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Cairo University
Faculty of Science
Department of Chemistry
Spectroscopic Analysis (Chem. 345)
1
Type One
Answer Sheet
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Choose only one letter (a,b,c or d) for each question
2
Choose the correct answer as a , b , c or d in the answer sheet
1. The I.H.D value of a compound having molecular formula C9H12Cl2N2O is :
a) 5
b) 4
c) 6
d) 3
2. Which of the following bonds has the lowest IR stretching frequency :
a) C—O
b) C—C
c) C—Br
d) C—Cl
3. The oxygen-containing compound which shows no IR absorption at 1780-1650 cm-1 nor at
3550-3200 cm-1 is likely to be :
a) ethyl alcohol
b) acetaldehyde
c) dimethylether
d) acetone
4. The compound which shows no symmetrical and asymmetrical stretching absorption is :
a) acetamide
b) acetic acid
c) nitroethane
d) acetic anhydride
5. The compound which shows a band at 2150 cm-1 in its IR spectrum :
a) butanol
b) butanal
c) butyne
d) butanone
6. Which order is the correct one for the C=O stretching values in the following :
I. CH3—CHO
II. CH3—CO—CH3
III. Ph—CO—CH3
a) I>II>III
b) II>I>III
c) III>II>I
d) III>I>II
7. Which one of the following statements is NOT correct :
a) intramolecular H-bonding shifts the stretching frequency of O—H to left
b) the O—H stretching band of an alcohol at infinite dilution is sharp
c) H-bonding in carboxylic acids is stronger than that in alcohols
d) H-bonding changes the IR band from sharp to broad
8. What is the proper order for the C=O absorption in the following compounds :
a) II>I>III
b) III>II>I
9. Hook’s law states that :
a) v’ = 12.4 (K/μ)1/2
c) III>I>II
b) v’ = 4.12 (μ/K)1/2
d)I>II>III
c) v’ = 1/2ЛC (K/μ)1/2
d) none
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10. The arrangement in the order of decreasing V’ of C=C values of the following compounds :
I. CH2=CH—CH=CH2
II. CH3C(CH3)=CH—CH3
III. CH2=CH—CH2—CH=CH2
a) I>III>II
b) III>II>I
c) II>III>I
d) I>II>III
11. Which compound gives bands at 3300(br.) , 2120 , 1450 , 1030 cm-1 :
a) H—C≡C—CH2OH
b) CH2=CH—CH2OH
c) H—C≡C—CHO
d) CH2=CH—CHO
12. The compound which shows two bands in the region 3500-3300 cm-1 :
a) ethyl alcohol
b) ethylamine
c) triethylamine
d) diethylamine
13. The molecular formula which shows two bands at 1850 and 1760 cm-1 is :
a) C5H10O3
b) C4H8O2
c) C4H6O3
d) C4H5Ocl
14. The compound which shows a band at 2200 cm-1 is :
a) CH2=CH—O—CH3
b) CH3—C≡CH
c) Ph--CH=CH2
d) CH3—CHO
15. Which one of the following compounds absorb at higher C=O stretching frequency than the
C=O of CH3CHClCH2COCH3 :
a) ClCH2CH2CH2COCH3
b) CH3CH2CHClCOCH3
c) CH3CH2CHBrCOCH3
d) CH3CHBrCH2COCH3
16. The index of H-deficiency of the compound having molecular formula C6H3N2O4Cl is :
a) 4
b) 6
c) 5
d) 7
17. The values of CH stretching vibrations attached to differently hybridized carbon atoms are
arranged in the order :
a) sp > sp3 > sp2
b) sp > sp2 > sp3
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2
c) sp > sp > sp
d) sp2 > sp > sp3
18. Which one of the following compounds absorbs at higher C=O stretching frequency :
a) CH3OCOCH=CH2
b) CH3OCOCH2CH3
c) CH2=CHOCOCH3
d) HCOOCH2CH2CH3
19. The compound which shows a band at 1725 cm-1 in its IR spectrum is :
a) propane
b) propanol
c) propyne
d) propanal
20. Which one of the following compounds shows two C=O stretching frequencies :
a) CH3COOH
b) CH3COCl
c) CH3COOCOCH3
d) CH3CONH2
21. The IR stretching frequency occurs at the highest value for :
a) C—H
b) C=O
c) C—Br
d) C=N
22. The IR absorption bands near 3500 cm-1 (w) and 1690 cm-1 (s) indicate the presence of :
a) an acid
b) an ester
c) an amine
d) an amide
23. Which of the following information CANNOT be obtained from an IR spectrum :
One)
The presence of C=O bond
Two)
The molecular mass
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Three)
Four)
The presence of O—H bond
The identity of a compound through comparison with other spectra
24. Which one of the following compounds would show a broad absorption band at 3400-2500 cm-1
in its IR spectrum :
a) ethanol
b) ethylamine
c) acetic acid
d) diethylamine
25. To check that a secondary alcohol is completely oxidized to a ketone , you can :
One)
check that IR has absorption bands near 3500 cm-1 and 1715 cm-1
