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Chapter 13 Spectroscopy
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Chapter 13 Spectroscopy
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Chapter 13 SpectroscopyNuclear magnetic resonance NMR spectroscopy - correct answer-provides information about
the carbon skeleton and the hydrogens attached, transitions occur between spin states of an
atom's nucleus when EM rad causes a molecule to be excited from its most stable state
(ground) to a higher energy state (excited).
Infrared IR spectroscopy - correct answer-presence or signals of functional groups;
transitions occur between vibrational states when EM rad causes a molecule to be excited
from its most stable state (ground) to a higher energy state (excited).
UV-VIS Spec - correct answer-probes the electron distribution, especially in molecules that
have conjugated pi electron system; trans btwn electronic states when EM rad causes a
molecule to be excited from its most stable state (ground) to a higher energy state (excited).
Mass spec - correct answer-provides mol weight and form for both the molecule and
structural units w/in; not based on the absorption of EM radiation, but monitors what
happens when a substance is ionized by collision with a high-E e.
electromagnetic radiation - correct answer-properties of both waves and particles; particles
are photons and each possess an amount of energy referred to as a quantum: E
proportional to freq (v) which is directly proportional to wavelength. E=hv
spectrometers - correct answer-measure the particular photon E absorbed by a molecule
dependent on the molecular structure
resonance - correct answer-the transfer of energy btwn two objects that occurs when their
freq match; the E of photon must = E difference between two quantized states
spectrum - correct answer-a plot of freq and absorption
H NMR spec - correct answer-protons have two spin states 0.5 and -0.5 and is just as likely
to have a spin of either, absorption can only occur when spin states have different E; occurs
when placed into a magnetic field; spin state of magnetic moment aligned with the external
mag field is lower in energy than those that oppose it; the energy diff is prop to the strength
of applied field which must be large to separate and give detectable signal.
free induction decay - correct answer-a composite of decay patterns of all protons in the
molecule after all are excited and as they return to their original orientation.
shielding - correct answer-the net field felt by a proton in a molecule will always be less than
the applied field; deshielded; a more shielded ab RF rad at higher field strength than at
lower.
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