Small-ring compounds—XXXVIII: Calculations of the relative stabilities of intermediates in the interconversion reactions of cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl derivatives by the LCAO method
✍ Scribed by M.E.H. Howden; John D. Roberts
- Publisher
- Elsevier Science
- Year
- 1963
- Tongue
- French
- Weight
- 695 KB
- Volume
- 19
- Category
- Article
- ISSN
- 0040-4020
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✦ Synopsis
The simple LCAO method with corrections for angle strain indicates that bicyclobutonium cations are likely to be more stable than homoallylic cations. The reverse is predicted to be true for the corresponding free-radical and anionic derivatives. The results are in accord with experiment.
THE very considerable differences between the character of the interconversion reactions of cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl derivatives in processes where carbonium ion intermediates are expected to be important and those which involve free radicals or carbanions 2 has been rationalized qualitatively on the basis of molecular orbital theory. 3'2h It was the purpose of the present investigation to determine whether or not the qualitative conclusions would be supported by calculations along the general lines laid down by Simonetta and Winstein. 4 In brief, the problem has been to explain why cyclopropylcarbinyl, cyclobutyl, and allylcarbinyl derivatives are interconverted one to the other with extraordinary ease in carbonium ion reactions while only cyclopropylcarbinyl and allylcarbinyl derivatives are interconverted in free-radical and anion reactions and then not nearly so easily. The cyclobutyl derivatives appear to react normally in the latter types of reactions. The cationic reactions have been explained in terms of intermediates with nonclassical "bicyclobutonium" structures (I) 2b while the C H2---~.---T. C H C.H z ....