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430 Chapter 13
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the lowest energy molecular orbital that does not contain electrons.
lowest unoccupied molecular
orbital (LUMO)
mass spectrometry
an instrumental technique that provides a knowledge of the molecular weight and
certain structural features of a compound.
mass spectrum
a plot of the relative abundance of the positively charged fragments produced in a
mass spectrometer versus their
m/z
values.
McLafferty rearrangement
rearrangement of the molecular ion of a ketone that contains a
g
-hydrogen; the
bond between the
a
- and
b
-carbons breaks, and a
g
-hydrogen migrates to the
oxygen.
molar absorptivity
the absorbance obtained from a 1.00 M solution in a cell with a 1.00 cm light path.
molecular ion (M)
the radical cation formed by removing one electron from a molecule.
nominal molecular mass
mass to the nearest whole number.
radical cation
a species with a positive charge and an unpaired electron.
rule of 13
a rule that allows possible molecular formulas to be determined from the
m/z
value
of the molecular ion.
spectroscopy
study of the interaction of matter and electromagnetic radiation.
stretching vibration
a vibration occurring along the line of the bond.
ultraviolet light
electromagnetic radiation with wavelengths ranging from 180 to 400 nm.
UV/Vis spectroscopy
the absorption of electromagnetic radiation that is useful in determining informa-
tion about conjugated systems.
visible light
electromagnetic radiation with wavelengths ranging from 400 to 780 nm.
wavelength
distance from any point on one wave to the corresponding point on the next wave.
wavenumber
the number of waves in 1 cm.