C8H18O2, In the 1H NMR spectrum, there is a singlet at
δ1.0 ppm. Deduce its structure.
Answer
(CH3)3CO(CH3)3
Problem 9. Propose structures for compounds with the following formulas that show
singlet in their 1H NMR spectrum?
(1)
C5H12
Answer
(2)
C3H6Br2
(3)
C2H6O
(4)
C3H6O
(5)
C4H6
(6)
C8H18
(1) (CH3)4C (2) CH3CBr2CH3
(3) CH3OCH3
(4) CH3COCH3
(5) CH3CCCH3
(6) (CH3)3C-C(CH3)3
Problem 10. A compound with formula C9H13N gives the 1H NMR spectra, please
propose the structure.
1
H NMR spectra
Answer
H2 CH3
C N
CH3
Problem 11. Calculate the value of (M+2/M) of the following three compounds.
(1)C2H5Br
(2)C6H5Cl
(3)C2H4SO2 (Neglected the impacts of 13C、2H)
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SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Answer
(1) 1:1
(2) 1:3
(3) 1:23
Problem 12. One beam of ions with different m/z values go through one single
focusing Mass Spectrometer with fixed value of r and V, if magnetic field intensity is
varying from low to high , then the first ion coming out and detected is the one with
bigger or smaller m/z value ?
Answer
The one with the smallest m/z value.
Problem 13. Look carefully at the following figure, how many fragment ion peaks are
there, and which one has the highest abundance?
C2H5
CH3
C C3H7
CH3
Answer
H3C C CH2CH3
CH3
m/z =71,
Problem 14. One compound C8H8O gives the Mass spectra presented in the following
figure. Deduce the structure and the cleavage processes of main fragment ions.
Answer
O
C CH3
Problem 15. Compound C7H8O, has important bands in its UV absorption shows
typical of the absorption a benzene ring. Its IR at 3400cm-1 (s) , Its NMR has bands at
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SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
δ4.3、δ5.1、δ7.3(s), the true ratios are 2:1:5. Assign a structure to the compound
that is compatible with spectral data given above.
Answer
CH2OH
(1) The formula is CH7O8, and there is therefore four double-bands equivalent,
suggest the formation of the benzene ring.
(2) The UV spectrum has λmax 240-290nm , the absorption is middle , and
typical of the benzene ring group, the presence of an benzene ring group is
immediately apparent in the UV .
(3) The IR spectrum with its very strong band at 1600cm-1, is shown by C=C
conjugated aryl group.
(4) From low-field to high-field, the NMR spectrum has five aromatic protons,
one hydroxyl protons , two methane protons .
Problem 16. Deduce the structure
Compound C7H8O2
NMR Solvent: CDCl3
IR Solvent: neat
IR Spectrum
1
H NMR Spectrum
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HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
13
C NMR Spectrum
Answer
3-methoxyphenol
OH
OCH3
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