Ethyl chloride, molecular orbitals

The electrophilic nature of sulfuryl chloride is validated in a study on the chlorination of anthracene derivatives the observed substituent effects conform well with molecular orbital modeling859. Chlorination of ethyl 3,4,5-trialkylpyrrole-2-carboxylates results in a substantial amount of / -side-chain chlorinated products in addition to the expected a-side-chain chlorination860. This has been ascribed to the electrophilic nature of the reagent861 and the mechanism proposed involves an allylic migration of the halogen from the a-sigma adduct to the adjacent / -side chain. 

Hiberty40 used the single determinant ab initio molecular orbital theory to study the unimolecular HC1 elimination from ethyl chloride. The calculations of three potential energy surfaces corresponding to -elimination, planar //-elimination, and nonplanar anti-elimination were performed and the dehydrochlorination process was predicted to be syn, and to proceed via a planar four-membered transition state. According to these estima-... 

Single determinant ab initio LCAO-SCF molecular orbital theory is used throughout this study (6,7), Molecular geometries were optimized with the minimal STO-3G basis set (8,9), and where possible the energy of the final structure was recalculated with the extended 4-31G basis set (9,10), Such a procedure has been shown to provide a reasonable description of the structures and energies of neutral organic molecules (11) and carbocations (12), The potential surface for the concerted elimination of hydrogen chloride from ethyl chloride also has been studied successfully (13) with this technique. 

An example of tunneling in which both the normal and the deuterated species were measured is in HCl or DCl loss from the ethyl chloride ion (Booze et al., 1991). Ab initio molecular orbital calculations (Morrow and Baer, 1988) demonstrated that the HCl loss channel proceeds via a substantial barrier of 1 eV (23 kcal/mol). Yet, the onset for HCl loss occurs at about 0.3 eV. Furthermore, the reaction is very slow (k = 10 sec ). These facts all point to a reaction that proceeds via tunneling. The ab initio calculations provide the vibrational frequencies for both the ion and the transition state, which is located at a saddle point. In addition, they furnish the activation energy as well as the curvature of the barrier (the imaginary frequency). Thus, all the information required in the utilization of the Eckart barrier and equation (7.65) is given. 

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