Stereoelectronic Effects in N−C−S and N−N−C Systems: Experimental and <i>ab Initio</i> AIM Study

The energy of stereoelectronic interactions in N−C−S and N−N−C systems in tetrahydro[1,3,4]thiadiazolo[3,4-c][1,3,4]thiadiazole was estimated by means of R. W. Bader’s quantum theory of “atoms in molecules” (AIM) and natural bond orbital analysis (NBO). The results were compared with those obtained by analysis of ρ(r) derived from high-resolution X-ray diffraction data. The analysis of the data obtained allowed one to find a correlation between geometric characteristics of the stereoelectronic interactions, NBO mixing energies and the AIM properties of atoms. Significant variations of nitrogen atom atomic basin populations in different conformers were explained by sterical interactions between their electron lone pairs.