Correlations between rate parameters and calculated molecular properties in the reactions of the nitrate radical with alkenes

Abstract

A study of the reactivity of the No₃ radical towards a series of alkenes and halogenoalkenes has been carried out. For those compounds not containing a vinylic chlorine atom, the activation energy, the logarithm of the pre-exponential A factor and the logarithm of the room-temperature rate coefficient (k) correlate strongly with the calculated ionization potential (E_i) of the organic reactant. In the case of alkenes containing vinylic chlorine atoms, the correlations of k and activation barriers with E_i break down, although the correlation between log A and E_i still holds. On the basis of the extent of interaction between the chlorine atom lone-pair orbitals and the carbon–carbon π bond, corrections to the E_i s can be made and the activation barriers and log ks then correlate well with these corrected E_i s. Using these correlations, Arrhenius parameters can be estimated and used to calculate ks, which are compared with measured values. Excellent agreement is observed, providing support for this method of estimating Arrhenius parameters. The observations are rationalized in terms of frontier orbital theory.