Vibrational Spectrum of Acetone
Molecules vibrate in response to their
absorbing infrared light. Absorption occurs only at specific wavelengths,
which gives rise to the use of vibrational (infrared/Raman) spectroscopy
as a tool for identifying chemical structures. The energy or frequency
of a particular vibration is proportional to the square root of a quantity
called a "force constant" divided by a quantity called the "reduced
mass".
The force constant depends on
the "flatness" or "steepness" of the energy surface
and reflects the difficulty of moving the atoms involved in the vibration
from their equilibrium positions. The steeper the energy surface, the
larger will be the force constant and the larger the frequency. The reduced
mass reflects the total (weighted) mass of the atoms involved in the vibration.
The smaller the mass, the larger will be the frequency.
Acetone may be used to explore the relationship between frequency and
force constant, and further to examine why certain frequencies are of
particular value in the use of vibrational spectroscopy as an analytical
tool.
Build acetone. Click on .
Start with sp^{2} carbon (),
add sp^{2} oxygen ()
to make the carbonyl group and then add two sp^{3} carbons ().
Click on
and then on .
