Pople notation

The Pople nomenclature is named after the Nobel Prize for Chemistry John Pople and allows a simple representation of repeated emerging spin coupling patterns in NMR. It is derive by symmetry considerations and provides information about how many spectral lines and with what multiplicity in the NMR spectrum to be expected.

Definitions

It is defined for each magnetic one letter:

• A, B, M, N, X, Y

Is the chemical shift of two nuclei similar, one writes:

• AB, MN, XY
• A2B2, AB3, ...

The chemical shift is significantly different, as shown by the use of letters in the alphabet that are far away from each other:

• AM, AN
• A2M, AM4, ...

The chemical shift is orders of magnitude different, this is so indicated:

• AX, AY
• A2x2

With the same chemical shift but coupling with each other to write:

• AA ' XX'
• AA'XX '

If can be converted into each other by a symmetry operation two chemically equivalent nuclei, while all other spin-bearing atoms are left alone, they do not couple.

Examples

A) 1,1- difluoroethene coupling the identical proton shifts (chemical equivalence ), but with each other yet. Reason: When two proton nuclei are chemically equivalent, but coupled together, it is called a AA ' spin system. Are there two more spin -bearing atoms are present, eg Fluorine, one has additionally XX '. The overall system is thus AA'XX '. Consequently, the user has an octet in the 1H NMR.

B ) Methane: The four methane protons do not couple with each other, you have an A4 system. Result: you get a singlet in the H- NMR.

C ) In the case of 1,1- dichloroethene has an A2 system. Reason: There is a symmetry operation ( here: the mirror plane ), which leads the two protons into each other. The chlorine atoms are even moved but are not spin -supporting. Result: You have a singlet in the 1H NMR.