93754-98-4Relevant academic research and scientific papers
Ring Opening of a Formal Cyclopentylmethyl Radical in the Thermolysis of Di(tert-alkyl)(1-norbornyl)methanols
Lomas, John S.,Briand, Sylvette
, p. 191 - 200 (2007/10/02)
In the thermolysis of di(1-adamantyl)(1-norbornyl)methanol, Ad2NorCOH, 1a, in toluene at 220-265 deg C, C-C bond cleavage within the norbornyl group of the first-formed (1-adamantyl)(1-norbornyl)ketyl radical (by loss of Ad.) leads to ring-opened ketones and several ketonic cross-products.These are isomeric with the secondary alcohol, AdNorCHOH, and with the regular cross-product, AdNorSCOH (S = benzyl), respectively, also present in the product mixture.Formation of the ring-opened thermolysis products is particularly favoured by high temperature and the use of deuteriated solvent, which slows hydrogen transfer from the solvent to the intermediate ketyl radical.The new products are cyclopentane derivatives, formed by cleavage of the norbornyl C(1)-C(2) bond, in agreement with MM2 calculations on the transition states.Self-consistent values for the cage effect have been determined by measuring the extent of 1- labelling of the adamantane formed in toluene and by scavenging the ketyl radical with benzenethiol in toluene.The product composition of the scavenger-free reaction in or toluene has been interpreted by kinetic simulation based on the steady state approximation, a Simplex procedure being used to optimise several rate constants, in particular those for hydrogen transfer from toluene to the ketyl radical and ring opening of the latter.The Arrhenius pre-exponential factor and activation energy are both much greater for ring opening than for hydrogen transfer.
Thermolysis of Highly Congested Tri-tert-alkylmethanols: Strain Energies of Bridgehead Alkyl Radicals
Lomas, John S.
, p. 4291 - 4299 (2007/10/02)
The rate constants and the products of the thermolysis of tertiary alcohols, R1R2R3COH, where Ri is tert-butyl, 1-adamantyl, 1-bicyclooctyl, or 1-norbornyl, have been determined.Apart from the usual secondary alcohols and ketones, the products include new ketones, formed by ring opening of the 1-norbornyl group, and solvent-incorporated alcohols.The activation energies for (t-Bu)-C, Ad-C, Oc-C, and, in one case, Nor-C cleavage are compared with the molecular mechanics calculated strain-energy changes, Δstrain.These latter are based on a simple model of the reaction intermediate where the bridgehead radicals are represented by the corresponding alkanes.Taking the ΔG(excit.)(200 deg C)/Δstrain correlation for t-Bu-radical formation as a reference, one can show that the deviations, ΔΔstrain, of the data for the formation of the other radicals (Ad, 2.4; Oc, 4.0; Nor, 7.7 kcal mol-1) indicate the real difference between the strain energies of the radicals and the alkanes.Analogous ΔΔ(excit.) data for other reactions considered to involve rate-determining radical formation correlate with ΔΔstrain, the slopes ranging from 0.16 to 1.13.The ΔΔstrain values also correlate with solvolysis rate constants of tert-alkyl tosylates, with a slope (ΔΔstrain/ΔG(excit.)(70 deg C)) of 0.36; tentative values for the strain energies of other bridgehead radicals are proposed and compared with the predictions of a radical force field.
