This simulates the X-part of an ABX or AMX going to an A2X system. One such system was reported by Rumpel and Limbach (J. Am. Chem. Soc. 1989, 111, 5429). Here the protons are coupled to only one N at low temperature and to 2 Ns at high temperature due to reversible proton transfers. The X part is the proton, the AM parts are the two 15N nuclei To simulate this sytem, set the parameters as shown (this is not the simulation reproduced below). The drawings in this help topic were prepared with PLT.
The AB part can be strongly coupled (as in the spectrum below, for which VAB = 4 and JAB =12 Hz. The program performs a four-spin simulation of the four exchanging lines (pairwise lines 10/11 and 14/15). The two non-exchanging lines 9/12 are simulated as singlets.
To simulate an AMX system (where the X part has only 4 lines, of which only the middle two change) simply set Vab to a large number (10000 Hz). For such systems only a two spin exchange of the two central lines is performed.
Below is a sample simulation of an ABX system:
