ISSN:
1573-9171
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Conclusions 1. According to MNDO quantum chemical calculations, the reaction of the episulfonium ion with neutral nucleophiles X (X=NH3 and HCN) is facilitated in the presence of a methyl group at the C* atom under attack (opening in accordance with Markovnikov's rule) and is hindered in the presence of a methyl group on the adjacent C atom (opening contrary to Markovnikov's rule). Conversely, SN2 substitution of protonated alkylthiols by the same nucleophiles X is retarded upon introduction of a methyl group at the reacting atom C*. 2. Opening of the C-substituted episulfonium ion in both directions can go through the same pre-reaction complex in which the nucleophile is coordinated approximately at the center of the basal C-C bond. Opening contrary to Markovnikov's rule also can go through an alter-native pre-reaction complex in which the nucleophile is coordinated at the unsubstituted C atom. 3. Analysis of Ea and the enthalpy of reaction δH using the Marcus equation allows us to explain the apparent anomaly in the behavior of Ea upon substitution of episulfonium ions.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00978436
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