No abstract

Brown, J. Chem. SOC. 6, 1586 (1970).An admittedly crude estimate of the nonconcerted process (-42 kcall mol) was obtained by consideration of the energy difference between 2 and 9 ( L 3 kcallmol based upon no detectable concentration of 9) and the energy required to cleave the C-1, C-14 bond in 9 [C-C bond (84) allylic stabilization (2 X 11)"strain released in transition state (23)];'8 whereas, the observed activation energy is -32 kcal/mol. While it can be argued that a greater amount of strain exists in 9 than in norbornene (the value used in the above estimate), we are only concerned with the amount of strain that is released at the transition state and that the product is also considerably strained. The maximum release of strain energy = strain of 9strain of 1 and, considering the structural similarities of 9 and 1. should be fairly approximated by the strain of norbornene.D. M. Golden and S. W. Benson, Chem. Rev., 69, 125 (1969). and earlier references cited therein; J. A. Berson and E. serve the exchange of only a single ring proton upon reaction of mxylene with D20 under ICR conditions. This would seem to imply that the CH, ion is the true ground state form of a protonated aromatic, an ObSeNation which is at odds with the results of the STO-3G calculations, whichsuggests the energy of such a structure to be 2.0 kcallmol above the ion proposed here. We can think of no explanation for this discrepancy. . For the initial account of our application of ion cyclotron resonance spectroscopy to the determination of equilibrium isotope effect, see (b) I All reactions were carried out a t 15 kbar and room temp; the concentrations of the reactants were nominally 3 M in methylene chloride. ' Yields are based on distilled materials unless indicated otherwise. Reaction conditions have not been optimized; in addition to product, only starting materials were present at the conclusion of the reaction. Satisfactory analytical and spectral data were obtained for each product. A substantial amount of polymeric material was also produced. f In this case R3 is cis to Y in dienophile (eq I ) . R Crude yield; NMR spectrum indicated material to be of very high purity. Product reversed to starting materials during attempted distillation. See text for stereochemistry of adduct.

No abstract

No abstract

No abstract