A massive array of special pulse sequences
has been developed, each of which bears its own name in the form
of an acronym based on the underlying idea of spin stimulation.
These sequences produce various kinds of one-dimensional (1D)
and two-dimensional (2D) NMR spectra that reveal through-bond
(scalar) and through-space (dipolar) spin–spin connections among
the NMR-active nuclei. These connections provide an absolute
basis for structure determination: by mapping their magnitude and
topology, mostly between 1H 1H, 1H 13C, 13C 13C and 1H 15N
(as is relevant to bisindoles), the various molecular moieties can
in principle be unambiguously related through chemical bonds
and space, allowing the exact structural identification of organic
molecules without the need to make structural comparisons.
This capability of modern NMR has led to the concept of “ab initio
structure determination”. The development of applied NMR entails
a gradual shift from using relative methods towards placing the
emphasis on absolute ones, which give far more securely established
structures.