SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Try to do the exercises by yourself, then go to the answers and think why.
Problem 1. Which one of the C
5
H
8
isomers shown has its λ max
at the longest wavelength ?
Answer
Problem 2. In the solution of hexane, the absorption maximum of a compound is at
305nm, whereas in aqueous solution the absorption maximum is at 307nm. The n→π* transition or the π→π* , which leads to the absorption ?
Answer The absorption band which is made by π→π* transition .
Problem 3. Which can you indentify each of the following compounds to absorb in the IR spectrum and give the reasons?
(1)
CH
3
CH
2
CH
2
OH and
CH
3
CH
2
NHCH
3
(2)
O
(3) CH
3
C CCH
3 and
OH and CH
3
CH
2
C CH
(4) CH
3
CH
2
CH
2
OCH
3 and CH
3
CH
2
COCH
3
Answer (2) (3) (4)
Problem 4. Indicate which of the two given compounds is responsible for the IR spectrum?
(1)
(2)
O
1 / 6

SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Answer
(2)
O
Problem 5. How many signals would you expect to find in the H NMR spectrum of the following compound 1-Bromobutane?
Answer To test for chemical-shift equivalence. Replace the protons at C-1. C-2.
C-3 and C-4 of 1-bromobutane by some test group such as chlorine. Four constitutional isomers result:
This separate signals will be seen for the protons at C-1. C-2. C-3 and C-4 Bar-ring any accidental overlap. We expect to find four signals in the NMR spectrum of
1-bromobutane.
Problem 6. Which of the following nucleies does NOT have Spin angular momentum?
A.
15
N
7
B.
28
Si
14
C.
31
P
15
D.
33
S
16
Answer B
Problem 7. The shielding constant order of three different protons is σ
B
> σ
A
> σ
C .
Then what is the order of resonance frequency in the same magnetic field intensity?
Answer ν
A
< ν
B
< ν
C
Problem 8. Ficst’s acid sodium is dissolved in D
2
O. The
1
H NMR spectra shows there are two peaks with the same height, which one is its structure?
Answer Ⅱ
Problem 9. Look carefully at the
1
H NMR spectra of one compound C
8
H
10
O, what
2 / 6

is it?
SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Answer
H
2
C CH
2
OH
Problem 10. How many signals would you expect to see in the
13
C NMR spectrum of each of the following compound?
Propylbenzene
Answer The two ring carbons that are ortho to the propyl substituent are equivalent and so must have the same chemical shift. Similarly, the two ring carbons that are meta to the propyl group are equivalent to each other. The carbon atom para to the substituent is unique, as is the carbon that bears the substituent. Thus, there will be four signals for the ring carbons, designated w, x, y, and z in the structural formula.
These four signals for the ring carbons added to those for the three nonequivalent carbons of the propyl group yield a total of seven signals.
Problem 11. Calculate the value of (M+2/M) and (M+4/M) of the following three compounds.
(1)C
7
H
6
Br
(2)CH
2
Cl
2
(3C
2
H
4
BrCl(Neglected the impacts of
13
C 、 2
H)
3 / 6

SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Answer (1) 2:1 and 1:1 (2) 6:9 and 1:9 (3) 4:3 and 1:3
Problem 12. Knowing what to look for with respect to isotopic clusters can aid in interpreting mass spectra. How many peaks would you expect to see for the molecular ion in each of the following compound? At what m/z values would these peaks appear?
(Disregard the small peaks due to
13
C and
2
H)
P-Dichlorobenzene
Answer The two isotopes of chlorine are
35
Cl and
37
Cl. There will be three isotopically different forms of p-dichlorobenzene present. They have the structures shown as follows. Each one will give an M
+
peak at a different value of m/z.
Problem 13. A liquid compound C
4
H
8
O
2
(b. p 163 ℃ ) gives the Mass spectra presented in the following figure. Deduce the structure.
Answer CH
3
CH
2
CH
2
COOH
Problem 14. Found: Compound A C 47.0 %, H 2.5 %, solid, m. p 83 ℃ ;
Compound B C 49.1 %, H 4.1 %, liquid, b.p 181 ℃
Their Mass spectrums are presented in the following figure (a) and (b). Deduce the structures.
4 / 6

SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Answer
CH
3
(b)
(a) Cl NO
2
Br
Problem 15. The molecular formula is C
9
H
10
O. The
1
H NMR spectrum and the IR are shown in the following pictures. Please give the structure of the compound.
5 / 6

SPECTRUM ELUCIDATION
HEBEI UNIVERSITY OF SCIENCE AND TECHNOLOGY
Answer
CH
2
COCH
3
Problem 16. Deduce the structure
C
10
H
10
O
2
NMR Solvent: CDCl
3
1
H NMR Spectrum
13
C NMR Spectrum
Answer
6 / 6