or Proton NMR
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or Proton NMR is addressed in a series of topics including
an overview, the number and position of signals, utilization of
peak areas, splitting of signals, the coupling constant, and reading
The basics of instrumentation are introduced in the overview with
a description of the magnetic field requirements, the radio frequency
needed, and the impact on a nucleus sensitive to these requirements.
The concept of alignment of the nucleus with or against an applied
magnetic field is considered, as is the impact of radio frequency
of 60 mHz or 100mHz on that alignment. Terms such as shielded and
deshielded are introduced as is the standard, tetramethyl silane.
Since protons with identical environments will absorb at the same
magnetic field strength, but protons with different environments
absorb at different field strengths, the concept of number of expected
signals is developed. Students are led through a series of compounds
to help them predict when the proton environments will differ.
The impact of electronegative groups on the chemical shift is introduced
to help the student understand where signals are expected to appear.
Proximity to an electronegative group and the relative extent of
deshielding are correlated. The deshielding effects of aromatic
and unsaturated structures are also correlated with position of
To determine the number of protons represented by the various signals,
it is necessary to develop the information to be gained from the
area under the respective peaks. Spectral examples frequently include
the electronic integrator and it is important that the way in which
relative numbers of protons can be determined from these integrator
signals be described.
Splitting patterns are addressed extensively and the reason for
the N+1 number of peaks explained. Students learn how to predict
the number of protons represented by each set of peaks and to logically
determine which groups are adjacent. The concept of the coupling
constant, J, is addressed, particularly from its use in determining
cis and trans orientations and to identify signals from groups generating
splitting patterns of neighboring groups.
A series of five solved problems help the student recognize classic
patterns such as the isopropyl group, as well as a few specific
functional groups. Splitting and position of signals are shown for
disubstitution patterns for benzene. How to recognize overlapping
signals is mentioned and signal symmetry stressed. The way in which
spectra combination such as IR and NMR can be used for identification
of unknowns is used in several examples. The classes
of compounds addressed prior to the NMR study are included in this
unit. Future classes studied each contain a section of spectral