This is a 60 MHz spectrum of Phenyloxirane ('Styreneoxide'). The program 'Spin' needs as
input the chemical shifts of the three protons (absolute, i.e. Dd*MHz
in cycle/s) and the three spin-spin coupling constants (cycles/s). It then generates the
spin hamiltonian in Fz block matrix form and diagonalizes the matrices to
obtain the spin eigenvalues. With the help of the transition matrices the spectrum
(frequencies and intensities) is computed and saved on disk. Now, you can start NMRplot to
either show a stick or a line plot of the computed spectrum as on this and the following
figures. The program can handle up to 8 spin-systems and is extremely fast. See the next couple of examples
Another three spin system: Acrylonitrile. This time the ABC case does not yield to a first
order analysis because the coupling constants are of the same size or larger than the
differences of the chemical shifts in this 1.4 Tesla/60 MHz spectrum. All 15 possible lines are
produced, including those forbidden in first order.
If the spectrum is taken with a magnet of 5.2 Tesla/220 MHz Acrylonitrile becomes a simple AMX system
with completely separated signals of the three protons, see integral trace, and showing
the 12 lines allowed in first order with a tiny peak of a 13th transition (at 84 c/s in fig.). Program spin can easily
simulate these features in agreement with experiment.
This 100 MHz
spectrum of dry Ethanol shows (from left) a triplet for the -OH proton, two
overlapping quartets for -CH2-, and another triplet for -CH3.
This is only approximately valid, since the lines are more complex under higher resolution
as the inset for the methylene protons shows. This has been produced from the same data
with the help of the magnifier feature of NMRplot.
As soon as some water and a trace of acid is added to ethanol the spectrum becomes simpler
due to the rapid proton exchange of the hydroxylgroup with the environment. The leftmost
signal is now a single peak and the other features have simplified as well.