Secondary Intermolecular Kinetic Isotope Effects in the Methylene Radical-cis-Butene-d8-cis-1, 2 Dimethylcyclopropane-d8 System

摘要

A study of the geometric and structural isomerization reactions of chemically activated cis-1,2-dimethylcyclopropane-do (dmc-do) and dmc-d8 is reported. Activation was by addition of methylene from the photolysis of ketene at 3200, and 25°, to the double bond of cis-butene-2-do and-d8. The measured intermolecular isotope effects for the geometric isomerization (kg(H)/kg (D)- 3.8) and for one of the structural isomerization (ksp(H)/ksp(D)-4.3) reactions are for the most part, secondary quantum statistical-weight effects. The effect on other structural isomerization processes (ksb(h)ksb(d)-5.2) is a mixed primary-secondary isotope effect. Theoretical calculation of rates and of isotope effects are in fairly good agreement with experimental values.nAnomalous high pressure product compositions in both the do and -d8 systems can be explained by the presence of -29% triplet methylene radical reaction at high pressures. The addition of oxygen altered the product composition so as to indicate the removal of the triplet methylene reaction, Our earlier work (ref. 10) on the Isotope effects in singlet methylene radical C-H insertion and C-C addition reactions with cis-butene-2 has been extended.nCalculations of the geometric isomerization rates of l,2-cyclo propane=d2 and l.2-dimethylcyelopropane have been made and are compared to the existing data in thermal and chemical activation systems.