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

作者：Nori Shargh Davood; Boggs James E^*

来源：Journal of Physical Organic Chemistry, 2011, 24(3): 212-221.

DOI：10.1002/poc.1728

• ab initio
• anomeric effects
• dihalo-1,4-dithiane
• molecular modeling
• NBO
• stereoelectronic interactions

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), CI (5), Br (6)] have been analyzed by means of complete basis set CBS-4, hybrid-density functional theory (B3LYP/6-311 + GB3LYP/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 (G(eq)-G(ax)) values (i.e., Delta G(eq-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 Delta G(eq-ax) values decrease from compound 4 to compound 6. The NBO analysis of donor-acceptor (LP -> sigma*) 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 [Delta(mu(eq)-mu(ax))] decrease from compound 1 to compound 3. The conflict between the increase of AE and the decrease of Delta(mu(eq)-mu(ax)) values could explain the variation of the calculated Delta G(eq-ax), for compounds 1-3. The Gibbs free energy difference values between the axial and equatorial conformations (i.e., Delta(ax-ax) and Delta G(eq-eq)) of compounds 1 and 4, 2 and Sand also 3 and 6 have been calculated. The correlations between the AE, bond orders, pairwise steric exchange energies (PSEE), Delta G(eq-ax), Delta G(ax-ax), Delta G(eq-eq), dipole-dipole interactions, structural parameters, and conformational behaviors of compounds 1-6 have been investigated.

• 出版日期2011-3