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infrared spectrum
(IR spectrum)
CHAPTER 13
Mass Spectrometry; Infrared Spectroscopy; Ultraviolet/Visible Spectroscopy
Important Terms
absorption band
a signal in a spectrum that occurs as a result of absorption of energy.
auxochrome
a substituent that when attached to a chromophore alters the
l
max
and intensity of
absorption of UV/Vis radiation.
base peak
the peak in a mass spectrum with the greatest intensity.
Beer–Lambert law
an equation that states the relationship between the absorbance of UV/Vis light, the
concentration of the sample, the length of the light path, and the molar absorptivity.
bending vibration
a vibration that does not occur along the line of the bond.
chromophore
the part of a molecule responsible for a UV or visible spectrum.
A
-cleavage
homolytic cleavage of an alpha substituent.
electromagnetic radiation
radiant energy that displays wave properties.
electronic transition
promotion of an electron from its HOMO to its LUMO.
fingerprint region
the right-hand third of an IR spectrum (1400–600 cm
-
1
), where the absorption
bands are characteristic of the compound as a whole.
fragment ion peak
a positively charged fragment of a molecular ion.
frequency
the velocity of a wave divided by its wavelength.
functional group region
the left-hand two-thirds of an IR spectrum (4000–1400 cm
-
1
), where most
functional groups show absorption bands.
the highest energy molecular orbital that contains electrons.
highest occupied molecular
orbital (HOMO)
a plot of relative absorption versus wavenumber (or wavelength) of absorbed
infrared radiation.
L
max
the wavelength at which there is maximum UV/Vis absorbance.
Hooke’s law
an equation that describes the motion of a vibrating spring.
infrared radiation
electromagnetic radiation familiar to us as heat.
infrared spectroscopy
spectroscopy that uses infrared radiation to provide a knowledge of the functional
groups in a compound.