Stereoelectronic Effects in N−C−S and N−N−C Systems: Experimental andab InitioAIM Study

Abstract

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 rho( 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.

Synthesis, crystal structure, and interconversions of new N-aryl-1,3,5-dithiazinanes, 1,3,5-thiadiazinanes, and 1,5-dithia-3,7-diazacyclooctanes

“…The strength of the stereoelectronic interaction can be estimated from the change of the C-S bond distance, which in the N-CH 2 -S system is 1.814 Å in the absence of the stereo electronic interaction and can increase to 1.860 Å if it is present. 16 Based on the data given in Table 4, a conclusion can be drawn that the conjugation between the lone pair of electrons on the nitrogen atom and the phenyl ring is present in all the compounds studied (the N-C arom bond is shorter than the value of 1.430 Å characteristic of (Alk) 2 N sp 3 -C arom ). 17 At the same time, this conjugation does not lead to a noticeable flattening the nitrogen atom (the nitrogen atom comes out of the plane by 0.15-0.28 Å).…”

1-Aryl-2-nitro-3-trichloromethylaziridines: synthesis and structure

“…An analysis of the electron density distribution func tion (ρ(r)) based on the results of MP2 calculations revealed the bond critical points (3,-1) (CP (3,-1)) not only for all expected bonds but also for the intramolecular C (4) 122.22 (14) 123.11 (9) 123.41 (12) 122.24 (12) 122.46(12) C(5)-N(1)-C (2) 126.19 (4) 125.82 (14) 123.85 (9) 125.12 (12) 124.69 (12) 124.45 (12) 115.98 (4) 116.14 (14) 115.83(10) 119.12 (13) 119.05 (12) 116.32(13) O(1)-N(2)-C (2) 118.61 (4) 118.82 (14) 118.77 (9) 115.64 (15) 116.00 (12) 118.43(13) N(1)-C(2)-C (3) 58.80 (3) 59.12(11) 58.73 (7) 117.60 (13) 118.69 (12) 58.72(9) N(1)-C(2)-N (2) 119.64 (4) 119.40 (14) 118.39 (9) 58.61 (9) 58.81 (9) 117.72(12) C(3)-C(2)-N (2) 114.68 (4) 114.65 (14) 114.93 (9) 116.42 (14) 116.51 (12) 115.01(13) N(1)-C(3)-C (2) 58.83 (3) 58.83(11) 59.28 (7) 59.04 (9) 59.19 (9) 59.48(9) N(1)-C(3)-C (4) 118.83 (4) 118.57 (15) 118.25 (9) 116.19 (13...…”

“…These values are in qualitative agreement with the dependences revealed previously for the stereoelectronic N-C-S interactions. 15 Thus, the Cl(2) and Cl (3) atoms acquire an additional negative charge. It should be noted that the higher charge is observed for the chlorine atom involved in the interaction with the more donor (NBO data) C-C bond of the aziridine moiety.…”

“…However, the change in the energy for the Cl(2) and Cl (3) atoms estimated by the integration of the local electron energy density (h e (r)) over the atomic basins appeared to be oppo site to the change in the charge (+2.4 and +2.8 kcal mol -1 with respect to the energy of Cl (1)) for the Cl (2) and Cl(3) atoms, respectively), which is inconsistent with the correlations found for the N-C-S system. 15 This can be attributed to the fact that the stereoelectronic interaction is very weak and, consequently, the relative energies of the Cl(2) and Cl (3) The rotation barrier can serve as another independent estimate of the energy of stereoelectronic interactions. The potential surface scan along the Cl(1)-C(4)-C(3)-N(1) torsion angle coordinate by the density functional theory at the B3LYP/6 311g(d) level gave the rotation barrier of the CCl 3 group equal to 4.1 kcal mol -1 .…”

Insertion of carbon disulfide and the nitrile group into the diaziridine ring of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes in ionic liquids catalyzed by BF3 · Et2O

“…24 The N(1) atom has a flattened configuration (the sum of the van der Waals angles is 359.7(1)°) due to its conjugation to the C=O group, which also leads to an elongation of the C (6) Presumably, in addition to the inductive effect of the CN group, the stereoelectronic interaction of the lone electron pair of the N(2)C(13)H(13A) fragment, which partially compensates the charge on the hydrogen atom, is one of the factors responsible for the strong inter actions with the involvement of this hydrogen atom. 25 Since ionic liquids were used as the reaction medium, one of the purposes of the present study was to investigate the regeneration of ionic liquids with the aim of their repeated use. For this purpose, we performed several re peated syntheses of compounds 7b and 8e,g in the ionic liquid [bmim] [BF 4 ] according to the standard procedure, but with the use of the triple regeneration of the ionic liquid by the careful evaporation in vacuo of the solvents after extraction.…”