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MCQ on IR spectroscopy: Page-1

The number of vibrational modes for the following compound is
acetaldehyde

(A) 23

(B) 24

(C) 15

(D) 9

The number of vibrational modes for non-linear molecule is 3N-6 and for linear molecule is 3N-5 where N is the total number of atoms in the molecule. Since acetaldehyde is a non-linear molecule and it has totally 7 atoms, the number of vibrational modes will be=3(7)-6=15.

2. mid-IR region mainly consists of

(A) 4000 – 100 cm -1

(B) 14000 – 4000 cm -1

(C) 4000 – 400 cm-1

(D) 400 – 100 cm -1

3. Over tones are mainly observed in

(A) near IR

(B) mid IR

(C) far IR

(D) Not in IR region

4. Read the following data. The wavelength corresponding to the peak at 1720 cm-1 is

(A) 5.81 μm

(B) 6.17 μm

(C) 5.81 nm

(D) 6.17 nm

5. The frequency of the above radiation is

(A) 15.45 x 1014 Hz

(B) 16.51 x 1012 Hz

(C) 17.47 x 1014 Hz

(D) 51.63 x 1012 Hz