Hyperconjugative interactions are the main responsible for the anomeric effect: a direct relationship between the hyperconjugative anomeric effect, global hardness and zero-point energy

The contribution of non-classical CHax⋯OC hydrogen bonds to the anomeric effect in fluoro and oxa-methoxycyclohexanes

“…The most widely discussed explanation for the anomeric effect invokes hyperconjugation. 1,2,3,4,5 In the case of 2methoxytetrahydropyran 1 this is facilitated in the axial conformer where there is an antiperiplanar relationship between a lone pair of the (endo) ring oxygen 2p-type and the antibonding orbital of the exocyclic C-O bond (nO → *CO overlap) (Figure 1a). This is reciprocated by hyperconjugation between a lone pair of the (exo) methoxyl oxygen and the endocyclic bond (nO → *CO overlap).…”

A Computational Investigation of the Uncatalysed and Water-Catalysed Acyl Rearrangements in Ingenol Esters

“…To rationalise this it is necessary to consider the roles of destabilising electrostatic interactions in the anti-staggered conformation and stabilising stereoelectronic interactions in the gauche-staggered conformation in the transition structures. 84,85,86,87,88,89,90,91,92,93 These can be invoked to explain the notable stereoselectivity of the reaction path of the uncatalysed acyl rearrangements in the ingenol ester. As illustrated by figure 10a electrostatic repulsion of 18 aligned dipoles in the transition structures with anti-staggered conformation has a destabilising effect.…”

“…Such an interaction is less accessible in the anti-staggered conformation due to unfavourable orbital orientations ( Figure 10b). 84,85,86,87,88,89,90,91,92,93 While these interactions in systems subject to an anomeric effect have been the topic of numerous studies, the largest focus has so far been on the study of ground state structures. 68,86,89,91,94 As hyperconjugation is known to stabilise transition structures 66,67,70,95,96 and since anomeric hyperconjugation has been found to be amplified in transition structures, 67,97 the relative magnitudes of the hyperconjugative interactions between the X- 19 oxygen lone pairs and carbonyl antibonds in the anti-and gauche-staggered transition structures of the acyl migrations were studied via second-order perturbation analysis.…”

Assessing the effective factors affecting the conformational preferences and the early and late transition states of the unimolecular retro-ene decomposition reactions of ethyl cyanate, ethyl thiocyanate and ethyl selenocyanate

“…antibonding orbitals, which is in accordance with the Mulliken (or Wolerg-Helmholtz) approximation. 47,48 Based on the Mulliken (or Wolerg-Helmholtz) approximation, the desirable orbital overlapping between the donor and acceptor orbitals are reachable by substantial adjustments of their offdiagonal terms.…”

“…It is worth noting that the procedure mentioned above is an efficient approach and can be performed to evaluate the role and contributions of some specic hyperconjugative interactions on the conformational properties of chemical compounds. 28,29,47 calculations [54][55][56] instead of MP4 for the basis set extension corrections, and also the MP2 method with the 6-311++G** basis set [57][58][59][60][61][62][63][64][65] on all atoms (MP2/6-311++G**) were performed to optimize the structural parameters of the gauche-and anticonformations and the transition state structures of the unimolecular retro-ene decomposition and cyanate / isocyanate isomerization reactions of compounds 1-3 and also to calculate their corresponding electronic energies and thermodynamic functions together with the GAMESS US package of programs. 66,67 The natural bond orbital (NBO) interpretation was performed to examine quantitatively the impacts of the plausible hyperconjugative interactions and the Pauli exchange-type repulsions on the conformational and structural properties and also the potential energy surfaces of the retro-ene decomposition of compounds 1-3.…”