Kinetics of hydrogen and deuterium atom abstraction by methyl radicals from ethylene diamine and ethylene diamine-N-d4

Abstract

The rates of hydrogen-abstraction by methyl radicals from the two different sites in ethylene diamine have been measured by using the isotopically different species NH₂CH₂CH₂NH₂ and ND₂CH₂CH₂ND₂. Arrhenius parameters (based on a value of 10^13.34 cm³ mole^–1 sec^–1 for the dimerization of methyl radicals) have been determined as follows: [graphic omitted] At 150°C the methylene groups are 2.5 times as reactive as the amine groups.

In work with unlabelled compounds, the observed rate constant is the sum of two or more separate rate constants. In an appendix, the non-linearity of Arrhenius plots caused by simultaneous reactions with different activation energies is investigated. The departure from linearity is most marked when the separate rate constants are equal, at the isokinetic temperature T^*. If î…€ is the apparent activation energy and ΔE is the difference in activation energies, then at T^*: î…€=(E₁+E₂)/2, and (dî…€/dT)=R(ΔE/2RT^*)².