materiały: Stereoelectronic effect

Evidence: 100 • authority: 72

In chemistry, primarily organic and computational chemistry, a stereoelectronic effect is an effect on molecular geometry, reactivity, or physical properties due to spatial relationships in the molecules' electronic structure, in particular the interaction between atomic and/or molecular orbitals. Phrased differently, stereoelectronic effects can also be defined as the geometric constraints placed on the ground and/or transition states of molecules that arise from considerations of orbital overlap. Thus, a stereoelectronic effect explains a particular molecular property or reactivity by invoking stabilizing or destabilizing interactions that depend on the relative orientations of electrons…

Evidence: 53 • authority: 88

Effects on conformation. This chapter examines the effects on conformation. The single most important principle of conformational analysis is that rotation about single bonds is not free, but restricted by energy barriers which depend on the substituents at the ends of each bond. Other things being equal, staggered conformations are preferred, with large, sterically demanding groups antiperiplanar, i.e. as far away from each other as possible. The general orbital interaction demonstrates that (four-electron) interactions between filled orbitals are antibonding, and thus repulsive. These repulsive interactions are largest in eclipsed conformations and minimized in staggered conformations. It…

Evidence: 53 • authority: 92

Acetal Substitution Reactions: Stereoelectronic Effects, Conformational Analysis, Reactivity vs. Selectivity, and Neighboring-Group Participation.. Acetal substitution reactions can proceed by a number of mechanisms, but oxocarbenium ion intermediates are involved in many of these reactions. Our research has focused on understanding the conformational preferences, structures, and reactions of these intermediates. This Account summarizes our observations that electrostatic effects play a significant role in defining the preferred conformations, and that torsional effects determine how those intermediates react. Neighboring-group effects are not as straightforward as they might seem, consider…