Question

What type(s) of molecular motion is (are) observed using infrared spectroscopy?

A. Stretching and bending

B. Rotation and excitation

C. Spin flipping

D. Fragmentation

4. The functional group region of an infrared spectrum is:

A. Where the cations appear

B. Greater than or equal to 1500 cm–1
C. Less than 1500 cm–1

D. Greater than or equal to 2500 cm–1

Answer 1

Infrared spectroscopy deals with the vibrations in a molecule. When the vibrating frequency of a bond becomes equal to the frequency of the given radiation then it absorbs infrared radiation and excites to higher energy levels.

1.

Molecular vibrations are mainly of 2 types i.e. stretching and bending.

During bending , change in bond angle occurs while during stretching bond length changes.

Answer -- A. Stretching and bending

2. 600 to 1500 cm-1 is known as fingerprint region while 1500 to 4000 cm-1 is called functional group region because in this region all functional group shows their characteristic absorption frequencies.

Answer -- B. Greater than or equal to 1500 cm-1