Pople Spin System Notation

Refer back to the structure of 1,1,l-trifluoroethane (9-2). Assuming rapid bond rotation, we would designate it as an 

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With an understanding of simple first-order spin systems and of the Pople notations, we can consider the following example. 

The concept of chemical shift equivalence is central to NMR spectrometry. Chemical-shift equivalent (isochronous) nuclei comprise a set within a spin system (Pople notation, Section 3.5). 

If two protons in the same set (i.e., chemical-shift-equivalent protons in the same multiplet) couple equally to every other proton in the spin system, they are also magnetically equivalent, and the usual Pople notations apply A2, B2, X2 etc. However, if two protons in a set are not magnetically equivalent, the following notations apply AA, BB, XX, etc. To rephrase Two chemical-shift-equivalent protons are magnetically equivalent if they are symmetrically disposed with respect to each proton in the spin system. Obviously magnetic equivalence presupposes chemical-shift equivalence. In other words, do not test for magnetic equivalence unless the two protons in question are chemical-shift equivalent. 

For each compound given below (a-o), describe all spin systems (using Pople notation where appropriate), chemically shift equivalent protons, magnetic equivalent protons, enantiotopic protons, and diastereotopic protons. 

Spin systems (collections of interacting nuclei) are often labeled (Pople notation) by assigning a letter from the alphabet to each set of magnetically equivalent nuclei. Nuclei that are close (but not identical) in chemical shift are given letters that are close in the alphabet (e.g., AB). Two nuclei that are chemically equivalent but not magnetically equivalent are assigned the same letter but one letter is primed (e.g., AA ). 

Use Pople notation to identify the types of spin systems that give rise to the spectra shown in Figures 8.20a and b (review problem 8.7). 

Use Pople notation to identify the type of hydro-gen/phosphorus spin system in the structure below ... 

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