Synthesis, conformational and NQR analysis of phosphoric triamides containing the P(O)[N]3 skeleton

New phosphoric triamides with general formula P(O)X3 where X = N-4-methylpiperazinyl (1), N-4-phenylpiperazinyl (2), N-4-ethoxycarbonyl piperazinyl (3), N-2-tetrahydrofurfuryl (4) were synthesized and characterized by 1H, 13C, 31P NMR, IR, Mass spectroscopy and elemental analysis. The molecular structure for compounds 1–4 were obtained by using quantum chemical calculations (HF and B3LYP methods with the 6-31+G∗∗ basis set). Moreover, optimized structures for previously reported 4-FC6H4C(O)NHP(O)X2 phosphoric triamides, X = pyrrolidin-1-yl (5), piperidin-1-yl (6) and hexamethyleneimin-1-yl (7) were obtained using the solid state structure (CIF files) as a starting point for the gas phase computation in which all independent molecules in structures 6 (seven structures) and 7 (two structures) were included. The computed results were in good agreement with the data obtained from the X-ray crystal structures reported earlier. The nuclear quadrupole coupling constants (NQCCs or χs) were calculated about 5.0 and 10.0 MHz for the 17O atoms of PO and CO bonds. For nitrogen atoms bonded to the phosphorus the NQCCs were found in the range between 4.0 and 5.5 MHz, whereas for compounds 4–7, the expected values for amidic hydrogen atoms are near 300 kHz.