This section supplements the discussion in Chapter 21 on NMR spectra. It is also an integral part of Lab 3, Nuclear Magnetic Resonance.
You can change the relative chemical shift d and the spin-spin coupling constant J. The chemical shift is expressed in parts per million of the nominal resonance frequency, and you are shown the product of d and the nominal frequency (in Hz). The J constant is also expressed in Hz, and the various limiting cases of the spectrum discussed in the lab handout come from comparing these two frequencies.
The top spectrum shows the entire two-spin spectrum, centered on the graph. Frequencies are expressed as positive or negative shifts from this center frequency.
The bottom spectrum shows only the high-frequency two transitions of the full spectrum (the frequency range denoted by the blue bar in the top spectrum). This magnified portion is useful for those parameter choices that lead to line separations that are difficult to see in the full spectrum.
The y axis in both graphs is an arbitrary signal strength, S, but the relative transition intensities are accurate. The line shapes in both graphs are artificially chosen for good display; they may not be the same in both graphs, and they may not correspond to your experimental spectra.