Remote Stereoelectronic Effects

Stereoelectronic Effects A Bridge Between Structure and Reactivity, First Edition. Igor V. Alabugin. 2016 John Wiley Sons, Ltd. Published 2016 by John Wiley Sons, Ltd. 

One of the challenges in understanding stabilizing consequences of remote orbital interactions is to differentiate them from inductive and field effects. This is often a difficult task that can lead to controversies unless one can rule out iuductive coutributious and evaluate field effects by analyzing conformational dependence of stabilities and reactivities. 

---

Polar interactions and/or (remote) stereoelectronic effects (Section 4.5.1.1.3.). 

The importance of specific orbital alignments in the TB propagation of remote stereoelectronic influences can be assessed directly by structure-sensitive spectroscopic techniques. The results of many such studies have been summarized as various effects or rules that express the dependence on geometrical factors, such as the all-trans zig-zag or W pattern of skeletal bridge bonds. Such a W-effect 105... 

Stereoelectronic effects that cannot be viewed as dipole-dipole interactions most probably operate in many concerted epoxidations, however, they are mostly difficult to identify unambiguously because their influence is modest and easily masked by steric or polar effects they can be visualized in Hammett-type correlations by a series of compounds differing only in remote substitution125-127 or substitution with substituents in the plane of the double bond208. 

Stereoelectronic effects of various remote substituents on the basicity of the carbonyl is yet another intriguing question. Electronic effects of remote substituents have been postulated to be responsible for stereoselective additions to carbonyls in rigid adamantanone systems. If present, such stereoelectronic effects would similarly be expected to bias the energetics and structural features of Lewis acid complexation. 

The asymmetric induction cannot be explained simply by steric interaction because the R group in the aldehyde is far too remote to interact with the tartrate ester. In addition, the alkyl group present in the tartrate ligand seems to have a relatively minor effect on the overall stereoselectivity. It has thus been proposed that stereoelectronic interaction may play an important role. A more likely explanation is that transition state A is favored over transition state B, in which an n n electronic repulsion involving the aldehyde oxygen atom and the /Mace ester group causes destabilization (Fig. 3-6). This description can help explain the stereo-outcome of this type of allylation reaction. 

In organic chemistry it is well known that a substituent directly linked to a reaction center has a profound effect on the latter s reactivity. The influence of a remote substituent has also received much attention as more organic molecules are being scrutinized. Thus, neighboring group participations in solvolysis are generally observed. Certainly, the full attribution of a substituent must be the sum of electronic, steric, and stereoelectronic factors. 

---