Introduction to Soil Chemistry

% Transmittance
% Transmittance
120
100
80
60
40
20
infrared spectroscopy 165
0
4000 3500 3000 2500 2000 1500 1000
Wavenumber cm –1
120
100
80
60
40
20
Hexanoic acid
C
O
OH
Octene Octyne 1-Hexanol
H
C OH
H
C C
0
4000 3500 3000 2500 2000 1500 1000
Wavenumber cm –1
Figure 8.11. Infrared spectra showing common absorption. Both the OH of acids and alcohols
are hydrogen-bonded, lending to broadening of the absorption. Note that the OH absorption of
hexanol is unusually sharp for a hydrogen-bonded alcohol.
8.11.1. Infrared Sample Preparation
All compounds have absorptions in the midinfrared region of the spectrum.
Most common solvents contain groups that absorb in this region of the spectrum,
which are important for identification of unknowns and thus are not
used. Carbon tetrachloride, carbon disulfide, and mineral oil (often called
nujol) are exceptions, in spite of the fact that all three have significant infrared
absorbences. Mineral oil, for example, has strong absorbences due to —CH 3,
—CH2— in its molecules. This obscures regions that may be of analytical
O
C
C C