INFRARED SPECTROSCOPY Flashcards
What is the relation between restoring force, f to the displacement q in Hooke’s law?
a) f = -kq
b) f = kq
c) f = kq2
d) f = -kq2
a) f = -kq
The intensity of an absorption band is always proportional to which of the following factor?
a) Atomic population
b) Molecular population of the initial state
c) Molecular population of the final state
d) Temperature
b) Molecular population of the initial state
On which factors the vibrational stretching frequency of diatomic molecule depend?
a) Force constant
b) Atomic population
c) Temperature
d) Magnetic field
a) Force constant
In which unit Force constant is not expressed?
a) Dynes cm-1
b) dyne Å-1
c) Nm-1
d) kp
d) kp
For HCI = 1.63 x 10-27 kg, the observed frequency = 2890 or v = 8.67 x 1013 Hz. What is the force constant K?
a) 4.83 m dyn Å-1
b) 8.43 dynes cm-1
c) 483 μm-1
d) 4.83 dyn Å-1
a) 4.83 m dyn Å-1
Since the nuclei in a polyatomic molecule do not always vibrate in a simple harmonic manner, there arises which of the following situation?
a) Harmonicity
b) Anharmonicity in molecular vibrations
c) Fundamental frequencies
d) Infrared
a) Harmonicity
The vibrations, without a center of symmetry are active in which of the following region?
a) Infrared but inactive in Raman
b) Raman but inactive in IR
c) Raman and IR
d) Inactive in both Raman and IR
c) Raman and IR
The frequency of vibration of a bond is a function of which factor?
a) Force constant of the bond
b) Masses of the atoms involved in bonding
c) Force constant of the bond and Masses of the atoms
d) Bond order
c) Force constant of the bond and Masses of the atoms
What is the order of decreasing vibrational frequency for C — Cl, C — Br, C — C, C — O and C — H?
a) C-H, C-C, C-O, C- Cl, C-Br
b) C- Cl, C-Br, C-C, C -H, C-O
c) C-O, C-H, C-Br, C- Cl, C-C
d) C-Br, C- Cl, C-C, C-O, C-H
a) C-H, C-C, C-O, C- Cl, C-Br
What is the correct increasing order of stretching frequencies for C ≡ C, C = C and C — C?
a) C — C > C = C > C ≡ C
b) C ≡ C > C = C > C — C
c) C — C > C = C < C ≡ C
d) C ≡ C < C — C > C = C
b) C ≡ C > C = C > C — C
Why in the IR spectrum of Benzoyl chloride, a weak band near 1750 cm-1 is formed?
a) Inductive effect
b) Fermi resonance between C = O band and first overtone
c) Conjugation effect
d) Hyperconjugation effect
b) Fermi resonance between C = O band and first overtone
Which compound having molecular formula C5H10 shows absorption at 1380 cm-1?
a) 2-Methyl-1-butene
b) Cyclopentane
c) Pentyne
d) Methylcyclobutane
b) Cyclopentane
Why ketenes absorb in IR at a very high frequency (2150 cm-1)?
a) The inner C is sp hybridized
b) The more s character in a bond, the stronger it is
c) Inner C is sp2 hybridized
d) Inner C is sp3 hybridized
c) Inner C is sp2 hybridized
What is the effect of ring strain in lactone (cyclic ester) or a lactam (cyclic amide)?
a) Increases carbonyl stretching frequency
b) Decreases carbonyl stretching frequency
c) Increases C = C frequency
d) Decreases C = C frequency
a) Increases carbonyl stretching frequency
A compound C8 H6 decolorizes Br2 in CCl4 and gives a white precipitate with Tollen’s reagent. It has sharp band at 3300 cm-l and weak bands at 3085, 2110 cm-l. What is this compound?
a) Phenyl acetylene
b) Phenyl propylene
c) Phenyl ethylene
d) Octene
a) Phenyl acetylene
