We report the results of the 13C NMR experiments performed on TMTSF molecules of the organic conductors (TMTSF)2ClO4 and (TMTSF)2ReO4. This investigation has allowed to resolve all individual sites of the organic molecule. Strong and widely distributed enhanced nuclear relaxation rates on different sites of the molecule suggest a picture where Coulomb correlations play a major role for the sites at the corners of the molecule. On the system (TMTSF)2ReO4, continuous variations of the resonance positions are observed when the temperature is decreased down to 182 K, temperature at which the system exhibits a structural transition, leading to a semiconducting state at lower temperature. This experiment constitutes the first observation in direct space of the collapse of the conduction electron density at a metal-semiconductor transition.