Two)
check that IR has no absorption bands near 3500 cm-1
Three)
check that IR has no absorption bands near 1715 cm-1
Four)
check that IR has absorption band near 1715 cm-1
26. Which one of the following compounds absorb at higher C=O frequency :
a)
b)
c)
d)
27. Arrange the indicated bonds in the order of increasing stretching vibration frequency :
a) II , I , III
b) II , III , I
c) I , II , III
d) III , II , I
28. The index of H-deficiency of a compound having the molecular formula C8H7Cl2N3O3S2 is :
a) 4
b) 5
c) 6
d) 7
29. Which one of the following C—F bonds will absorb at higher wave number in IR :
a)
b)
c)
d)
30. Which one of the following compounds would show IR bands at 2150 cm-1 and 3300 cm-1 :
a) CH3CH2C ≡ CCH3
b) H2NCOCH2C ≡ N
c) CH3CH2C ≡ CH
d) CH2=CH—CH=CH2
31. The values of the CH stretching vibrations attached to differently hybridized carbon atoms
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are arranged in the order :
a) sp>sp3>sp2
b) sp3>sp2>sp
c) sp2>sp>sp3
d) none
32. The compound which shows a broad band at 3500-3300 cm-1 in its IR spectrum is :
a) propanone
b) propanol
c) propyne
d) propanal
33. Intoduction of C=C bond adjacent to a carbonyl group results in :
a) higher frequency of C=O
b) higher frequency of C=C
c) lower frequency of C=O
d) has no effect on C=O frequency
34. Decreasing the size of C=O containing cyclic compounds results in :
a) higher frequency of C=O
b) lower frequency of C=O
c) has no effect on C=O frequency
d) none
35. In nitro group , symmetric stretch is :
a) higher than asymmetric
c) equal to asymmetric
b) less than asymmetric
d) all the above are wrong
36. Intramolecular hydrogen bonding to C=O group results in :
a) decreasing the frequency of C=O
b) Increasing the frequency of C=O
c) makes the C=O band broad
d) has no effect on frequency of C=O
37. The compound which shows a band at 720 cm-1 in its IR spectrum is :
a) CH3CH2CH2CH2CH(CH3)CH3
b) CH3(CH2)2CH(CH3)CH(CH3)CH3
c) CH3(CH2)6CH2CH3
d) CH3CH(CH3)CH(CH3)CH3
38. Which of the following organic compounds shows two C—O bands at 1300-1000 cm-1 in its
IR spectrum :
a) CH3COOH
b) CH3—O—CH3
c) CH3COOCH2CH3
d) CH3CH2OH
39. The band appears at 1375 cm-1 in IR spectra can be used to distiguish between :
a) propanone and propanal
b) pentane and 2-methylbutane
c) o- and p-chloro toluene
d) 1-propanol and 2-propanol
40. The Double-beam IR spectrometer is used to detect the IR spectra of :
a) gas sample
b) solution sample
c) liquid sample
d) solid sample
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Answer key of some questions
1,16,28 )………………. I.H.D = C – H/2 – X/2 + N/2 + 1
2,21,27 ) ……………… and any arrangement question of functional groups
C≡N
O—H
C=O
C—O
C=N
N—H
C—C
C≡C
C—Cl
C=C
C—Br
C H
4000
3000
2000
1700
1600
600
10) The true resonance affects the V’ much more than hyperconjugation ( 2ry resonance )
13) The anhydride C,H,O3 ( the I.H.D must be 2 or more )
17,29,31 ) ≡ C—H (sp) band at 3300 cm-1
= C—H (sp2) band at 3100 cm-1
-- C—H (sp3) band at 2950 cm-1
( or any other C—X bond
sp>sp2>sp3 )
23) The molecular mass is known only from mass spectra
25)
complete oxidation
CH3CH(OH)CH3
( OH band must
disappear completely )
CH3COCH3
( C=O band must appear
alone at 1715 cm-1 )
4,35) symmetrical stretching < asymmetrical stretching
both appear in the functional groups : NH2 , NO2 , CO—O—CO
37) The band at 720 cm-1 appears for compounds having FOUR adjacent –CH2—groups
38) Alcohols show one C---O band in IR spectrum
Acids show one C—O band but higher in V’ than in alcohols due to resonance , where C—O
bond acquires double bond character
Esters show two C—O bands due to resonance where one C—O bond acquires double bond
character while the other is singly bonded .
CH3-CH2-OH < CH3-COOH
One C—O band
CH3-COOCH2CH3
two C—O bands
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Type Two
Answer the following questions :
1.
Arrange the following functional groups in the order of increasing stretching frequency :
a) O-H
b) C-C
c) C=O
d) N-H
e) C-O
f) C=N
g) C≡N
2.
How can you differentiate between each pair of the following compounds using IR
spectroscopy :
One)
1-butyne and 2- butyne
Two)
1,3- butadiene and 1,4- pentadiene
Three)
o- hyhroxybenzoic acid and p- hydroxybenzoic acid
3.
