Bimolecular elimination reactions stereochemistry

Sunderwirth, S. G., Wood, J. K. Stereochemistry and orientation in bimolecular elimination reactions. Trans. Kans. Acad. Sci. 1967, 70, 17-32. 

It is useful to discuss the stereochemistry of bimolecular elimination reactions in terms of the H—C-C—L dihedral angle (Figure 10.18). Inan anti-periplanar conformation, the dihedral angle H-C 3-Cq,-L is near 180°, while it is near 0° in a syn-periplanar conformation. If dihedral angle is exactly 180°, the conformation is anti-coplanar, while it is syn-coplanar if the dihedral is exactly 0°. An anti-clinal conformation has a dihedral angle of approximately 120°, while a syn-clinal conformation has a dihedral of about 60°. 

Some interesting results have recently been obtained in studies on elimination reactions of esters of hydroxy acids. The mechanism is not fully established, but probably is of the bimolecular type. An especially interesting observation is that sodium iodide promotes the removal of two vicinal sul-fonyloxy groups by a process of cfs-elimination a series of elimination reactions of this type is known in carbohydrate chemistry, but apparently does not yet include an example from which the stereochemistry of the reaction could be deduced. 

PROBLEM 7.85 Select the Bimolecular elimination E)2 reaction. You know about the stereochemistry of the reaction from Section 7.9c. Select the LUMO track for the reaction and observe the starting alkyl halide. Which hydrogens have LUMO character Why ... 

How do the reaction mechanisms and product formation differ when the structure of the substrate and reaction conditions change To begin to unravel the nuances of bimolecular and uni-molecular substitution and elimination reactions, focus on the treatment of bromoalkanes A through D under conditions (a) through (e). Divide the problem evenly among yourselves so that each of you tackles the questions of reaction mechanism(s) and qualitative distribution of product(s), if any. Reconvene to discuss your conclusions and come to a consensus. When you are explaining a reaction mechanism to the rest of the team, use curved arrows to show the flow of electrons. Label the stereochemistry of starting materials and prodncts as R or S, as appropriate. 

The ability of micellized surfactants to catalyze, or inhibit, reactions and to control stereochemistry and product composition, suggests that these agents could have a useful role in organic synthesis. A micelle can speed a desired reaction and inhibit an undesired one, and, for example, cationic micelles can control the ratio of unimolec-ular, Sf l, substitution to bimolecular, E2, elimination [54,55]. Micellization is of great importance in emulsion polymerization, but little use has been made of aqueous micelles in synthesis. 

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