Organic Chemistry Multiple Choice Questions and Answers – Infrared Spectroscopy – 2

Questions
1 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

Answer: Fermi resonance between C = O band and first overtone
2 Which compound having molecular formula C5H10 shows absorption at 1380 cm-1?
A 2-Methyl-1-butene
B Cyclopentane
C Pentyne
D Methylcyclobutane

Answer: Cyclopentane
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3 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

Answer: Inner C is sp2 hybridized
4 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

Answer: Increases carbonyl stretching frequency
5 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

Answer: Phenyl acetylene
6 What is the relation between wave number of IR absorption and the reduced mass?
A Wave number is directly proportional to reduced mass
B Wave number is inversely proportional to reduced mass
C Wave number is independent of the reduced mass
D Wave number is directly proportional to square of reduced mass

Answer: Wave number is inversely proportional to reduced mass
7 What is the number of vibrational degrees of freedom in C6H5CH3?
A 39
B 15
C 18
D 40

Answer: 39
8 Which of the following molecules will not show infrared spectrum?
A H2
B HCI
C CH4
D H20

Answer: H2
9 The phosphorescence spectrum of the excited species is due to which transition?
A Singlet to triplet transitions
B Triplet to singlet transitions
C Vibration modes
D Electron spin transitions

Answer: Triplet to singlet transitions
10 Why Monomeric saturated aliphatic carboxylic acids show carbonyl stretching frequency near 1760 cm-1, while saturated aliphatic ketones near 1720 cm-1?
A Mesomeric (M) effect is dominant in acids over the inductive (I) effect
B I effect is dominant in carboxylic acids over the mesomeric effect
C I effect on ketones is dominant over the M effect
D M effect in ketones is dominant

Answer: I effect is dominant in carboxylic acids over the mesomeric effect

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