  X-ray four-wave mixing signals generated in the $k_1 + k_2 - k_3$
phase-matching direction are simulated for N1s transitions in para-nitroanline
and two-ring hydrocarbons disubstituted with an amine and a nitroso groups. The
two-dimensional x-ray correlation spectra (2DXCS) provide background-free
probes of couplings between core-electron transitions even for multiple core
shells of the same type. Features attributed to couplings between
spatially-separated core transitions connected by delocalized valence
excitations provide information about molecular geometry and electronic
structure unavailable from linear near-edge x-ray absorption (XANES).
