Using three major criteria to evaluate aromaticity of five-member C-containing rings and their Si-, N-, and P-substituted aromatic heterocyclics

Abstract

In this paper, we used bond-length equalization, aromatic stabilization energies (ASE) and nucleusindependent chemical shifts (NICS), calculated with (density functional theory) B3LYP levels at the 6-311 + G * * basis set, to evaluate the aromaticity of a set of 38 five-member planar π -electron aromatic systems: sila-, aza-and phosphaderivatives and their parent systems. The result revealed statistically significant correlations among the above three criteria, and the order of aromaticity of the whole set was: Aza-derivatives rings > Phospha-derivatives rings > Siladerivatives rings > Carbon-containing rings; NICS(0.6) and NICS(0.8) had the same results in evaluating the order of aromaticity in our case.

Stabilization of the Dual-Aromatic cyclo-N5– Anion by Acidic Entrapment

“…In addition, the electronic measures of ELFtotal = 0.713, SA = 210 -10 and RCP ρ curvature = -0.08 indicate that the overall aromaticity of cyclo-N5ˉ is probably stronger than that of the prototypical benzene, as shown by comparison to the corresponding values for benzene: 0.655, 710 -10 and -0.01, respectively. This is consistent with a previous review of polynitrogen compounds 23 and the finding that the presence of N-N, N-P, and P-P bonds can increase the aromaticity of five-membered ring systems [49][50] .…”

“…This is consistent with a previous review of polynitrogen compounds 23 and the finding that the presence of N−N, N−P, and P−P bonds can increase the aromaticity of five-membered ring systems. 49,50 The π-aromaticity of cyclo-N 5 − is well visualized by the local density of states (LDOS) plotted at the minimum energy level of the π-system in Figure 1D, which are spread out over the entire molecule above and below the molecular plane. The bifurcation value for the ELF min-π is 1.000 (Figure 1D), indicating that the basin of the minimum π orbital does not separate (no bifurcation).…”

3-Pyrazolines (2,3-dihydro-1H-pyrazoles): synthesis, reactivity, and physical and biological properties

“…In one paper, the 3-pyrazoline fragment was included in a list of possible effects of pentagonal fragments on aromaticity. 168 Kraka, Cremer et al studied theoretically the reaction of azomethine imine 216 with acetylene to afford the parent 3-pyrazoline 159 (Scheme 55); the level of the calculations was CCSD(T)-F12/aug-cc-pVTZ. 169 The authors represented the 3-pyrazoline ring as being folded about N1•••C4.…”

Application of the Extended HOMED (Harmonic Oscillator Model of Aromaticity) Index to Simple and Tautomeric Five-Membered Heteroaromatic Cycles with C, N, O, P, and S Atoms

“…Consequently, there is no simple relation between the structural descriptors of phospholes and azoles (Figure 7). Phospholes with a PH group (except P5H) are not planar compounds [30,32,89,[98][99][100][101][102][103][104][105][106][107][108][109][110][111]. Phosphorus with H atom in five-membered phospholes is pyramidal, and the bond-angles sum about P is smaller than 360°.…”

“…Note that the PH tautomers can be detected only in the tautomeric mixtures of 1,2,3triphosphole/1,2,5-triphosphole and 1,2,3,4-tetraphosphole/1,2,3,5-tetraphosphole. Their relative Phospholes with a PH group (except P5H) are not planar compounds [30,32,89,[98][99][100][101][102][103][104][105][106][107][108][109][110][111]. Phosphorus with H atom in five-membered phospholes is pyramidal, and the bond-angles sum about P is smaller than 360°.…”