They are no big science, rather, we might call them recreational NMR, in the same sense in which one uses the term in Math. The geometric rules applicable to the iso(AB) quartet of spectral peaks are possibly stated here publicly for the first time. As the work proceeds, the articles will get updated, especially for what regards hypertext links and comments like this one. With time, these gaps will be closed, making the Know Thy Spins series a self-coherent, closed exposition of the coupled spin-systems topic. Also, I take the iso(AB) peak frequencies and intensities for granted, relying on the many textbooks in which they are derived. Possible alternatives would be axo(AB) for axially oriented systems, spd(AB) for solid powder, and scr(AB) for a single crystal. The notation iso(AB) indicates a coupled AB spin system composed of two spin 1/2 nuclides under the isotropic rapid-tumbling conditions (liquid-phase high-resolution spectroscopy). Temporary note: This is the first article in the Know Thy Spins series and, in a sense, it starts in the middle of the topic. It is somewhat surprising that, as far as I know, the geometric properties of the AB quartet were never pointed out in NMR textbooks. This is certainly the best known and most frequently encountered case of a coupled spin system and there is no doubt that any NMR spectroscopist should know its properties by heart. It lists some of the generic characteristics of a coupled AB system composed of two spin 1/2 nuclides and points out the simple geometrical relations between the frequencies, intensities and NMR parameters of its four spectral peaks under standard liquid state conditions (isotropic environment, fast molecular tumbling). This article is part of the Know Thy Spins series. via DOI: 10.3247/sl2kts08.001 Other NMR/MRI articles in Extra Byte, Via R.Sanzio 22C, Castano Primo, Italy 20022
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