Dear all,

My first question here, I hope that someone can help!

In a paper describing a method to measure diffusion using multiple-quantum coherences (Zax, J.Chem.Phys, 1983, 78, 6333), I found the following statement:

"Multiquantum NMR experiments have the following advantages for the study of molecular diffusion: (...) for N coupled protons the N-quantum transition is free of couplings. The possible limitations are that the spectrum must show splittings from scalar, dipolar or quadrupolar coupling; and that, except for double-quantum excitations, there is a loss of sensitivity because of inefficient transfer of magnetization."

Regardless of the context of the article, why is the N-quantum transition free of couplings? And why then does it show splittings?