Second order rate constants for intramolecular conversions: Application to gas-phase NMR relaxation times

Publisher Website
Google Scholar
Abstract
The usually quoted expression for the second order rate constant, for a unimolecular reaction at the low pressure limit, is valid only for strictly irreversible processes. Its application to isomerizationreactions (which are to some extent reversible) is demonstrably in error; corrected expressions have been published. Attention is directed to intramolecular conversions over low barriers, for which the inappropriateness of the unidirectional expression becomes obvious. For such isomerizations we propose a model which incorporates only operationally observable states, so that an essential conceptual ambiguity is avoided. Use of this model is illustrated for the syn⇄anti conversions of methyl nitrite, derived from a gas phase NMR coalescence curve (M c :T c ). The present data suggest that during isomerization the alkyl nitrites may not be completely ergodic on a time scale of 10−9 s. A regional phase‐space model is proposed which has the appropriate formalism to account for this behavior.