M. Sc. Second year Postgraduate degree course
Third Semester
CHE - 313 Structural Elucidation by Spectral methods
UNIT-I Nuclear Magnetic Resonance Spectroscopy (H1 NMR)
Syllabus:-Elementary ideas (Recapitulation);Spin - spin
couplings, Different types of couplings, factors affecting on coupling
constants, Karplus equation, Spin systems (AB, AX, ABX, AMX), Rate processes,
spin decoupling, shift reagents, Nuclear Over hauser effect (NOE). INEPT & INADEQUATE.
Multiple Choice questions
1. NMR spectroscopy is
useful for determining the type and number of _______ atoms in organic molecules.
(a) hydrogen
(b) carbon
(c) halogen
(d) hetero atoms
Answer. (a)
2. What is the
multiplicity of the methylene hydrogens of a carbon that is attached to a
methyl group and to a methyl group and to a methoxy group?
(a) doublet
(b) singlet
(c) quartet
(d) triplet
Answer. (c)
3. Each of the following
compounds has a singlet in its 1H NMR spectrum. Which compound would
have its singlet at the highest frequency?
(a)
1-bromo-2,2-dimethylpropane
(b) ethyl methyl ether
(c) ethyl-tert-butyl
ether
(d) 1,2-dibromoethane
Answer. (b)
4. Which of the
following compounds would have the signal for its methylene hydrogens farthest
downfield?
(a) ethyl chloride
(b) ethyl iodide
(c) ethyl bromide
(d) ethyl fluoride
Answer. (d)
5. How many signals
would you expect to see in the 1H NMR spectrum of chlorocyclobutane?
(a) 1
(b) 3
(c) 4
(d) 5
Answer. (d)
6. What is the
multiplicity of the OH group of an alcohol in a solution that contains a trace
amount of acid?
(a) doublet
(b) quintet
(c) quartet
(d) singlet
Answer. (d)
7. How many signals
would you expect to see in the 1H NMR spectrum of butane?
(a) 1
(b) 2
(c) 3
(d) 4
Answer. (b)
8. Which of the
following will occur farthest downfield?
(a) the hydrogens of
benzene
(b) the hydrogens of
ethyne
(c) the hydrogens of
dimethyl ether
(d) the hydrogens of H COH
Answer. (d)
9. How many signals will
vinyl chloride have in 1H NMR spectrum?
(a) 1
(b) 2
(c) 3
(d) 4
Answer. (c)
10. How many signals
does 2,2,4-trimethylpentane have in its 1H NMR spectrum?
(a) 2
(b) 3
(c) 4
(d) 5
Answer. (c)
11. How many signals
would you expect to see in the 1H NMR spectrum of 2-methylpropene?
(a) 2
(b) 3
(c) 4
(d) 5
Answer. (a)
12. Which of the
following compounds is frequently used as an internal reference in 1H
NMR spectroscopy?
(a) TNS
(b) DMF
(c) TMS
(d) DMSO
Answer. (c)
13. Which of the
following describes the 1H NMR spectrum of 1,2-dichloroethane?
(a) one doublet
(b) two triplets
(c) two doublets
(d) one singlet
Answer. (d)
14. What is the
multiplicity of the CH2, hydrogens in CH3OCH2CH2OCH3?
(a) a singlet
(b) a triplet
(c) a quartet
(d) a doublet
Answer. (a)
15. What would be the
splitting of the protons on the CH2 groups of butane?
(a) doublet
(b) sextet
(c) triplet
(d) singlet
Answer. (c)
16. Only one signal is
present in the PMR spectra of
(a) C₂H4, C3H6
(b) C₂H6, C5H12
(c) C8H18,C2H6
(d) All
Answer. (d)
17. A proton Hb is
coupled to four equivalent protons Ha.The
multiplicity and relative intensity of lines in the signal Hb is
(a) Doublet, 1: 4:9.
(b) Triplet 1: 4: 6
(c) Quintet, 1: 4: 6: 4:
1
(d) Quartet 1: 4: 6: 4:4.
Answer. (c)
18.The compounds showing
only a single peak in its PMR spectrum are: Acetone (I), Ether (II), Methyl
acetate (III), Dibromoethane (IV), Chlorobromoethane (V).
(a) I, II, IV
(b) II, III, V
(c) I, III, V
(d) III, IV, V
Answer. (a)
19. The aldehydic proton
appears much downfield in the PMR because the aldehydic proton is
(a) Strongly shielded
(b) It lies in the
deshielding zone of the carbonyl group
(c) It occurs at 10 8
ppm
(d) All
Answer. (d)
20. The actual value of nuclear spin depends on
(a) Mass number
(b) Atomic number
(c) Both a and b
(d) Shielding effect
Answer. (c)
21. H¹, C13, F19, P31 have nuclear spin
equal to
(a) 1/2
(b) 1
(c) 0
(d) 3/2
Answer. (a)
22.When the effective magnetic field
experienced by the nucleus is less than that of the applied field [Heff <Ho]the
nucleus is said to be
(a) Deshielded
(b) Shielded
(c) Relaxed
(d) None
Answer. (b)
23. In p-xylene, the ratio
of methyl protons to ring protons is 6: 4 while for methylene, it
(a) 3: 2
(b) 9: 3
(c) 6: 3
(d)6:4
Answer. (b)
24. Four different type
of protons are present in allyl bromide the correct statement is/are
(a) Two enantiomeric
identical allylic protons
(b) Two diastereotopic
different protons
(c) Remaining proton
(d) All are correct
Answer. (d)
25.The 1H NMR spectrum
of 1,4-dimethoxybenzene will have
(a) Ten singlets
(b) Two singlets
(c) Two doublets and one
singlets
(d) Two doublets and two
singlets
Answer. (b)
26. More the shielding
effect
(a) Lower the chemical shift
(b) No change in chemical shift
(c) Higher the chemical shift
(d) More the peak splitting
Answer. (a)
27. Which of the
following statement is FALSE
(a) Chemical shift of
aromatic compounds is very low than alkenes
(b) Dioxane gives one
NMR peak
(c) PMR is more
sensitive than CMR
(d) Acids will have more
chemical shift than alcohols
Answer. (a)
28.Nuclei with odd
number of protons and odd number of neutrons will have spin quantum number as
(a) 1/2
(b) 3/2
(c) 0
(d) 1
Answer. (d)
29. The possible spin
states of a nucleus with spin quantum number 1/2 are
(a) 0
(b) 1
(c) 2
(d) 4
Answer. (c)
30. How many number of
peaks are possible in 1H NMR spectra of Ethyl chloriode
(a) 1
(b) 2
(c) 3
(d) 4
Answer. (c)
31. Enantiotropic
protons are
(a) Chemically
equivalent
(b) Magnetically
equivalent
(c) Both A and B
(d) Does not give NMR
signal
Answer. (c)
32. The approximate
value of methyl proton in NMR is
(a) 1.3
(b) 1.5
(c) 0.9
(d) 2.5
Answer. (c)
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