simulated NMR spectra

NMR spectra with Spin

Motivation!


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
nmr1.gif

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.
nmr1220.gif

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.