I am currently learning about spin-spin coupling mechanisms and have become very confused about the mechanisms by which spin-spin coupling happens in NMR. I understand how we can draw diagrams where the Fermi contact, Pauli interaction and Hund interactions can give us an image of favourable spin states in a spin system. However, I find it challenging to use these diagrams to predict the energies of spin states.
From such diagrams, how can we estimate whether the scalar coupling is positive or negative? For example, for a 1H-12C-12C-1H system or a 19F-12C-1H system.