Review of linear harmonic oscillator, the vibrating diatomic molecule, the simple harmonic oscillator, the anharmonic oscillator, the diatomic vibrating rotator, the vibration-rotation spectrum ofcarbon monoxide, breakdown of the Born-Oppenheimur approximation, the vibration of polyatomic molecules, overtones and combination frequencies, the influence of rotation on the spectra of polyatomic molecules, the influence of nuclear spin, symmetric top molecules, analysis by Infra-red technique - Group frequencies, outline of technique and instrumentation.
Multiple choice Questions:
1.
The spectra caused in the infrared region by the transition in vibrational
levels in different modes of vibrations are called
(a) rotational
spectra
(b) electronic
spectra
(c) vibrational
spectra
(d) none
of these
2.
The IR spectra of a compound helps in
(a) proving
the identity of compounds
(b) showing
the presence of certain functional groups in the molecule
(c) neither
of the above
(d) both
of the above
3.
The Raman and IR spectra can tell us whether
(a) a
molecule is linear or non-linear
(b) a
molecule is symmetrical or asymmetrical
(c) neither
of the above
(d) both
of the above
4.
What does IR spectroscopy allow us to determine?
(a) the
molecular formula of a compound
(b) the
kinds of bonds in a compound
(c) the
molecular weight of a compound
(d) the
number of carbons in a compound
5.
Which of the following will show an absorption band at the greatest wavenumber?
(a) C=C
(b) C≡C
(c) C=O
(d) C–N
6.
Which of the following bonds will show an absorption band at the greatest
wavenumber?
(a) C=O
(b) C=C
(c) O–H
(d) C–H
7.
Hooke's law relates the restoring force, f to the displacement q
as
(a) f=
-Kq
(b) f
= Kq
(c) f=
Kq2
(d) f=-
Kq2
8.
The lowest energy of a quantum mechanical harmonic oscillator is 1/2 hv. It
is referred to as
(a) Ground
state energy
(b) Zero-point
energy
(c) Vibrational
energy
(d) All
9.
The intensity of an absorption band is always proportional to the
(a) Atomic
population
(b) Molecular
population of the initial state
(c) Molecular
population of the final state
(d) Temperature
10.
The vibrational stretching frequency of diatomic molecule depends on
(a) Force
constant
(b) Masses
of two atoms
(c) Both
(a) and (b)
(d) None
11.
Force constant is expressed in
(a) Dynes
cm-1
(b) m.dyne
Ao-1
(c) Nm-1
(d) All
12.
The amplitude of the vibration, q for NO, CO, HCI is 0.048 Å, 0.05 Å,
0.10 Å. Thus q is
(a) Larger
when the force constant is smaller
(b) Smaller
when the force constant is smaller
(c) Larger
when the force constant is larger
(d) None
13.
Since the nuclei in a polyatomic molecule do not always vibrate in a simple
harmonic manner, there arises
(a) Harmonicity
(b) Anharmonicity
in molecular vibrations
(c) Fundamental
frequencies
(d) All
14.The
frequency of vibration of H, is 4159 cmand dissociation energy is 4.5 eV.
Assuming that it vibrates as a SHO, its vibrational quantum number
corresponding to dissociation energy, D is
(a) 8
(b) 10
(c) 7
(d) 6
15.
The vibrations, without a centre of symmetry are, active in
(a) Infrared
active but inactive in Raman
(b) Raman
but inactive in IR
(c) Raman
and IR
(d) None
16.
The frequency of vibration of a bond is a function of
(a) Force
constant of the bond
(b) Masses
of the atoms involved in bonding
(c) Both
(a) and (b)
(d) Bond
order
17.
In poly atomic molecules, silent vibrations which involve no change of dipole
moment or polarizability are
(a) IR
active but Raman inactive
(b) IR
inactive but Raman active
(c) Neither
IR active nor Raman active
(d) Both
IR and Raman active
18.
Total number of vibrations in allyl bromide, CH2=CHCH2Br
are
(a) 18
(b) 21
(c) 14
(d) 16
(Hint. 3n - 6 gives 3x9-6 = 21 vibrations).
19.
The predominant advantages provided by interferometer compared to
dispersive instruments are
(a) Jaquinot
advantage
(b) Fellgett
advantage
(c) Connes
advantage
(d) All
20.
The vibrational degrees of freedom for (i) O2 (ii) N2O
(iii) CH2O (iv) C6H6 (v) CHCl3 are respectively
(a) 3,
1, 6, 6, 30
(b) 1,
3, 9, 30, 6
(c) 1,
3, 6, 30, 6
(d) 3,
6, 9, 6, 15 (Hint Vibrational degrees of freedom for linear molecules = 3n -
5 and for non-linear = 3n
– 6)
21. The C–H stretching frequency for an alkane
is 2900 cm-1. The value for C-D frequency is
(a) 2900
cm-1
(b) 2060
cm-1
(c) 2860
cm-1
(d) 2250
cm-1
22.
The order of decreasing vibrational frequency for C—CI, C-Br, C-C, C-O and C-H
is
(a) C-H,
C-C, C-O, C—CI, C-Br
(b) C-CI,
C-Br, C-C.C-H, C-O
(c) C-O,C-H.
C-Br, C-CI, C—C
(d) C-Br,
C-Cl, C-C.C—O, C-H
23.
Ethanol and glycol in CCl4 exhibit broad O-H str. near 3350cm-1
in IR spectra. On dilution with CCl4, the spectrum of glycol
does not change but that of ethanol exhibits a sharp band at 3600 cm-1
in addition to band at 3350 cm-1 because
(a) Intermolecular
H-bonding is concentration dependent
(b) Intramolecular
H-bonding is not affected on dilution
(c) Both
(a) and (b)
(d) None
24.
The exceptionally low carbonyl stretching frequency (1650 cm-1)
in 2,4,6-cycloheptatrienone is due to
(a) Conjugation
effect
(b) Steric
effect
(c) Field
effect
(d) Electronic
effect
25.
In the IR spectrum of aroyl chloride, a weak band near 1750 cm-1
results from
(a) Inductive
effect
(b) Fermi
resonance between C=O band and first overtone
(c) Conjugation
effect
(d) All
26.
Compound C5H10 shows no absorption at 1380 cm-1.
It is
(a) Pentene
(b) Cyclopentane
(c) Pentyne
(d) All
27.
Ketones absorb in IR at a very high frequency (2150 cm-1)
because
(a) The
inner C is sp-hybridised
(b) The
more s character in a bond, the stronger it is
(c) Inner
C is sp2 hybridised
(d) Both
(a) and (b)
