Vibrational frequency (cm-1)
a. 2100<BR>2100
b. 1905<BR>1905
c. 1300<BR>1300
d. 2250<BR>2250
Answers
Answer: The light our eyes see is but a small part of a broad spectrum of electromagnetic radiation.
On the immediate high energy side of the visible spectrum lies the ultraviolet, and on the
low energy side is the infrared. The portion of the infrared region most useful for analysis
of organic compounds is not immediately adjacent to the visible spectrum, but is that
having a wavelength range from 2,500 to 16,000 nm, with a corresponding frequency range
from 1.9*1013 to 1.2*1014 Hz.
Photon energies associated with this part of the infrared (from 1 to 15 kcal/mole) are not
large enough to excite electrons, but may induce vibrational excitation of covalently
bonded atoms and groups. The covalent bonds in molecules are not rigid sticks or rods,
such as found in molecular model kits, but are more like stiff springs that can be stretched
and bent.. We must now recognize that, in addition to the facile rotation of groups about
single bonds, molecules experience a wide variety of vibrational motions, characteristic of
their component atoms. Consequently, virtually all organic compounds will absorb infrared
radiation that corresponds in energy to these vibrations. Infrared spectrometers, similar in
principle to the UV-Visible spectrometer, permit chemists to obtain absorption spectra of
compounds that are a unique reflection of their molecular structure. An example of such a
spectrum is that of the flavoring agent vanillin, shown below.
Explanation: