Exploring the Origin of the Generalized Anomeric Effects in the Acyclic Nonplanar Systems

Abstract

Contrary to the published conclusions in the literature concerning the origin of the generalized anomeric relationships in open-chain nonplanar systems, its origin has remained an open question. In order to explore the origin of the generalized anomeric relationships in open-chain nonplanar systems, we assessed the roles and contributions of the effective factors on the conformational properties of methyl propargyl ether (1), methyl propargyl sulfide (2), and methyl propargyl selenide (3) by means of the G3MP2, CCSD(T), MP2, LC-ωPBE, and B3LYP methods and natural bond orbital (NBO) interpretations. We examined the contributions of the hyperconjugative interactions on the conformational preferences of compounds 1-3 by the deletions of the orbitals overlapping from the Fock matrices of the gauche- and anti-conformations. The trend observed for energy changes in the Fock matrices justify the variations of the gauche-conformations preferences going from compound 1 to compound 3, revealing that the hyperconjugative interactions are solely responsible for the generalized anomeric relationships in compounds 1-3. Accordingly, the conclusions published in the literature concerning the origin of the generalized anomeric effect in the acyclic nonplanar compounds should be revised by these findings. The Pauli exchange type repulsions (PETR) are in favors of the gauche-conformations and the variations of the PETR differences between the gauche- and anti-conformations of compounds 1-3 correlate well with their gauche-conformations preferences, revealing that the generalized anomeric relationships in compounds 1-3 have also the Pauli exchange-type repulsions origin. The resemblance between the preorthogonal natural bond orbitals (that are involved in the hyperconjugative interactions) and their corresponding molecular orbitals have been investigated.

Study of influence of anomeric effect on conformational preferences using hybrid density functional theory (DFT) and natural bond orbital (NBO) interpretation

“…44 So far, comprehensive research been conducted on the NBO calculations. 42,[45][46][47] The NBO interpretations were used to investigate quantitatively the stabilization energies (E2) associated with the electron delocalizations in the axial-and equatorial-configurations of compounds A-D. It is worth noting that the NBO interpretation is a sufficient approach to investigate quantitatively the impacts of the electron delocalizations on the reactivity and dynamic behaviors of chemical compounds.…”

Theoretical exploration to the significance of n(S)/n(O) → σ* (C-COOMe) stereoelectronic interactions

“…1,2 The stability of the conformations in X-C-Y (where X has one or more non-bonded lone pair of electrons and Y possesses an electronegative group like -OR, -CRN, -CRCR, and -F) arises due to electron transfer between the filled (n or s) and unfilled (s*) orbitals. [3][4][5][6] Electron delocalization has been achieved more effectively when the best donor orbital is oriented antiperiplanar to the best acceptor orbital. 7 This subtle stereoelectronic effect is governed by the interplay between kinetic, thermodynamic and solvation effects.…”

Structural, Electronic, Reactivity, and Conformational Features of 2,5,5-Trimethyl-1,3,2-diheterophosphinane-2-sulfide, and Its Derivatives: DFT, MEP, and NBO Calculations

“…The conformational equilibrium is influenced by stereoelectronic interactions, which have long been recognized [11,12]. However, Praly and Lemieux define anomeric effect (AE) based on a difference between equatorial (eq.)…”