Nomenclature proton chemical shifts

Nomenclature for coupled systems in 1H NMR. The interpretation of a spectrum of a molecule with many hydrogen atoms is simplified when signals that fall into classical cases can be observed. These particular cases are usually classified with a nomenclature that uses the letters of the alphabet, chosen in relation to the chemical shift (Fig. 9.18). Protons with identical or similar chemical shifts are designated by identical letters or neighbouring letters in the alphabet (AB, ABC, A2B2, etc.), while protons with very different chemical shifts are designated by letters such as A, M and X. 

Nomenclature for coupled systems in NMR. Spectral interpretation for a molecule with many hydrogen atoms is easier when sub-groups of signals correspond to classic situations. These particular cases are classified by means of a nomenclature using the letters of the alphabet, selected with respect to the chemical shift (Figure 15.20). Protons with the same chemical environment or chemical shift are caiied equivalent. If the chemical shifts are too little different, the protons are... 

Let us introduce a nomenclature for spin-spin coupling. Consider the molecule where R is nonmagnetic [see structure (I)]. We can discuss the NMR spectrum in terms of chemical shift of protons 1, 2,... 

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