How to Handle Equivalence

Question :

Just a quick question about iNMR: I understand that if you want to enter dipolar couplings in your spin simulation module, you can use the lower triangle (after activating anisotropic option). However, there is something I do not fully understand. For example, let’s take a CH3-CH2- spin system. Better still, a A3B2 system. In your dialog you can enter just two spin groups A and B with n=3 and n=2 respectively and also JAB coupling. So far, so good. However, in equivalent groups in oriented systems, the J's remain 'invisible' but the D's not - they are measurable. So this means that the internal D's in equivalent groups must also be specified. Is this possible in iNMR? If it is so, how is it handled?

Answer :

Declare the A3B2 system using 5 rows, as shown by the picture, then add the dipolar couplings:


Whenever a parameter is repeated, for reason of equivalence, you should use literal references. In this way you have 2 chemical shifts and 1 coupling constant, instead of 5 chemical shifts and 6 coupling constants. A single parameter can also be shared between two different spin systems.

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