Complete basis set, hybrid‐DFT study and NBO interpretations of conformational behaviors of trans‐2,3‐ and trans‐2,5‐dihalo‐1,4‐dithianes

Abstract

The conformational behaviors of trans‐2,3‐dihalo‐1,4‐dithiane [halo = F (1), Cl (2), Br (3)] and trans‐2,5‐dihalo‐1,4‐dithiane [halo = F (4), Cl (5), Br (6)] have been analyzed by means of complete basis set CBS‐4, hybrid‐density functional theory (B3LYP/6‐311 + G**//B3LYP/6‐311 + G**) based methods, and natural bond orbital (NBO) interpretation. Both methods showed that the axial conformations of compounds 1–5 are more stable than their equatorial conformations but CBS‐4 resulted in an equatorial preference for compound 6. The Gibbs free energy difference (Geq−Gax) values (i.e., ΔGeq–ax) at 298.15 K and 1 atm between the axial and equatorial conformations decrease from compound 1 to compound 2 but increase from compound 2 to compound 3. Also, the calculated ΔGeq–ax values decrease from compound 4 to compound 6. The NBO analysis of donor–acceptor (LP → σ*) interactions showed that the anomeric effect (AE) increase from compound 1 to compound 3 and also from compound 4 to compound 6. On the other hand, the calculated dipole moment values between the axial and equatorial conformations [Δ(µeq−µax)] decrease from compound 1 to compound 3. The conflict between the increase of AE and the decrease of Δ(µeq−µax) values could explain the variation of the calculated ΔGeq–ax for compounds 1–3. The Gibbs free energy difference values between the axial and equatorial conformations (i.e., ΔGax–ax and ΔGeq–eq) of compounds 1 and 4, 2 and 5 and also 3 and 6 have been calculated. The correlations between the AE, bond orders, pairwise steric exchange energies (PSEE), ΔGeq–ax, ΔGax–ax, ΔGeq–eq, dipole–dipole interactions, structural parameters, and conformational behaviors of compounds 1–6 have been investigated. Copyright © 2010 John Wiley & Sons, Ltd.

Complete basis set, hybrid-DFT study, and NBO interpretations of the conformational behavior of 1,2-dihaloethanes

“…We do not know whether the apparent decrease in DG 1 à as calculated by CBS-QB3 in going from the dichloro to the dibromo compound is real or not. We have previously observed suspicious results from this procedure in isolated cases [43], presumably brought in by the empirical corrections used [34].…”

“…r* C2-X , LP 3 X C1 ? r* C2-X ) in compounds 1-4 stability, reactivity, and dynamic behaviors of chemical compounds [37][38][39][40][41][42][43].…”

Conformational Behaviors of 2-Substituted Cyclohexanone Oximes: An AB Initio, Hybrid Dft Study, and NBO Interpretation

“…Calculations at this level are expected to be reasonably reliable, 43 but the important information here lies in the differences between closely related distances, which should be even more accurate. Consideration of the structures of compounds 1-6 gave evidence that in the axial conformations of these compounds, the r C1-N7 bond lengths is significantly longer than that of the corresponding equatorial conformations.…”

“…[28][29][30][38][39][40][41] On the basis of the NBO results, the energy difference between donor (Eσ C2-X9 ) and acceptor (Eπ * C1-N7 ) orbitals [i.e., (Eπ * C1-N7 -Eσ C2-X9 )] for the axial conformations decrease from compound 1 to compound 3 (see Table 2). The strong donor bonding orbital of compound 3 (Eσ C2X9 : −0.50816 a.u.…”

Correlations between hardness, electronegativity, anomeric effect associated with electron delocalizations and electrostatic interactions in 1,4,5,8-tetraoxadecalin and its analogs containing S and Se atoms

“…The anomeric effect which originally denoted the preference of electronegative substituents at the anomeric centers of pyranoses for the axial conformations arises as a result of stereoelectronic interactions [26][27][28][29][30][31][32][33][34][35][36].…”