The kinetic anomalies observed in the formation of small ring systems explained by sigma-assistance and sigma-resistance. Part 4. Carbanion cyclizations
- 1 January 1985
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 9,p. 1355-1360
- https://doi.org/10.1039/p29850001355
Abstract
Cyclization of carbanions to give cyclopropane, cyclobutane, and cyclopentane derivatives shows a behaviour that deviates from that predicted by the Ruzicka hypothesis. This adds to the anomalies, generally observed in the formation of 3-, 4-, 5-, and 6-membered saturated ring systems, i.e., the enthalpy of activation for the formation of the odd-membered rings is consistently found to be lower than that of the less strained next higher even-membered ring. MNDO calculations were performed on the reaction profiles of the carbanion cyclizations for n= 3,4, and 5. The results of these calculations support the earlier conclusion that the anomalies in the ΔH‡ values can be adequately explained by the influence of sigma-assistance and sigma-resistance (i.e., by rules for σ-systems analogous to those described extensively for π-electron systems), mediated by through-bond interaction between the reacting centres.Keywords
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