4 research outputs found
Exploring the Origin of the Generalized Anomeric Effects in the Acyclic Nonplanar Systems
Contrary to the published conclusions
in the literature concerning the origin of the generalized <i>anomeric</i> relationships in open-chain nonplanar systems,
its origin has remained an open question. In order to explore the
origin of the generalized <i>anomeric</i> relationships
in open-chain nonplanar systems, we assessed the roles and contributions
of the effective factors on the conformational properties of methyl
propargyl ether (<b>1</b>), methyl propargyl sulfide (<b>2</b>), and methyl propargyl selenide (<b>3</b>) by means
of the G3MP2, CCSDÂ(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 <b>1</b>–<b>3</b> by the deletions
of the orbitals overlapping from the Fock matrices of the <i>gauche</i>- and <i>anti</i>-conformations. The trend
observed for energy changes in the Fock matrices justify the variations
of the <i>gauche</i>-conformations preferences going from
compound <b>1</b> to compound <b>3</b>, revealing that
the hyperconjugative interactions are solely responsible for the generalized <i>anomeric</i> relationships in compounds <b>1</b>–<b>3</b>. Accordingly, the conclusions published in the literature
concerning the origin of the generalized <i>anomeric</i> effect in the acyclic nonplanar compounds should be revised by these
findings. The Pauli exchange type repulsions (PETR) are in favors
of the <i>gauche</i>-conformations and the variations of
the PETR differences between the <i>gauche</i>- and <i>anti</i>-conformations of compounds <b>1</b>–<b>3</b> correlate well with their <i>gauche</i>-conformations
preferences, revealing that the generalized <i>anomeric</i> relationships in compounds <b>1</b>–<b>3</b> 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