Figure 9.23
Infrared spectrum of n-propyl acetate.3000 cm–^1 ), skeletal and overtone bands between 1400 and 2000 cm–^1 and a C—H out-of-plane bending
vibrations at 835 cm–^1 indicating p-substitution). Asymmetric and symmetric N—O stretching bands are
very prominent at 1475 and 1310 cm–^1 , whilst evidence for an amine group is given by the doublet N–H
stretching band near 3400 cm–^1 and the in-plane N—H bending band near 1600 cm–^1. A strong C—N
stretching vibration overlaps the symmetric N O band near 1300 cm–^1.
Some further examples of infrared spectra are given in the section on the combined use of spectral data.
Figure 9.24
Infrared spectrum of p-nitroaniline.Quantitative Analysis
Absorption in the infrared region of the spectrum can be expected to obey the Beer-Lambert law (p.
357) for bands which are well resolved and in the absence of chemical effects such as hydrogen
bonding. It is important that the slit width of the instrument is kept constant for a series of
measurements as band intensities are highly sensitive to changes. This is because slit widths used in
infrared spectrometry are of the same order of magnitude as bandwidths. A commonly used method for
establishing the blank or background absorbance is to record the spectrum in the vicinity of the band of
interest