The following compounds show C=O stretching frequencies at 1680 , 1720 , 1735 and 1770
cm-1
Which is which ?
One)
CH3CH2CH2COOCH2CH3
Two)
CH2=CH-OCOCH3
Three)
PhCOOCH3
Four)
Methyl salicylate
4.
Explain why :
a) The stretching frequencies of carbon-hydrogen bond are arranged in the order
≡C—H > =C—H > -C—H
b) The compound with M.F C5H10O3 is not likely to be an anhydride
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5.
Deduce the structure of a compound whose M.F is C9H6N2 which gives the following bands
in
IR spectrum : 3100 , 2220 , 2150 , 2960 , 1600 , 1500 and 830 cm-1
6.
Arrange the C=O stretching frequencies of the following compounds in increasing manner .
Give reasons
7.
How would the IR spectra of the following compounds differ :
8.
Explain why :
a) O-H stretch of acids is extremely broad in the range 3400-2400 cm-1 , while O-H stretch of
alcohol is a broad in the range 3500-3200 cm-1.
b) C—H stretch occurs to the left of 3000 cm-1 , while C—C stretch occurs in the finger print
region .
Three)
While the normal C=O stretching frequency in organic compounds is approximately
1725 cm-1
the frequency of the C=O stretching bands in acid chlorides and acid amides are observed
at 1800 and 1680 cm-1 respectively.
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9.
Deduce the structure of the compound that is consistent with IR data given in each of the
following
One)
C7H8O : 3050 , 2960 , 1600 , 1250 cm-1
Two)
10.
C9H6O2 : 3400-2400 (br.) , 2120 , 1690 , 760 , 690 cm-1
Match the following stretching vibration frequencies of C=O with the proper compound :
a) 1690 , 1670 cm-1
b) 1690 cm-1
c) 1670 cm-1
11.
Predict :
One)
The structure of two isomers with M.F C8H16 , one is IR active and the other is IR
inactive
Two)
The structure of the compound C4H2O2 which shows a C=O band at 1780 cm-1
Three)
The position and shape of OH band of methyl salicylate ester after dilution with CCl4
Four)
3050 ,
The structure of the compound with M.F C7H7NO which shows IR bands at 3300 ,
1690 , 750 and 690 cm-1
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12.
Compare between each pair of the following W.R.TO the functional group indicated :
a) An amine and an amide
( C—N stretch )
b) Phenol and cyclohexanol
( C—O stretch )
c) A ketone and an amide
( C=O stretch )
d) Pure ethanol and ethanol / CS2
( O—H stretch )
e) 1ry amine and 3ry amine
( N—H stretch )
f) cis-2-hexene and trans-2-hexene
( C=C stretch )
g) An acid and an alcohol
( C—O stretch )
13.
Predict :
One)
The class of an oxygen-containing compound which shows an absorption band at
-1
1700 cm
and no absorption bands at 3300 , 2700 or 1300 cm-1 .
Two)
The class of a nitrogen-containing compound which shows no absorption bands at
3400 cm-1
and no absorption bands between 1700 and 1600 cm-1 .
14.
sp3
15.
Which would show an absorption band at larger wavenumber : A carbonyl group bonded to
hybridized carbon or a carbonyl group bonded to sp2 hybridized carbon . Explain
Arrange the following compounds in the order of decreasing V’C=O values . Explain
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Type Three
Answer the following questions :
1.
Deduce the structure of compounds A , B and C which have the following IR spectra :
C8H6
A
HgSO
4
/ H2SO4
C8H8O
H2O
B
H
2
/ Ni
C8H10O
C
Compound A
Compound B
Compound C
Compound A
Compound B
Compound C

I.H.D =
I.H.D =
I.H.D =
Important IR bands in spectrum A :
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B:
C:
2.
The elemental analysis of an organic compound give the following data : %C 31.82 , %H
2.67 ,
%N 18.55 . The mass spectrum shows molecular ion peak at m/z 75 , and M/M+2 ion peaks
with ratio 3:1 . Its IR spectrum is given below :
The molecular formula of the compound is :
The I.H.D =
The suggested structure is :
3.
The elemental analysis of an alkyl halide give the data : %C 30.5 , %H 2.55 . The mass
spectrum
shows a molecular ion peak at m/z 118 and M/M+2 ion peaks with ratio 1:1 . Its IR spectrum is
given below :
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The molecular formula is :
I.H.D =
Structure is :
4.
Deduce the structure of the following compound whose IR spectrum is given below :
C9H8O
Structure is :
5.
Which of the following compounds could give rise to each of IR spectra shown :
a) Isobutyraldehyde
b) Ethyl vinyl ether
c) 2-butanone
d) Cyclopropyl carbinol
e) Tetrahydrofuran
f) 3-buten-2-ol
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6.
The IR spectrum given is the spectrum of ONE of the following compounds .Identify it
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7.
Assign a structure to each of the spectra shown :
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