¹H‐NMR Spectra of the AA′XX′ and AA′BB′ Type – Analysis and Classification

It is shown how the secular determinant for the general four‐spin case can be greatly simplified in the case of NMR spectra of the AA′XX′ and AA′BB′ type on the basis of molecular symmetry and with the aid of the so‐called X approximation. The methods for the direct analysis of these spectra are presented, and the relations between the type of spectrum and the chemical structure are discussed in detail for selected examples. In an appendix, parallels are pointed out between the formalism of the Hückel MO theory and the calculation of the eigenvalues and eigenfunctions of nuclear spin systems.