Tetra-tert-butylethylene: An elusive molecule with a highly twisted double bond. Can it be made by carbene dimerization?
- Univ. of Georgia, Athens, GA (United States)
- Institut fuer oekologische Chemie, Oberschleissheim (Germany)
A theoretical evaluation of tetra-tert-butylethylene (1) at the BLYP/DZd level confirms that it should be a stable molecule with a singlet ground state. The synthesis of 1 from two molecules of di-tert-butylcarbene (6) is unlikely. Although the formation of singlet 1 from the triplet {sup 3}B ground state of C (singlet 6 is only 1-3 kcal/mol higher in energy) is highly exothermic ({Delta}H = -73.7 kcal/mol), the barrier {Delta}G{sup {dagger}} = 25 kcal/mol (298 K, 1 atm, BLYP/DZd) for the dimerization is too large to compete with the barrier for intramolecular carbene insertion. The barrier for singlet 6 to yield 1,1-dimethy1-2-teri-butylcyclopropane (12) is only 5 kcal/mol. The CC double bond in singlet 1 is twisted by 45{degree}, and the strain energy is nearly 93 kcal/mol in agreement with molecular mechanics results. Triplet 1 has a nearly perfectly perpendicular conformation at the central CC bond (87{degree} torsional angle), but it is still strained by 42 kcal/mol and is 12 kcal/mol higher in energy than singlet 1. Alkyl substitution decreases the S-T separation of carbenes due to the greater hyperconjugative stabilization of the singlet than the triplet. 65 refs., 8 figs., 5 tabs.
- DOE Contract Number:
- FG05-94ER14428
- OSTI ID:
- 420837
- Journal Information:
- Journal of the American Chemical Society, Vol. 118, Issue 41; Other Information: PBD: 16 Oct 1996
- Country of Publication:
- United States
- Language:
- English
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